Pixiview/Gallery.Android/Renderers/RoundLabelRenderer.cs

using Android.Content;
using Android.Graphics;
using Android.Graphics.Drawables;
using Gallery.Droid.Renderers;
using Gallery.UI;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ExportRenderer(typeof(RoundLabel), typeof(RoundLabelRenderer))]
namespace Gallery.Droid.Renderers
{
    public class RoundLabelRenderer : Xamarin.Forms.Platform.Android.FastRenderers.LabelRenderer
    {
        public RoundLabelRenderer(Context context) : base(context)
        {
        }

        protected override void OnElementChanged(ElementChangedEventArgs<Label> e)
        {
            base.OnElementChanged(e);

            if (e.NewElement is RoundLabel label)
            {
                var density = Resources.DisplayMetrics.Density;
                var drawable = new RoundCornerDrawable(label.CornerRadius * density);
                drawable.SetColorFilter(label.BackgroundColor.ToAndroid(), PorterDuff.Mode.Src);
                Control.SetBackground(drawable);
            }
        }
    }

    public class RoundCornerDrawable : Drawable
    {
        private readonly Paint paint;
        private readonly float radius;
        private RectF rect;

        public override int Opacity => (int)Format.Translucent;

        public RoundCornerDrawable(float radius)
        {
            paint = new Paint
            {
                AntiAlias = true
            };
            this.radius = radius;
        }

        public override void SetBounds(int left, int top, int right, int bottom)
        {
            base.SetBounds(left, top, right, bottom);
            rect = new RectF(left, top, right, bottom);
        }

        public override void Draw(Canvas canvas)
        {
            canvas.DrawRoundRect(rect, radius, radius, paint);
        }

        public override void SetAlpha(int alpha)
        {
            paint.Alpha = alpha;
        }

        public override void SetColorFilter(ColorFilter colorFilter)
        {
            paint.SetColorFilter(colorFilter);
        }
    }
}