PngReader.cs

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using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
 
namespace ReLogic.Content.Readers;
 
public class PngReader : IAssetReader, IDisposable
{
    private readonly GraphicsDevice _graphicsDevice;
 
    private readonly ThreadLocal<Color[]> _colorProcessingCache;
 
    private bool _disposedValue;
 
    public PngReader(GraphicsDevice graphicsDevice)
    {
        _graphicsDevice = graphicsDevice;
        _colorProcessingCache = new ThreadLocal<Color[]>();
    }
 
    public Type[] GetAssociatedTypes()
    {
        return new Type[1] { typeof(Texture2D) };
    }
 
    public async ValueTask<T> FromStream<T>(Stream stream, MainThreadCreationContext mainThreadCtx) where T : class
    {
        if (typeof(T) != typeof(Texture2D))
        {
            throw AssetLoadException.FromInvalidReader<PngReader, T>();
        }
        int width = default(int);
        int height = default(int);
        int len = default(int);
        IntPtr img = FNA3D.ReadImageStream(stream, ref width, ref height, ref len, -1, -1, false);
        PreMultiplyAlpha(img, len);
        await mainThreadCtx;
        Texture2D val = new Texture2D(_graphicsDevice, width, height);
        val.SetDataPointerEXT(0, (Rectangle?)null, img, len);
        FNA3D.FNA3D_Image_Free(img);
        return val as T;
    }
 
    protected virtual void Dispose(bool disposing)
    {
        if (!_disposedValue)
        {
            if (disposing)
            {
                _colorProcessingCache.Dispose();
            }
            _disposedValue = true;
        }
    }
 
    public void Dispose()
    {
        Dispose(disposing: true);
    }
 
    private unsafe static void PreMultiplyAlpha(IntPtr img, int len)
    {
        byte* colors = (byte*)img.ToPointer();
        for (int i = 0; i < len; i += 4)
        {
            int a = colors[i + 3];
            colors[i] = (byte)(colors[i] * a / 255);
            colors[i + 1] = (byte)(colors[i + 1] * a / 255);
            colors[i + 2] = (byte)(colors[i + 2] * a / 255);
        }
    }
}