Black to Transparent Gradient

GradientBack.cs

using System;
using SkiaSharp;
using SkiaSharp.Views.Forms;
using Xamarin.Forms;

namespace XamCAT.Forms.Controls
{
    public class GradientBack : ContentView
    {
        public GradientBack()
        {
            SKCanvasView canvasView = new SKCanvasView();
            canvasView.PaintSurface += OnCanvasViewPaintSurface;
            Content = canvasView;
        }

        void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs args)
        {
            SKImageInfo info = args.Info;
            SKSurface surface = args.Surface;
            SKCanvas canvas = surface.Canvas;
            
            canvas.Clear();

            using (SKPaint paint = new SKPaint())
            {
                // Create 300-pixel square centered rectangle
                float x = 0;
                float y = 0;
                SKRect rect = new SKRect(x, y, info.Width, info.Height);
                
                // Create linear gradient from upper-left to lower-right
                paint.Shader = SKShader.CreateLinearGradient(
                                    new SKPoint(rect.MidX, rect.Top),
                                    new SKPoint(rect.MidX, rect.Bottom),
                                    new SKColor[] { SKColors.Black.WithAlpha(0), SKColors.Black },
                                    new float[] { 0, .8f },
                                    SKShaderTileMode.Clamp);

                // Draw the gradient on the rectangle
                canvas.DrawRect(rect, paint);
            }
        }
    }
}