[Enhancement] Brushes

[jsuarezruiz]

Description of Change

Added Brushes support. A Brush "paints" an area with its output. Different brushes have different types of output. Some brushes paint an area with a solid color and others with a gradient.

Examples:

Using the new Background property you can set the background of any Page, Layout or View using a Brush.

<Grid>
    <Grid.Background>
        <LinearGradientBrush StartPoint="0.5,0" EndPoint="0.5,1">
            <GradientStop Color="Yellow" Offset="0.0" />
            <GradientStop Color="Red" Offset="0.25" />
            <GradientStop Color="Blue" Offset="0.75" />
            <GradientStop Color="LimeGreen" Offset="1.0" />
        </LinearGradientBrush>
    </Grid.Background>
<Grid>

Issues Resolved

• fixes (partially) Xamarin.Forms Drawing Spec #2452
• fixes [Enhancement] Add brush support for background #1856
• fixes [Spec] Brushes #7293

API Changes

Added:

public abstract class Brush : BindableObject
{

}

GradientBrush

public class GradientBrush : Brush
{
    public IList<GradientStop> GradientStops { get; set; }
}

GradientStop

public class GradientStop : BindableObject
{
    public Color Color { get; set; }

    public float Offset { get; set; }
}

SolidColorBrush

public class SolidColorBrush : GradientBrush
{

}

LinearGradientBrush

public class LinearGradientBrush : GradientBrush
{
    public Point StartPoint { get; set; }

    public Point EndPoint { get; set; }
}

RadialGradientBrush

public class RadialGradientBrush : GradientBrush
{
    public Point Center { get; set; }

    public double Radius { get; set; }
}

Platforms Affected

• Core/XAML (all platforms)
• iOS
• Android
• macOS
• UWP
• WPF

Behavioral/Visual Changes

None

Testing Procedure

Launch Core Gallery and navigate to the new Gradients Gallery.

Screenshots

Notes

• BackgroundColor property will be deprecated.

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[jcmanke]

What should happen with the BackgroundColor property?. In the current state of the PR can use BackgroundColor (Color) and Background (Brush) properties at the same time. If both properties are used, BackgroundColor is ignored, but should we deprecate BackgroundColor?

Basically, I don't want to ever create a SolidColorBrush object in either XAML or code, I just want to specify the color. There should be an implicit converter so that Background = Color.Blue works. (If this is already included, great. I haven't looked through the files yet.)

[jsuarezruiz]

@jcmanke This PR is still a Draft and we continue working on it so, thanks for your feedback. A TypeConverter was added to allow Background="Red".

[MichaelStgt]

I had a closer look at the source and the sample inside the Gallery.
I assume that x = 0 and y = 0 is the upper left corner of the Element.

Your example contains two for a LinearGradientBrush, where one is

**HorizontalLinearGradient**
StartPoint="0, 0"
EndPoint="1, 0"

and the other one is

**VerticalLinearGradient**
StartPoint="0, 0"
EndPoint="0, 1"

But should it not be like this:

**FromTopLeftToBottomRight (diagonal)**
StartPoint="0, 0"
EndPoint="1, 1"

**HorizontalLinearGradient**
StartPoint="0.5, 0"
EndPoint="0.5, 1"

**VerticalLinearGradient**
StartPoint="0, 0.5"
EndPoint="1, 0.5"

**FromTopRightToBottomLeft (diagonal)**
StartPoint="1, 0"
EndPoint="0, 1"

[PureWeen]

Looks like this is failing the Automated platform tests

[PureWeen]

As a general comment I would say the updatebrush/updatecolor code in the renderers should be consistently setup so updatecolor isn't called if the user sets the brush

For example in TabbedPageRenderer both updates get called when the control is initialized.

https://github.com/xamarin/Xamarin.Forms/pull/9220/files#diff-7feeca82b01e77527e9263a06421f443R782

I think in general UpdateColor/UpdateBrush code should always just call into UpdateBrush and then if the Brush is set call that code otherwise call UpdateColor

For example on ImageButtonRenderer here they both call the same method
https://github.com/xamarin/Xamarin.Forms/pull/9220/files#diff-8295d11d94d3eaa6d894cb727a46be12R104

We don't have to make this change as part of this PR but I wonder how much of this should be at the xplat layer. Can we make it so all the Color properties just set the Brush?

[samhouts]

Please rebase to fix conflicts, then merge!!!! THANKS! :D

[jsuarezruiz]

@PureWeen Reviewed Shell FlyoutBackground: