Tag Archives: Gradient Effects

Publishing the Nuget of my Color Picker Control for Xamarin.Forms!

Let me share the journey of me publishing the Nuget Package of my interactive Color Picker Control for Xamarin.Forms that I built using SkiaSharp.

So some time back I built an Interactive and responsive Color Picker Control for Xamarin.Forms (Android, iOS, UWP) with a whole bunch of awesome features. On a Canvas with a beautiful Color spectrum similar to a rainbow gradient effect spreading across, drag, drop, swipe and pan over the Canvas to pick the Color you need easily, in a fun-to-use interactive experience. Built from pure Xamarin.Forms based on SkiaSharp, lightweight and fast!

Backstory…

In my previous blog post I shared with you guys how I built my interactive Color Picker Control for Xamarin.Forms, https://theconfuzedsourcecode.wordpress.com/2020/02/26/i-built-an-interactive-color-picker-control-for-xamarin-forms/

Since then I had been adding a whole bunch of extra feature to this Color Picker Control I built, so I thought it was a good idea to publish it as a Nuget Package and share with everyone! 😀

So this time, let me share my journey of implementing more advanced features and publishing the Nuget Package of my Color Picker Control for Xamarin.Forms! 😉

Some thought…

So before I isolated my Color Picker Control into a stand alone reusable package, I wanted to make sure that I maintain my philosophy of building Plugins. This would definitely have a big impact on your Users who will will be using these Plugins to build their apps, therefore I’ll share the tick list that I consider as important as follows…

Plug and Play: The plugin should easy to set up with. Do not force Devs to set up any dependencies or property values by themselves. The properties and behaviors of the Plugin should have default values assigned to them.

Customization: It should be easy and straight forward for the Devs to customize the appearance or the behaviors of the Plugin. In some case this might be limited, but you must build the Plugin in a way it make it easy as much as possible.

Embedded: In the case of UI Element Plugins, you should make it easy to be embedded into any Layout structure, being able to inherit the Parent Layout’s behaviors and values, without overriding or disrupting them.

Keep it Light: Make the Plugin as lightweight as possible, give the Dev the chance to choose which assemblies to be included in the plugin. Remove unnecessary references or dependencies from your Plugin core, so it’s light weight as possible.

Performance First: It shouldn’t cause any performance bottleneck, therefore from scratch you must build the Plugin with performance in mind. Constantly check for performance improvements during the development of your Plugin.

So may be go over this list before you build or release a Plugin for the public! 😉 Alright, with all those principles in mind, let’s move ahead…

The Features!

So here are the features that are already available in the Color Picker Control that I built which I had shared from my previous blog post…

  • Picked Color: The Property that allows Users to retrieve the Color values that’s selected from the Color Picker. This value is only a Get Property.
  • Picked Color Changed Event: The Event that fires up every time the PickedColor Value is changed during Color selection. You can subscribe to this event and observe the behavior.

Since my venture into this Color Picker Plugin I had a few ideas in mind as improvements or rather add as extra features, rather than just being a UI Element which allows you to pick a color on a beautiful spectrum! 😉 So here are the extra features that I’ll be building up into it..

  • Change the Available Base Colors List: You can set the primary list of Colors where the gradient spectrum will be rendered from. So choose the base colors you want to be populated as you wish and it will be rendered on the Color Picker.
  • Change the Color List Flow Direction: You will be able to change the direction of the flow of the colors on the canvas, where it be Horizontal flow or a Vertical flow of the color spectrum. Further more Horizontally being starting off the flow from left to right, and Vertically being top to bottom.
  • Change the Color Spectrum Style: You will be able to change the style of the Color Spectrum gradient, the rendering combination of base colors (Hue), or lighter colors (Tint) or darker colors (Shade). You’ll be able to set it with different order as well, ex: Hue Colors, Shade Colors, Tint Colors or Tint Colors, Hue Colors, Shade Colors, etc..
  • Change the Appearance of the Pointer: The white color circle that is used as the Picker Pointer on the Canvas, should be able to customized based on its Diameter or Thickness of the Circle border. Another nice addition would be to allow user to set the position of the Pointer as they wish.

Alright, now that we listed down the new intended feature set that I’m planning to ship out with my Color Picker Control, let’s get down to building it… 😀

Sneak Peek!

Just to give a little glimpse of the awesomeness I ended up building and publishing… 😀 behold the Color Picker Control for Xamarin.Forms!

Pretty awesome eh! 😉 I have moved out of my previous repo to a new standalone repo in github, since I’m publishing this as a package. Therefore all the new development will be done in this repository.

Project hosted on github:
https://github.com/UdaraAlwis/XFColorPickerControl

So feel free to take a look in there before we continue… 😉

Time to Build!

Since I already explained in my previous blog post how I built my Color Picker Control from scratch step by step, I won’t be repeatedly going through same code bits in this post, but rather focus on the new changes and features only.
If you haven’t read that one yet, then I would recommend you take a peek there first, I built an Interactive Color Picker Control for Xamarin.Forms! And continue here…

I named the Solution as Udara.Plugin.XFColorPickerControl, and in return I intend to keep the Package reference with the same naming. I am using Visual Studio 2019 on Windows 10 here as my development environment.

I have created a VS Solution with a .NET Standard 2.0 Library which will hold the UI Control in place, with the naming ColorPicker. You can see I have added the dependencies of the Plugin, with Xamarin.Forms and SkiaSharp.Views.Forms packages. 😉

Notice the pure Xamarin.Forms DemoApp project inside the Demo folder that I have added to the same solution? That is for testing and showcasing the Plugin’s use, also as a reference point for anyone who wants to learn how to use the Plugin in many different ways, this attached DemoApp could come handy. 😀

The ColorPicker.xaml is the UI Element that users will be using under the namespace Udara.Plugin.XFColorPickerControl.ColorPicker in their XAML or C# code for building the UI. Here’s base skeleton implementation of the ColorPicker.xaml.cs, which all the core implementation will be taking place…

namespace Udara.Plugin.XFColorPickerControl
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class ColorPicker : ContentView
    {
        public ColorPicker()
        {
            InitializeComponent();
        }

        // Implementation goes here
    }
}

Next let’s get into the implementation of Features one by one as I discussed before…

Building the Features!

So I’m going to use the same code for the two features that I already implemented in my previous blog post, Picked Color and Picked Color Changed Event feature that’s represented by PickedColor Property and PickedColorChanged Event Handler.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
	/// <summary>
	/// Occurs when the Picked Color changes
	/// </summary>
	public event EventHandler<Color> PickedColorChanged;

	public static readonly BindableProperty PickedColorProperty
		= BindableProperty.Create(
			nameof(PickedColor),
			typeof(Color),
			typeof(ColorPicker));

	/// <summary>
	/// Get the current Picked Color
	/// </summary>
	public Color PickedColor
	{
		get { return (Color)GetValue(PickedColorProperty); }
		private set { SetValue(PickedColorProperty, value); }
	}
	
	...
}

Now considering the rest of the features that I discussed in the beginning, all those features can be implemented and exposed via Bendable Properties, and handling the Property Changed events internally to react for any changes requested during run time.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...
 
    public static readonly BindableProperty PropertyNameProperty
        = BindableProperty.Create( 
        ... 
        
            validateValue: (bindable, value) =>
            {
                // validate value
                return (..);
            },
            
            propertyChanged: (bindable, value, newValue) =>
            {
                if (newValue != null)
                    // action on value change
                else
                    // handling null values
                    ((ColorPicker)bindable).PropertyNameProperty = default;
            });
        );
 
    public type PropertyName
    { ... }
 
    ...
}

All the Bindable Properties are safeguarded with validations as you see above. I have added an extra layer of protection against unnecessary null values being set up, by defaulting the property value to default of itself. You can check the full implementation of each of these Properties on the github repo itself. github.com/UdaraAlwis/XFColorPickerControl Let’s begin..

Feature: BaseColorList

Bindable Property, BaseColorList: Change the available base Colors on the Color Spectrum, of the Color Picker. This will take a List of strings of Color names or Hex values, which is held in an IEnumerable as show here, also I have set up the fallback default values with the rainbow color spectrum.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...

    public static readonly BindableProperty BaseColorListProperty
        = BindableProperty.Create( ... );

    public IEnumerable BaseColorList
    { ... }

    ...
}

This Property is then consumed during the SkiaSharp rendering cycle as follows, where as we’re using the Xamarin.Forms built in ColorTypeConverter to parse the string color values to actual Color objects and then to SKColor objects, which is then used to render the render the color spectrum on the Color Picker Control. 😀

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
         
        // Draw gradient rainbow Color spectrum
        using (var paint = new SKPaint())
        {
            paint.IsAntialias = true;
 
            // Initiate the base Color list
            ColorTypeConverter converter = new ColorTypeConverter();
            System.Collections.Generic.List<SKColor> colors = 
                new System.Collections.Generic.List<SKColor>();
            foreach (var color in BaseColorList)
                colors.Add(((Color)converter.
		          ConvertFromInvariantString(color.ToString())).ToSKColor());
				
            ...
        }
    }
...

Pretty straight forward eh! Let’s see how you could use this as a developer.

How to use?

You can easily use this feature in XAML as follows, by accessing ColorPicker.BaseColorList property and setting up the list of color values you prefer as hex values or with pre-defined color value names.

<xfColorPickerControl:ColorPicker
	x:Name="ColorPicker"
	...	>
	<xfColorPickerControl:ColorPicker.BaseColorList>
		<x:Array Type="{x:Type x:String}">
			<!--  Yellow  -->
			<x:String>#ffff00</x:String>
			<!--  Aqua  -->
			<x:String>#00ffff</x:String>
			<!--  Fuchsia  -->
			<x:String>#ff00ff</x:String>
			<!--  Yellow  -->
			<x:String>#ffff00</x:String>
		</x:Array>
	</xfColorPickerControl:ColorPicker.BaseColorList>
</xfColorPickerControl:ColorPicker>

If you prefer in C# code, you can easily do as as well, a list of string values of the colors…

ColorPicker.BaseColorList = new List<string>()
{
	"#00bfff",
	"#0040ff",
	"#8000ff",
	"#ff00ff",
	"#ff0000",
};

Here’s some action…

Feature: ColorFlowDirection

The Bindable Property, ColorFlowDirection: Change the direction in which the Colors are flowing through on the Color Spectrum, of the Color Picker. This will allow you to set whether the Colors are flowing through from left to right, Horizontally or top to bottom, Vertically. I have defined an Enum type which will represent this type of course.

namespace Udara.Plugin.XFColorPickerControl
{
    public enum ColorFlowDirection
    {
        Horizontal,
        Vertical
    }
}

Let’s create our ColorFlowDirection Bindable Property based on that,

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...

    public static readonly BindableProperty ColorFlowDirectionProperty
        = BindableProperty.Create( ... );

    public ColorFlowDirection ColorFlowDirection
    { ... }

    ...
}

The default value will be set as ColorFlowDirection.Horizontal, and if the User changes value during run time, it will fire up a new SkiaSharp rendering cycle of the Canvas, effectively rendering the spectrum accordingly to the new color value, which is handled in the rendering logic as below…

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
        
            // create the gradient shader between base Colors
            using (var shader = SKShader.CreateLinearGradient(
                new SKPoint(0, 0),
                ColorFlowDirection == ColorFlowDirection.Horizontal ?
                    new SKPoint(skCanvasWidth, 0) : 
                    new SKPoint(0, skCanvasHeight),
                colors.ToArray(),
                null,
                SKShaderTileMode.Clamp))
            {
                paint.Shader = shader;
                skCanvas.DrawPaint(paint);
            }
            
        ...
    }
...

The trick here is to configure the SKShader.CreateLinearGradient() method’s start and end coordinate parameters, which governs the direction in which the gradient effect will be drawn with the list of colors, thus rendering the color list from left to right or top to bottom. As you can see for Horizontal effect, we use SKPoint (0,0) to SKPoint(<canvasWidth>, 0) by using the corner most value on the X axis for the end coordinates, the same pattern is used for Vertical effect with bottom most value on the Y axis.

Here how to consume this feature as a developer…

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.ColorFlowDirection property and setting Horizontal or Vertical option as you prefer…

<xfColorPickerControl:ColorPicker
	x:Name="ColorPicker"
	ColorFlowDirection="Horizontal"
	...	>
</xfColorPickerControl:ColorPicker>

If you prefer in C# code, use the ColorFlowDirection.Horizontal or Vertical option…

ColorPicker.ColorFlowDirection =
	Udara.Plugin.XFColorPickerControl.ColorFlowDirection.Horizontal;

Here’s some action…

Feature: ColorSpectrumStyle

The Bindable Property, ColorSpectrumStyle: Change the Color Spectrum gradient style, with the rendering combination of base colors (Hue), or lighter colors (Tint) or darker colors (Shade). If you’re not familiar with these technical terms, here’s a clear illustration of comparison of Hue, Shade, and Tint of Colors.

We need to make sure our Color Picker is able to deliver to this kind of requirement, having darker or lighter colors of the given base colors on the Color Picker Spectrum. So I’ve created an Enum type which will consist of all the possible combinations of Hue, Shade and Tint colors based on the available Base Colors, that would facilitate this feature.

namespace Udara.Plugin.XFColorPickerControl
{
    public enum ColorSpectrumStyle
    {
        HueOnlyStyle,
        HueToShadeStyle,
        ShadeToHueStyle,
        HueToTintStyle,
        TintToHueStyle,
        TintToHueToShadeStyle,
        ShadeToHueToTintStyle
    }
}

Let’s create our ColorSpectrumStyle Bindable Property based on that,

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...

    public static readonly BindableProperty ColorSpectrumStyleProperty
        = BindableProperty.Create( ... );

    public ColorSpectrumStyle ColorSpectrumStyle
    { ... }

    ...
}

I will be setting ColorSpectrumStyle.HueToShadeStyle as the default value for this property, any changes to this value during run time will kick start a new refresh draw on the Color Spectrum, which is handled in the rendering logic as below…

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
         
        // Draw secondary gradient color spectrum
        using (var paint = new SKPaint())
        {
            paint.IsAntialias = true;
 
            // Initiate gradient color spectrum style layer
            var colors = GetSecondaryLayerColors(ColorSpectrumStyle);
			
            ...
        }
    }
...

Over here, we’re retrieving the list of colors based on the ColorSpectrumStyle value, which is a combination of Transparent, Black and White colors, which will be used to draw the secondary gradient layer. GetSecondaryLayerColors() will be returning the appropriate list of secondary colors that matches the ColorSpectrumStyle requested as follows.

...
    private SKColor[] GetSecondaryLayerColors(ColorSpectrumStyle colorSpectrumStyle)
    {
        ...
        
        if (colorSpectrumStyle == GradientColorStyle.DarkToColorsToLightStyle)
        {
            return new SKColor[]
            {
                SKColors.Black,
                SKColors.Transparent,
                SKColors.White
            };
        }
        
        ...
    }
...

I’m maintaining a simple If-else block chain which will check for the ColorSpectrumStyle value available and return the appropriate list of colors back. Quite straight forward! 😉

Now here’s how you use this awesome feature…

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.ColorSpectrumStyle property and setting the appropriate Style option as you prefer…

<xfColorPickerControl:ColorPicker
	x:Name="ColorPicker"
	ColorSpectrumStyle="TintToHueToShadeStyle"
	...	>
</xfColorPickerControl:ColorPicker>

If you prefer in C# code…

ColorPicker.ColorSpectrumStyle =
	Udara.Plugin.XFColorPickerControl.ColorSpectrumStyle.TintToHueToShadeStyle;

Here’s some action…

Feature: PointerRing Styling

As you can see there’s a pretty neat Pointer Ring that’s pointing the picked color position on the Color Picker, it would be nice to be able to customized this too eh! 😉

Therefore I have introduced four features for this,

  • PointerRingDiameterUnits
  • PointerRingBorderUnits
  • PointerRingPositionXUnits
  • PointerRingPositionYUnits

Alright, let’s walk through them one by one..

Feature: PointerRingDiameterUnits

The Bindable Property, PointerRingDiameter: Changes the Diameter size of the Pointer Ring on the Color Picker. It accepts values between 0 and 1, as a representation of numerical units which is compared to the 1/10th of the longest length of the Color Picker Canvas. By default this value is set to 0.6 units.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...
 
    public static readonly BindableProperty PointerRingDiameterUnitsProperty
        = BindableProperty.Create( ... );
 
    public double PointerRingDiameterUnits
    { ... }
    
    ...
}

This will be calculated against the longest length of Color Picker’s Canvas, whether it be Width or Height. The reason for adding another 1/10th of the value is to maintain the maximum size of the Pointer Ring, avoiding ridiculous sizing of the element. lol So the Precise calculation is as, Canvas Size (Height or Width) x PointerRingDiameterUnits x (1/10)
This value will render exactly to the same proportion against different screen sizes and DPs.

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
         
        // Painting the Touch point
        using (var paint = new SKPaint())
        {
            ...
 
            var canvasLongestLength = (skCanvasWidth > skCanvasHeight) 
                    ? skCanvasWidth : skCanvasHeight;

            // Calculate 1/10th of the units value for scaling
            var pointerRingDiameterUnitsScaled = (float)PointerRingDiameterUnits / 10f;
            // Calculate against Longest Length of Canvas 
            var pointerRingDiameter = (float)canvasLongestLength 
                                                    * pointerRingDiameterUnitsScaled;

            // Outer circle of the Pointer (Ring)
            skCanvas.DrawCircle(
                _lastTouchPoint.X,
                _lastTouchPoint.Y,
                (pointerRingDiameter / 2), paintTouchPoint);

            ...
        }
    }
...

I’ve set up the skCanvas.DrawCircle() with the (pointerRingDiameter / 2) since it accepts radius value only for drawing the circle.

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.PointerRingDiameterUnits property and setting the value against your Color Picker’s Width and Height.

<xfColorPickerControl:ColorPicker
    x:Name="ColorPicker"
    PointerRingDiameterUnits="0.6"
    ...    >
</xfColorPickerControl:ColorPicker>

If you prefer in C# code…

ColorPicker.PointerRingDiameterUnits = 0.6;

Here’s some action…

Feature: PointerRingBorderUnits

The Bindable Property, PointerRingBorderUnits: Changes the Border Thickness size of the Pointer Ring on the Color Picker. It accepts values between 0 and 1, as a representation of numerical units which is calculated against the diameter of the Pointer Ring. By default this value is set to 0.3 units.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...
 
    public static readonly BindableProperty PointerRingBorderUnitsProperty
        = BindableProperty.Create( ... );
 
    public double PointerRingBorderUnits
    { ... }
    
    ...
}

This calculation executes against the Pointer Ring’s pixel diameter value as, (Pointer Ring Diameter in Pixels) x PointerRingBorderUnits, since this is dependent on the Pointer Ring’s diameter, we thickens the border inside that circle only. Basic technique here is to draw a Circle inside the Parent Circle, with the picked pixel point’s color, emulating the visual of a Ring.

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
         
        // Painting the Touch point
        using (var paint = new SKPaint())
        {
            ...
 
            // Draw inner circle with picked color
            paintTouchPoint.Color = touchPointColor;

            // Calculate against Pointer Circle
            var pointerRingInnerCircleDiameter 
                          = (float)pointerRingDiameter 
                              * (float)PointerRingBorderUnits; 

            // Inner circle of the Pointer (Ring)
            skCanvas.DrawCircle(
                _lastTouchPoint.X,
                _lastTouchPoint.Y,
                ((pointerRingDiameter 
                        - pointerRingInnerCircleDiameter) / 2), paintTouchPoint);
            ...
        }
    }
...

I’ve set up the skCanvas.DrawCircle() with the calculation, ((pointerRingDiameter – pointerRingInnerCircleDiameter) / 2) since it accepts radius value only for drawing the circle.

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.PointerRingBorderUnits property and setting the value against PointerRingDiameterUnits you have used.

<xfColorPickerControl:ColorPicker
    x:Name="ColorPicker"
    PointerRingBorderUnits="0.3"
    ...    >
</xfColorPickerControl:ColorPicker>

If you prefer in C# code…

ColorPicker.PointerRingBorderUnits = 0.3;

Here’s some action…

Feature: PointerRingPosition<X,Y>Units

The Bindable Property, PointerRingPosition<X,Y>Units: Changes the Pointer Ring’s position on the Color Picker Canvas programmatically. There are of two bindable properties PointerRingPositionXUnits and PointerRingPositionYUnits, which represents X and Y coordinates on the Color Picker Canvas. It accepts values between 0 and 1, as a presentation of numerical units which is calculated against the Color Picker Canvas’s actual pixel Width and Height. By default both the values are set to 0.5 units, which positions the Pointer Ring in the center of the Color Picker.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...
 
    public static readonly BindableProperty PointerRingPositionXUnitsProperty
        = BindableProperty.Create( ... );
 
    public double PointerRingPositionXUnits
    { ... }
	
    public static readonly BindableProperty PointerRingPositionYUnitsProperty
        = BindableProperty.Create( ... );
 
    public double PointerRingPositionYUnits
    { ... }
 
    ...
}

This calculation executes against the Color Picker Canvas’s actual pixel Width and Height as, (Color Picker Canvas Width in Pixels) x PointerRingPositionXUnits and (Color Picker Canvas Height in Pixels) x PointerRingPositionYUnits
Up on invoke of the PropertyChanged on those Properties, we make a call to the following SetPointerRingPosition() with the new X and Y position units requested from User.

...
    private void SetPointerRingPosition
                      (double xPositionUnits, double yPositionUnits)
    {
        // Calculate actual X Position
        var xPosition = SkCanvasView.CanvasSize.Width
                                 * xPositionUnits; 
        // Calculate actual Y Position
        var yPosition = SkCanvasView.CanvasSize.Height
                                 * yPositionUnits; 

        // Update as last touch Position on Canvas
        _lastTouchPoint = new SKPoint(Convert.ToSingle(xPosition), Convert.ToSingle(yPosition));
        SkCanvasView.InvalidateSurface();
    }
...

We’re calculating the actual X and Y coordinates against the Canvas pixel size and setting up the _lastTouchPoint with those values, for keeping the Pointer Ring position on canvas in sync with touch inputs positioning and programmatical positioning, then at the end we fire up the SkiaSharp rendering cycle with SkCanvasView.InvalidateSurface();

Handling Pointer Ring Position on Initialization!

We need to handle the positioning of the Pointer Ring on the initialisation or on the rendering of the element during run time. We can achieve this by a one-time execution with a boolean flag, that executes this logic. So upon the first SkiaSharp canvas rendering cycle, we hook up to the PointerRingPositionXUnits and PointerRingPositionYUnits properties and render the Pointer Ring Position to the set value.

...    
    private bool _checkPointerInitPositionDone = false;

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
          
        if (!_checkPointerInitPositionDone)
        {
            var x = ((float)skCanvasWidth * (float)PointerRingPositionXUnits);
            var y = ((float)skCanvasHeight * (float)PointerRingPositionYUnits);

            _lastTouchPoint = new SKPoint(x, y);

            _checkPointerInitPositionDone = true;
        }
    }
...

We use _lastTouchPoint variable which is used by the drawing functions for rendering the Pointer Ring on Color Picker’s Canvas.

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.PointerRingPositionXUnits property and ColorPicker.PointerRingPositionYUnits setting the values against your Color Picker’s Width and Height.

<xfColorPickerControl:ColorPicker
    x:Name="ColorPicker"
    PointerRingPositionXUnits="0.3"
    PointerRingPositionYUnits="0.7"
    ...    >
</xfColorPickerControl:ColorPicker>

If you prefer in C# code…

ColorPicker.PointerRingPositionXUnits = 0.3;
ColorPicker.PointerRingPositionYUnits = 0.7;

Here’s some action…

UWP Bug Fix!

One issue I noticed was on UWP run time, where the SkiaSharp’s Canvas touch event behaves differently than iOS and Android. The touch event would get activated even if you hover over the canvas using your mouse pointer, and this was causing the PickedColor property to fire up.
The Touch event should occur only if you actually click on the canvas and drag and drop on the Canvas, so in order to fix this I used the InContact property SKTouchEventArgs inside the touch event to validate on UWP run time.

...
    private void SkCanvasView_OnTouch
                (object sender, SKTouchEventArgs e)
    {
        // to fix the UWP touch behavior
        if (Device.RuntimePlatform == Device.UWP)
        {
            // avoid mouse over touch events
            if (!e.InContact)
                return;
        }

        _lastTouchPoint = e.Location;
        
        ...
    }
...

This fixed the bug on UWP, making sure the touch event is validated before executing the rest of the logic.

Nugetizing!

Alright then, its time to set up our beautiful Color Picker Control for Xamarin.Forms as a Nuget Package using Visual Studio. I’m going first set the Nuget package properties first, then build the package, and finally publish it to Nuget, allowing it to be shared with everyone out there! 😀

Set up package properties…

You could do this straight from Visual Studio Project Properties, or directly from a Nuspec file added to the project itself. For now I would prefer setting up properties in VS Project -> Properties – Package tab, making sure to add all the necessary properties and information about the package as shown below…

Make sure to click on “Generate Nuget package on build” tick, which will enable all the property fields. You could also do this by editing .csproj file of the package project as well, if you require any fine tuned editing…

Now we’re ready to build the package of our Udara.Plugin.XFColorPicker library.

Building the Package…

We need to create the Publish Profile for the package.
Right click on Library project node -> Publish

If this was your first time, it will navigate you to create new Publish Profile tab as shown below…

It is easier to set up a Publish Profile, since you don’t have to manually change your build configuration to Release and then launch a build. Therefore I have set it up now, and next time I publish it will straightaway handle all the configuration for you! 😀

Click Publish, and it nicely builds…

Once we navigate to the folder location mentioned in the above build output…

There we have our nupkg package file, which we can then use to directly upload to Nuget!

Upload to Nuget…

Grab that nupkg file and drag and drop into the upload page of nuget.org and you’re done!

Here you’ll be able to add a short marked down documentation for the users, I would highly recommend you do that since it will increase the support and visibility.

Well that’s all it takes, and the package will be available in a few hours on Nuget!

Updating Package…

Now how do we update our package? if you have noticed around nuget, there’s no update option in in the page where you manage the package. You can update your package by using the NuGet command-line utility or directly uploading an increment build, in which I have opted for the end option to keep it easy.

So when you want to push an update to your package, make sure to update the package properties in Visual Studio to reflect the next immediate version, as shown below where I’m updating from version 1.0.2 to version 1.0.3…

Also do no forget the assembly versioning as well…

Now build your package and directly go to nuget upload page, drag and drop the file…

Make sure to add the nuget documentation and Submit!

Done and dusted, just like that, the updating is done! 😀

Published on nuget:
nuget.org/Udara.Plugin.XFColorPickerControl/

Now anyone can use my Color Picker Control for Xamarin.Forms by setting up this nuget package in their project…

Demoing it up!

As you saw at the beginning I have attached a Demo project into the same parent Solution of Udara.Plugin.XFColorPickerControl, which I have used for testing during development, and to maintain as a demonstration of all the awesome features this plugin provides! 😉

Since this plugin is meant to be compatible on a cross platform environment its impeccable do continuous testing on all the platforms. Anyhow here’s a sneak peek of the demo app…

I have created separate pages to demonstrate awesomeness of each special feature…

BaseColorList Demo:

Android, UWP and iOS…

ColorFlowDirection Demo:

Android, UWP and iOS…

ColorSpectrumStyle Demo:

Android, UWP and iOS…

PointerRingStyling Demo:

Android, UWP and iOS…

Since it’s a pure Xamarin.Forms and can be deployed directly to all three platforms, Android, iOS and Windows UWP, you can do the same with my plugin. Feel free to take a look at the demo app in case if you need trouble shooting.

Conclusion!

There you have it my Color Picker Control for Xamarin.Forms, now published to nuget as a package, with a whole bunch of awesome features, and anyone can easily use it in their own Xamarin.Forms projects! 😀 Pheww… What a joy! Sharing something you’ve been working so hard for a long time. So feel free to give a try, contribute, and any feedback is always welcome…

hosted on github:
github.com/UdaraAlwis/XFColorPickerControl

published on nuget:
nuget.org/Udara.Plugin.XFColorPickerControl/

Well that was fun! So keep in mind I’m going to be implementing more and more features for this plugin in future, and might end up changing some of those features or implementations as well. This blog post will not be constantly updated against them, so many sure to keep in touch with the docs in the github repo itself for future references.

Imagination is the limit yol! 😉

Share the love! 😀 Cheers!

I built an Interactive Color Picker Control for Xamarin.Forms!

Let me share my adventure of building an awesome interactive and responsive Color Picker UI Control for Xamarin.Forms with the help of a little SkiaSharp magic! 😉

To blow your mind, imagine something similar to the Color Picker your have in Ms Paint, HTML Web Color Picker or Google Search Web Color Picker…

Think of how interactive and fun to use those UI Elements are, with their drag and drop pointers on the color spectrum which picks up the color from wherever you drop it.

Why can’t we have the same easy to use fun interactive experience in our Xamarin.Forms apps?

Color Picker control is something that’s missing out of the box in Xamarin.Forms, even when it comes to 3rd party controls out there, neither of them are interactive or responsive, let along any fun to use all. lol 😀

Backstory…

Some time back, I ventured in a project where it required me to build a Color Picking UI element, where it would be easy to use for the user to have a similar experience to what we have with Ms Paint, or Web Color Picker UI elements. So I started off by looking at existing 3rd party library controls out there, which ended up me being disappointed seeing all the controls are just static boring color selection lists of grid style elements.

So I started building my own interactive fun-to-use Color Picker from scratch modeled after the Color Picker UI controls we have in Ms Paint, HTML Web Color Picker, etc… The awesomeness of this would allow you to touch, swipe and pan across a beautiful spectrum of color scheme and pick the color you desire! 😀

So… What?

So what we really need to build in this case is, create a Canvas with a full Color spectrum similar to a rainbow gradient effect spreading across, while allowing the User to touch at any given pixel point, up on which an event will trigger capturing the Color value of that pixel point. Also we should be able to highlight that touch triggered pixel point, giving the feedback to the User.

How? in a Gist…

Frankly this is not possible at all, out of the box in Xamarin.Forms, but with the help of a little SkiaSharp magic, this would be possible! SkiaSharp is the awesome 2D graphics rendering library that let’s you do all kinds of cool stuff on top of Xamarin.Forms. So basically we’re going to draw the full Color spectrum with a rainbow-gradient style spreading across a 2D canvas with the help of SkiaSharp.

We will define the list of main colors we need to include across the Canvas, while defining the Gradient fading effect between them. Then with regards to Touch, we need to enable this on the SkiaSharp canvas, and subscribe to the touch handling events.

Then given the User triggers a touch even on the Canvas, we will pick up those coordinate values on the canvas, and pick the Color values of the Pixel at that point on the Canvas. Voiala! We got the Color value picked by the User! 😉 Then as a responsive feedback we will draw highlighting circle around that pixel point coordinates on the Canvas. 😀

Well there you have it, quite straight forward eh! 😉

Sneak Peak!

Just to give a little sneak peak, here’s what I build… 😀 Behold the Interactive Color Picker Control for Xamarin.Forms!

Pretty awesome eh! Xamarin.Forms + SkiaSharp magic! 😉

Project hosted on github:  
https://github.com/UdaraAlwis/XFColorPickerControl 

Alright then let me show you how I built it…

Let’s start building!

Let’s begin by adding SkiaSharp to our Xamarin.Forms project. Open up Nuget Package Manager on your Xamarin.Forms solution node and add SkiaSharp.View.Forms Nuget to your .NET Standard project node and platform nodes as shown below…

That’s it, no extra set up is needed… 😉

Next we need to create our Custom Control, which I’m going to name as ColorPickerControl!

The ColorPickerControl!

It’s better to keep this in a dedicated folder in the .NET Standard project, inside a “Controls” folder, for the sake of clarity! 😉 So let’s create our ColorPickerControl as a type ContentView XAML element in the Controls folder…

<?xml version="1.0" encoding="utf-8" ?>
<ContentView
    x:Class="XFColorPickerControl.Controls.ColorPickerControl"
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:d="http://xamarin.com/schemas/2014/forms/design"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <!-- Content of the Control -->

</ContentView>

Then as of the code behind, let’s set up a PickedColor Property that holds the value of the Color that User picks during the run time, and an event that fires itself up on that action, PickedColorChanged event!

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPickerControl : ContentView
{
	public event EventHandler<Color> PickedColorChanged;

	public static readonly BindableProperty PickedColorProperty
		= BindableProperty.Create(
			nameof(PickedColor),
			typeof(Color),
			typeof(ColorPickerControl));

	public Color PickedColor
	{
		get { return (Color)GetValue(PickedColorProperty); }
		set { SetValue(PickedColorProperty, value); }
	}

	public ColorPickerControl()
	{
		InitializeComponent();
	}
}

Alright next on to setting up the SkiaSharp bits in our Control…

The SkiaSharp magic!

SkiaSharp’s magical Canvas called SKCanvasView is what we’re going to use to Draw our Rainbow Color Spectrum and handle all the Touch event bits… So let’s begin by adding the SKCanvasView to our ColorPickerControl XAML and also the SkiaSharp.Views.Forms reference in the XAML itself..

<ContentView
    ...
    xmlns:skia="clr-namespace:SkiaSharp.Views.Forms;assembly=SkiaSharp.Views.Forms"
	...
	>

    <skia:SKCanvasView
        x:Name="SkCanvasView"
        EnableTouchEvents="True"
        PaintSurface="SkCanvasView_OnPaintSurface"
        Touch="SkCanvasView_OnTouch" />

</ContentView>

Code on Github: /XFColorPickerControl/Controls/ColorPickerControl.xaml

As you can see on my SKCanvasView element, I have enabled touch events with EnableTouchEvents property and subscribed to Touch event with SkCanvasView_OnTouch. Subscribing to PaintSurface allows us to draw full blown 2D graphics on the Canvas, which is why we have created the event SkCanvasView_OnPaintSurface event.

So let’s handle all those events in the code behind of our ColorPickerControl…

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPickerControl : ContentView
{
	...
	
	private void SkCanvasView_OnPaintSurface
                      (object sender, SKPaintSurfaceEventArgs e)
	{
		var skImageInfo = e.Info;
		var skSurface = e.Surface;
		var skCanvas = skSurface.Canvas;

		var skCanvasWidth = skImageInfo.Width;
		var skCanvasHeight = skImageInfo.Height;

		skCanvas.Clear(SKColors.White);

		...
	}
	
	private void SkCanvasView_OnTouch
                      (object sender, SKTouchEventArgs e)
	{
		...
	}
}

Code on Github: /XFColorPickerControl/Controls/ColorPickerControl.xaml.cs

So we’re setting up the basic values we need to use inside SkCanvasView_OnPaintSurface with the skImageInfo, skSurface, skCanvas, which will be very useful in our next set of code snippets!

This is where our core implementation is going to be taking place, let me get into details of each code snippet one by one, but you can always go back to the full code on github and take a look by yourself… 😉 Let’s continue…

The Touch!

Let me begin diving in with the SkCanvasView_OnTouch event method implementation, which handles the touch events occurs on the SkiaSharp Canvas we added into our Control.

We need to keep a track on each Touch event that occurs, so we will store that in a local variable _lastTouchPoint which is of type SKPoint. Since we need to only consider the touch events that occur inside the canvas region, we’re validating each touch coordinate (X,Y) that comes into the event.

...
	private void SkCanvasView_OnTouch
	               (object sender, SKTouchEventArgs e)
	{
		_lastTouchPoint = e.Location;

		var canvasSize = SkCanvasView.CanvasSize;

		// Check for each touch point XY position to be inside Canvas
		// Ignore any Touch event ocurred outside the Canvas region 
		if ((e.Location.X > 0 && e.Location.X < canvasSize.Width) &&
			(e.Location.Y > 0 && e.Location.Y < canvasSize.Height))
		{
			e.Handled = true;

			// update the Canvas as you wish
			SkCanvasView.InvalidateSurface();
		}
	}
...

Based on the validated touch event coordinate, we’re firing up the SkiaSharp Canvas drawing cycle, SkCanvasView.InvalidateSurface(), where we will handle, picking up the color on the touch point and redrawing the canvas to highlight the touch point coordinates on the Canvas.

The Rainbow Color Spectrum!

So this right here is the most critical functionality that we need to implement, drawing the beautiful rainbow gradient color spectrum on our SkiaSharp Canvas. We’re going to draw the following list of colors across the spectrum, which values I picked up with the help of Google Web Color Picker..

Red | Yellow | Green (Lime) | Aqua | Blue | Fuchsia | Red
undefined

This will take place in our SkCanvasView_OnPaintSurface event method that we created in the previous step, where we create the Paint object that’s going to draw the color spectrum on the Canvas, along with the gradient fading effect between all the colors using SKShader object.

...
	private void SkCanvasView_OnPaintSurface
	               (object sender, SKPaintSurfaceEventArgs  e)
	{
		// Draw gradient rainbow Color spectrum
		using (var paint = new SKPaint())
		{
			paint.IsAntialias = true;

			// Initiate the primary Color list
			// picked up from Google Web Color Picker
			var colors = new SKColor[]
			{
				new SKColor(255, 0, 0), // Red
				new SKColor(255, 255, 0), // Yellow
				new SKColor(0, 255, 0), // Green (Lime)
				new SKColor(0, 255, 255), // Aqua
				new SKColor(0, 0, 255), // Blue
				new SKColor(255, 0, 255), // Fuchsia
				new SKColor(255, 0, 0), // Red
			};

			// create the gradient shader between Colors
			using (var shader = SKShader.CreateLinearGradient(
				new SKPoint(0, 0),
				new SKPoint(skCanvasWidth, 0),
				colors,
				null,
				SKShaderTileMode.Clamp))
			{
				paint.Shader = shader;
				skCanvas.DrawPaint(paint);
			}
		}
	}
...

As you can see we are defining the list of Colors with SKColor objects, that’ll populate the rainbow color spectrum on our Canvas. Then we use SKShader.CreateLinearGradient() method to build the gradient shader using the list of colors, and then we draw it on the Canvas using skCanvas.DrawPaint().

Keep a note how SKPoint() objects define the starting and ending coordinates on the Canvas which the shader will spread through, thus we’re taking skCanvasWidth picking the corner most value on the X axis. 😉

The Darker Gradient Strip!

Next we need to draw the darker shadow gradient strip on the Canvas allowing Users to pick the Darker Colors of the primary colors we defined.

We’re going to paint the darker color regions by drawing another layer on top of the previous drawn layer creating the illusion of darker regions of each color.

This will take place in our SkCanvasView_OnPaintSurface but below the code snippet that I showed before. Very much similar to the previous snippet, we’re doing almost the same thing but adding a darker gradient region at the bottom of the Canvas.

...
	private void SkCanvasView_OnPaintSurface
	               (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Draw darker gradient spectrum
		using (var paint = new SKPaint())
		{
			paint.IsAntialias = true;

			// Initiate the darkened primary color list
			var colors = new SKColor[]
			{
				SKColors.Transparent,
				SKColors.Black
			};

			// create the gradient shader 
			using (var shader = SKShader.CreateLinearGradient(
				new SKPoint(0, 0),
				new SKPoint(0, skCanvasHeight),
				colors,
				null,
				SKShaderTileMode.Clamp))
			{
				paint.Shader = shader;
				skCanvas.DrawPaint(paint);
			}
		}
	}
...

Here we’re drawing the darkening gradient layer starting from Transparent color to Black color across the Y axis, thus we’re taking skCanvasHeight picking the corner most value on the Y axis similar to what we did before. 😉

Here they are side by side, before and after drawing darker gradient strip… 😀

The Lighter Gradient Strip!?

This this is bit of an extra cherry on top, as you may have seen some of those Color Pickers include picking Lighter versions of the Colors. We can easily do this by adding a White color object to the list of colors in the code snippet I shared above.

...         
	...
		 ...
			// Initiate the darkened primary color list
			var colors = new SKColor[]
			{
				SKColors.White,
				SKColors.Transparent,
				SKColors.Black
			};  
		 ...
	...
...	

This will draw the secondary layer with White | Transparent | Black gradient effects on top of the full color spectrum layer.

There you go, with the Lighter color gradient strip. Although I wouldn’t include this in my demo app code 😛 Just coz I don’t like it! lol

Picking the Color on Touch!

This is the most crucial bit of this Control, also the most time consuming implementation I had to go through during my trial and error experimentation to get this working! 😮

We are going to be using the _lastTouchPoint SKPoint object, that we created before, in order to access the coordinate data of the touch point on Canvas. Then we look for extract the pixel color values on that coordinate on the Canvas, given that the Canvas is already rendered with the Color spectrum.

This will take place in our SkCanvasView_OnPaintSurface event method, below the color spectrum drawing code snippet.

Experimentation Phase…

Picking a pixel on the rendered Canvas layer is not a straight forward task, the idea here is to capture a quick snapshot of the Canvas graphic layer and convert that into a bitmap image, and use that image to pick the pixels from using the touch coordinates.

As you can see from below, the first implementation I put together which captures a snapshot of the Canvas surface layer and load it into a SKBitmap image, then I retrieve the Pixel data on that image using bitmap.GetPixel() by passing in the touch point values.

...
	private void SkCanvasView_OnPaintSurface
				   (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Picking the Pixel Color values on the Touch Point

		// Represent the color of the current Touch point
		SKColor touchPointColor;

		//// Inefficient: causes memory overload errors
		//using (var skImage = skSurface.Snapshot())
		//{
		//	using (var skData = skImage.Encode(SKEncodedImageFormat.Webp, 100))
		//	{
		//		if (skData != null)
		//		{
		//			using (SKBitmap bitmap = SKBitmap.Decode(skData))
		//			{
		//				touchPointColor = bitmap.GetPixel(
		//									(int)_lastTouchPoint.X, (int)_lastTouchPoint.Y);
		//			}
		//		}
		//	}
		//}
		
		...
	}
...

Later it started causing performance issues due to calling Snapshot() method during each rendering cycle, which is a very heavy process, and even sometimes overloads the memory.

Better Solution…

So after a bit more exploration with trial and error, I managed to build a solution based on a Xamarin Forum response that I found to a similar requirement I had…
https://forums.xamarin.com/discussion/92899/read-a-pixel-info-from-a-canvas

What if instead of taking a snapshot, we use SKImageInfo object of the Canvas instance and extract a SKBitmap image and read the pixel color data of the touch point coordinates. This is way more efficient and consumes much less memory for execution… 😉

...
	private void SkCanvasView_OnPaintSurface
				   (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Picking the Pixel Color values on the Touch Point

		// Represent the color of the current Touch point
		SKColor touchPointColor;

		// Efficient and fast
		// https://forums.xamarin.com/discussion/92899/read-a-pixel-info-from-a-canvas
		// create the 1x1 bitmap (auto allocates the pixel buffer)
		using (SKBitmap bitmap = new SKBitmap(skImageInfo))
		{
			// get the pixel buffer for the bitmap
			IntPtr dstpixels = bitmap.GetPixels();

			// read the surface into the bitmap
			skSurface.ReadPixels(skImageInfo,
				dstpixels,
				skImageInfo.RowBytes,
				(int)_lastTouchPoint.X, (int)_lastTouchPoint.Y);

			// access the color
			touchPointColor = bitmap.GetPixel(0, 0);
		}
		
		...
	}
...

As you can see we’re using skSurface.ReadPixels() to load the pixel data on the coordinates, and finally loading the exact pixel data into touchPointColor as a SKColor object type. 😀

So now we picked the Color from a given touch point on the Canvas, let’s move to the next bit…

The Touch Feedback!

This is the part where we provide on touch feedback for the User by highlighting the touch point on the Canvas up on each touch event. As you noticed we’re firing up the OnPaintSurface event upon each touch event of the Canvas, hence we can draw the highlighting region on the Canvas right here as a feedback loop.

We’re simply going to create a SKPaint object, with White color and use skCanvas.DrawCircle() to draw a circle around the touch point coordinates on the Canvas. Then as an added extra, I’m drawing another circle on top of it with the picked color, so that we can emphasize on the pixel color of the touch point. 😉

...
	private void SkCanvasView_OnPaintSurface
				   (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Painting the Touch point
		using (SKPaint paintTouchPoint = new SKPaint())
		{
			paintTouchPoint.Style = SKPaintStyle.Fill;
			paintTouchPoint.Color = SKColors.White;
			paintTouchPoint.IsAntialias = true;

			// Outer circle (Ring)
			var outerRingRadius = 
				((float)skCanvasWidth/
                    (float)skCanvasHeight) * (float)18;
			skCanvas.DrawCircle(
				_lastTouchPoint.X,
				_lastTouchPoint.Y,
				outerRingRadius, paintTouchPoint);

			// Draw another circle with picked color
			paintTouchPoint.Color = touchPointColor;

			// Outer circle (Ring)
			var innerRingRadius = 
				((float)skCanvasWidth/
                    (float)skCanvasHeight) * (float)12;
			skCanvas.DrawCircle(
				_lastTouchPoint.X,
				_lastTouchPoint.Y,
				innerRingRadius, paintTouchPoint);
		}
		
		...
	}
...

As you can see _lastTouchPoint X and Y coordinates to draw the circle, and we’re calculating the radius value for both circles by adjacent to Canvas width and height, so it renders nicely on any device scale.

And then to the final step, returning back the Color that we Picked from our ColorPickerControl!

Return the Picked Color!

Now we need to return back the Color value that the User picked, to the subscribers or whoever’s listening to the PickedColor property and PickedColorChanged event.

...
	private void SkCanvasView_OnPaintSurface
				   (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Set selected color
		PickedColor = touchPointColor.ToFormsColor();
		PickedColorChanged?.Invoke(this, PickedColor);
		
		...
	}
...

It’s as simple as setting the Value and firing up the Event with the new Color value parameter…

Alright, that’s it! We’ve finished building our awesome ColorPickerControl! 😀

Let’s try it out!

Since we created it as a standalone UI Control you can use this little awesomeness anywhere in your Xamarin.Forms project as you would with any UI element as easy as below…

<controls:ColorPickerControl 
	x:Name="ColorPicker"
	PickedColorChanged="ColorPicker_PickedColorChanged" />

So let’s try adding this to a ContentPage with a nice little Frame element around it with a fixed Height and Width…

<Frame
	x:Name="ColorPickerFrame"
	CornerRadius="8"
	HeightRequest="200"
	HorizontalOptions="Center"
	WidthRequest="350">
	<controls:ColorPickerControl 
		x:Name="ColorPicker"
		PickedColorChanged="ColorPicker_PickedColorChanged" />
</Frame>

This will give a nice little frame around the Color picker control, then on to the code behind…

private void ColorPicker_PickedColorChanged
			(object sender, Color colorPicked)
{
	ColorPickerHolderFrame.BackgroundColor = colorPicked;
}

PickedColorChanged provide you the picked Color value, so you can do what you wish with it!

Fire it up!

Time to fire it up yo! 😀 I’ve prepared a little demo app with my awesome ColorPickerControl for Xamarin.Forms, deployed for Android, iOS and UWP…

Android, iOS and UWP side by side working like a charm! 😀

Project hosted on github:  
https://github.com/UdaraAlwis/XFColorPickerControl 

The possibilities are endless, just a matter of your own creativity! 😉

Conclusion…

An interactive and responsive Color Picker is something that’s missing from Xamarin.Forms out of the box, even when it comes existing to 3rd party controls, there’s no such that fills the requirement, similar to MS Paint Color Picker, or HTML Web Color Pickers.

You can do all kinds of cool interactive 2D graphics rendering stuff with SkiaSharp on Xamarin.Forms, and thanks this, I managed to build a full fledged interactive and fun-to-use Color Picker UI Control, which is lacking in Xamarin.Forms ecosystem right now.

I’m planning to release a nuget package with this control quite soon, with a whole bunch of extra cool features embedded in 😉 So keep in touch!

Imagination is the limit yol! 😉

Share the love! 😀 Cheers!

I’m building an Atom Simulation with SkiaSharp and Xamarin.Forms!

So lately I’ve been on quite a bunch of adventures with SkiaSharp in Xamarin.Forms! 😀 You know how it is for me, pushing the limits of the framework as usual for the fun 😉 And this right here is one of those adventures I’m going to share with you all…

Little Backstory…

I’ve always been fascinated by the Atom’s graphical structure being the science nerd back in school days. I’ve always loved the simulation of the Electrons circulating around the atom’s core filled with Neutrons and Protons. 😀 So while reminiscing those memories, I was thinking of ways to play around with SkiaSharp framework, and suddenly, AHA! A light bulb lit-up on my head! 😀

I’ve decided to build an Atom Simulation in SkiaSharp, with Xamarin.Forms! 😉

A sneak peek!

  

TADAAA! 😀

So where is it going?

Haven’t you ever thought those animated atom structure simulation they show on TV was very very cool? Well I’m thinking of building a similar simulation with SkiaSharp on top of Xamarin.Forms! 😀

And this is going to be a step by step process, where I shall begin with the basic 2D structure and slowly moving towards the complex animated simulation!

Well I’ve already started developing this some time back, and I’ve made quite a bit of progress.

I have hosted this on Github: github.com/UdaraAlwis/SkiaSharpAtomStructureSo that anyone can try it out or add improvements to it, and yes I’m open for pull requests! 😉

Code behind tech bits?

Well basically as you may have already figured out, it’s a Xamarin.Forms project, and I’m using the awesome SkiaSharp for rendering the graphics.

And to be specific with SkiaSharp I’m using the following to render the cool stuff:

  • 2D Shapes Drawing
  • Canvas Translations and Rotations
  • Continuous Animation Rendering
  • Gradient Shading
  • Touch handling

Pretty cool set of features right there, out of the box with SkiaSharp eh! 😉

Progress so far…

I’ve broken the progressive steps to several Pages in the project for clear distinction between the code behind.

I will be updating this post as the project moves forward with improvements and new progression steps.

And here they are…

1. Atom Silhouette

 

So the first step was to simply build a silhouette of the atom structure. There you have the core with Neutrons and Protons, and the Electrons around it in their own orbits.

Basically I’m using the SkCanvas.DrawCircle() to draw the center core and then SkCanvas.DrawOval() to draw the Oval Orbits around the core. 😉

Then I’m drawing the “Electron dot” for each orbit using the corner most point of the Oval Orbit, which is basically the width of the Oval. Tricky yeah!

You might think how about the angles of the oval? Oh yeah I’m using Canvas Rotation for each orbit draw cycle, SkCanvas.RotateDegrees(xx degrees)! 😀

And there’s a simple +/- increment mechanism for increasing and decreasing the number of electrons around the orbit!

You can take a look at the implementation: AtomSilhouettePage.xaml.cs

2. Atom Orbital Paths

 

Here’s a little improvement for the previous step, where as I’ve added some gradient effect for the drawing of the Oval path with the same SkCanvas.DrawOval() call.

The CreateSweepGradient() is one of the way to create a gradient color effect in SkiaSharp, whereas we’ve used white and dark gray as the color here.

Oh Gradients are always cool yeah! 😉

You can take a look at the implementation: AtomOrbitalPathsPage.xaml.cs

3. Atom Orbital Paths Uneven

 

Now we know in reality the Atom’s electron orbit is not a nice even orbit, so we’re going to reflect just that in this progress step! 😀

So basically I’m randomly generating the Oval’s supposed width for each orbit, thus giving the above output!

You can take a look at the implementation: AtomOrbitalPathsUnevenPage.xaml.cs

4. Atom Animated Silhouette

 

This is the step where I kick it up a notch, with the Animation rendering using SkiaSharp!

So as we all know there’s no direct animation rendering support with SkiaSharp, since its a on demand 2D vector graphics rendering system.

What I’m doing here to get the electron dot’s to movement on the oval orbit, is I’m rendering it’s each 360 degrees positions continuously on a timer loop. Might sound pretty complex, but its actually simple! 😉

You can take a look at the implementation: AtomAnimatedPage.xaml.cs

5. A cool touch feature!

I’ve added something cool for the number of displayed Electron’s incremental mechanism!

 

I’ve added a touch handling feature to the atom’s electron incremental mechanism, so now basically you can swipe up or down the screen to increase or decrease the number of electron orbits of the Atom! 😉 Now instead of clicking on the +/- buttons, rather you could swipe up or down to increase or decrease the electron orbits.

This was done simply using the SkiaSharp’s built in touch event handler, and calculating the touch movement direction, thus determining up or down direction! 😀

6. Atom Animated Uneven Orbits

 

So here’s the next progression step, with uneven orbits animation! I’m using a gradient oval drawing for each orbit, similar to what I’ve explained above in one of the previous steps. And I’m generating the Orbits Width upon a given random value.

You can take a look at the implementation: AtomAnimatedUnevnOrbitsPage.xaml.cs

7. ….T B C…..

This will be the next progression step. Since this post will be a continuously updated post along with every progression step I make in this fun project! 😀 So stay tuned!

 

 

That’s all for now!

So like I said at the beginning, this is a continuous fun protect, which I’ll keep on improving step by step. And once again, I will be accepting your pull requests for any improvements you suggest, or just drop a comment or message me of your suggestions. 😀

Don’t forget, feel free to try this project from my Github repo: github.com/UdaraAlwis/SkiaSharpAtomStructure 

I will be updating this post as the project progresses on hopefully! 😉