Shaker/Avalonia/SukiUI/Utilities/Effects/EffectDrawBase.cs

using System;
using System.Diagnostics;
using Avalonia;
using Avalonia.Media;
using Avalonia.Platform;
using Avalonia.Rendering.Composition;
using Avalonia.Rendering.SceneGraph;
using Avalonia.Skia;
using Avalonia.Styling;
using SkiaSharp;
using SukiUI.Models;

namespace SukiUI.Utilities.Effects
{
    public abstract class EffectDrawBase : CompositionCustomVisualHandler
    {
        public static readonly object StartAnimations = new(), StopAnimations = new(), 
            EnableForceSoftwareRendering = new(), DisableForceSoftwareRendering = new();
        
        private SukiEffect? _effect;

        public SukiEffect? Effect
        {
            get => _effect;
            set
            {
                var old = _effect;
                if (Equals(old, value)) return;
                _effect = value;
                EffectChanged(old, _effect);
            }
        }

        private bool _animationEnabled;
        public bool AnimationEnabled
        {
            get => _animationEnabled;
            set
            {
                if (value) _animationTick.Start();
                else _animationTick.Stop();
                _animationEnabled = value;
            }
        }
        
        public bool ForceSoftwareRendering { get; set; }

        protected float AnimationSpeedScale { get; set; } = 0.1f;
        
        protected ThemeVariant ActiveVariant { get; private set; }
        
        protected SukiColorTheme ActiveTheme { get; private set; }
        
        protected float AnimationSeconds => (float)_animationTick.Elapsed.TotalSeconds;
        
        private readonly Stopwatch _animationTick = new();
        private readonly bool _invalidateRect;

        protected EffectDrawBase(bool invalidateRect = true)
        {
            _invalidateRect = invalidateRect;
            var sTheme = SukiTheme.GetInstance();
            sTheme.OnBaseThemeChanged += v => ActiveVariant = v;
            ActiveVariant = sTheme.ActiveBaseTheme;
            sTheme.OnColorThemeChanged += t => ActiveTheme = t;
            ActiveTheme = sTheme.ActiveColorTheme!;
        }

        public override void OnRender(ImmediateDrawingContext context)
        {
            var leaseFeature = context.TryGetFeature<ISkiaSharpApiLeaseFeature>();
            if (leaseFeature is null) throw new InvalidOperationException("Unable to lease Skia API");
            using var lease = leaseFeature.Lease();
            var rect = SKRect.Create((float)EffectiveSize.X, (float)EffectiveSize.Y);
            if(lease.GrContext is null || ForceSoftwareRendering) // GrContext is null whenever there is no hardware acceleration available
                RenderSoftware(lease.SkCanvas, rect);
            else
                Render(lease.SkCanvas, rect);
        }
        
        public override void OnMessage(object message)
        {
            if (message == StartAnimations)
            {
                AnimationEnabled = true;
                RegisterForNextAnimationFrameUpdate();
            }
            else if (message == StopAnimations)
            {
                AnimationEnabled = false;
            }
            else if (message is SukiEffect effect)
            {
                Effect = effect;
            }
        }

        public override void OnAnimationFrameUpdate()
        {
            if (!AnimationEnabled) return;
            if(_invalidateRect)
                Invalidate(GetRenderBounds());
            else
                Invalidate();
            RegisterForNextAnimationFrameUpdate();
        }

        //protected abstract void InvalidateInternal();

        /// <summary>
        /// Called every frame to render content.
        /// </summary>
        protected abstract void Render(SKCanvas canvas, SKRect rect);
        
        /// <summary>
        /// Called every frame whenever the app falls back to software rendering (or <see cref="ForceSoftwareRendering"/> is enabled)
        /// </summary>
        protected abstract void RenderSoftware(SKCanvas canvas, SKRect rect);

        protected SKShader? EffectWithUniforms(float alpha = 1f) => 
            EffectWithUniforms(Effect, alpha);

        protected SKShader? EffectWithUniforms(SukiEffect? effect, float alpha = 1f) => 
            effect?.ToShaderWithUniforms(AnimationSeconds, ActiveVariant, GetRenderBounds(), AnimationSpeedScale, alpha);

        protected SKShader? EffectWithCustomUniforms(Func<SKRuntimeEffect,SKRuntimeEffectUniforms> uniformFactory, float alpha = 1f) =>
            EffectWithCustomUniforms(Effect, uniformFactory, alpha);
        
        protected SKShader? EffectWithCustomUniforms(SukiEffect? effect, Func<SKRuntimeEffect,SKRuntimeEffectUniforms> uniformFactory, float alpha = 1f) =>
            effect?.ToShaderWithCustomUniforms(uniformFactory, AnimationSeconds, GetRenderBounds(), AnimationSpeedScale, alpha);

        protected virtual void EffectChanged(SukiEffect? oldValue, SukiEffect? newValue)
        {
            // no-op
        }
        
        public virtual void Dispose()
        {
            // no-op
        }
        
        public virtual bool Equals(ICustomDrawOperation other) => false;
        
        public virtual bool HitTest(Point p) => false;
    }
}