BlazorBitmapRenderSurfaceAdapter.cs

using System.Runtime.InteropServices;
using Gondwana.Rendering;
using SkiaSharp;
 
namespace Gondwana.Blazor.Rendering;

public sealed class BlazorBitmapRenderSurfaceAdapter : RenderSurfaceAdapterBase, IDisposable
{
    private readonly BlazorBitmapRenderSurfaceComponent _component;
    private byte[]? _pixelBuffer;
    private bool _disposed;

    public BlazorBitmapRenderSurfaceAdapter(BlazorBitmapRenderSurfaceComponent component)
        : base(1, 1, initialSizeAvailable: false)
    {
        _component = component ?? throw new ArgumentNullException(nameof(component));
    }

    internal void UpdateSize(int width, int height)
    {
        SetDestinationSize(width, height);
    }

    public override void Present(SKImage bufferImage, SKRectI bufferRect, SKRect destRect)
    {
        if (_disposed)
        {
            bufferImage.Dispose();
            return;
        }
 
        var srcRect = SKRectI.Intersect(bufferRect, new SKRectI(0, 0, bufferImage.Width, bufferImage.Height));
        var w = srcRect.Width;
        var h = srcRect.Height;
        if (w <= 0 || h <= 0)
        {
            bufferImage.Dispose();
            return;
        }
 
        var needed = w * h * 4;
        if (_pixelBuffer == null || _pixelBuffer.Length != needed)
            _pixelBuffer = new byte[needed];
 
        var info = new SKImageInfo(w, h, SKColorType.Rgba8888, SKAlphaType.Unpremul);
 
        // Pin the managed array so we can pass its address to native SkiaSharp code.
        var gcHandle = GCHandle.Alloc(_pixelBuffer, GCHandleType.Pinned);
        bool success;
        try
        {
            success = bufferImage.ReadPixels(info, gcHandle.AddrOfPinnedObject(), w * 4, srcRect.Left, srcRect.Top);
        }
        finally
        {
            gcHandle.Free();
        }
 
        if (!success)
        {
            bufferImage.Dispose();
            return;
        }
 
        // In Blazor WASM (single-threaded) no copy is needed: the frame cannot be overwritten
        // before the queued InvokeAsync action consumes it. For Blazor Server the host is
        // expected to configure a separate loop, but the copy is omitted here for performance.
        _component.EnqueueFrame(_pixelBuffer, w, h, srcRect.Left, srcRect.Top, bufferImage.Width, bufferImage.Height);
 
        bufferImage.Dispose();
    }

    public void Dispose()
    {
        if (_disposed) return;
        _disposed = true;
        _pixelBuffer = null;
    }
}