TransitionBlendGpu.cs

public class TransitionBlendGpu
{
	GraphicsDevice GraphicsDevice;
	SpriteBatch SpriteBatch;
	BlendState BlendAlpha1;
	BlendState BlendAlphaAdd;
	BlendState BlendAlphaSub;
	Texture2D DummyTexture;

	public TransitionBlendGpu(GraphicsDevice GraphicsDevice)
	{
		this.GraphicsDevice = GraphicsDevice;
		this.SpriteBatch = new SpriteBatch(GraphicsDevice);
		this.DummyTexture = new Texture2D(GraphicsDevice, 1, 1);
		this.DummyTexture.SetData(new Color[] { Color.White });

		BlendAlpha1 = new BlendState();
		BlendAlpha1.ColorWriteChannels = ColorWriteChannels.Alpha;
		BlendAlpha1.AlphaDestinationBlend = BlendAlpha1.ColorDestinationBlend = Blend.Zero;
		BlendAlpha1.AlphaSourceBlend = BlendAlpha1.ColorSourceBlend = Blend.One;
		BlendAlpha1.AlphaBlendFunction = BlendAlpha1.ColorBlendFunction = BlendFunction.Add;

		BlendAlphaSub = new BlendState();
		BlendAlphaSub.ColorWriteChannels = ColorWriteChannels.Alpha;
		BlendAlphaSub.AlphaDestinationBlend = BlendAlphaSub.ColorDestinationBlend = Blend.DestinationAlpha;
		BlendAlphaSub.AlphaSourceBlend = BlendAlphaSub.ColorSourceBlend = Blend.SourceAlpha;
		BlendAlphaSub.AlphaBlendFunction = BlendAlphaSub.ColorBlendFunction = BlendFunction.ReverseSubtract;

		BlendAlphaAdd = new BlendState();
		BlendAlphaAdd.ColorWriteChannels = ColorWriteChannels.Alpha;
		BlendAlphaAdd.AlphaDestinationBlend = BlendAlphaAdd.ColorDestinationBlend = Blend.DestinationAlpha;
		BlendAlphaAdd.AlphaSourceBlend = BlendAlphaAdd.ColorSourceBlend = Blend.SourceAlpha;
		BlendAlphaAdd.AlphaBlendFunction = BlendAlphaAdd.ColorBlendFunction = BlendFunction.Add;
	}


	public Texture2D GenerateAlpha(int Width, int Height)
	{
		var AlphaTexture = new Texture2D(GraphicsDevice, Width, Height);
		var WidthHeight = Width * Height;
		var Data = new RGBA[WidthHeight];
		for (int n = 0, y = 0; y < Height; y++)
		{
			for (int x = 0; x < Width; x++)
			{
				Data[n].A = (byte)(x * 255 / Width);
				n++;
			}
		}
		AlphaTexture.SetData(Data);
		return AlphaTexture;
	}

	public Texture2D GenerateAlphaFromRedChannel(Texture2D BaseImage)
	{
		return GenerateAlphaFromRedChannel(BaseImage, false);
	}

	public Texture2D GenerateAlphaFromRedChannel(Texture2D BaseImage, bool DisposeBaseImage)
	{
		var Width = BaseImage.Width;
		var Height = BaseImage.Height;
		var AlphaTexture = new Texture2D(GraphicsDevice, Width, Height);
		var WidthHeight = Width * Height;
		var Data = new RGBA[WidthHeight];
		BaseImage.GetData(Data);
		{
			for (int n = 0, y = 0; y < Height; y++)
			{
				for (int x = 0; x < Width; x++)
				{
					Data[n].A = Data[n].R;
					Data[n].R = 0;
					Data[n].G = 0;
					Data[n].B = 0;
					n++;
				}
			}
		}
		AlphaTexture.SetData(Data);
		if (DisposeBaseImage) BaseImage.Dispose();
		return AlphaTexture;
	}

	public void CombineAlpha(RenderTarget2D RenderTarget, Texture2D TextureColor, Texture2D TextureAlpha, float Step)
	{
		int Width = TextureColor.Width;
		int Height = TextureColor.Height;

		var GraphicsDevice = RenderTarget.GraphicsDevice;

		var OldRenderTargets = GraphicsDevice.GetRenderTargets();
		GraphicsDevice.SetRenderTarget(RenderTarget);
		{
			SpriteBatch.Begin(SpriteSortMode.Immediate, BlendState.Opaque);
			{
				SpriteBatch.Draw(TextureColor, new Vector2(0, 0), Color.White);
			}
			SpriteBatch.End();
		}
		{
			float AlphaSub = MathHelper.Clamp(1.0f - Step * 2.0f, 0.0f, 1.0f);
			float AlphaAdd = MathHelper.Clamp(Step * 2.0f - 1.0f, 0.0f, 1.0f);

			{
				SpriteBatch.Begin(SpriteSortMode.Immediate, BlendAlpha1);
				{
					SpriteBatch.Draw(
					 TextureAlpha,
					 Vector2.Zero,
					 Color.White
					);
				}
				SpriteBatch.End();
			}
			if (AlphaSub > 0)
			{
				SpriteBatch.Begin(SpriteSortMode.Immediate, BlendAlphaSub);
				{
					SpriteBatch.Draw(DummyTexture, new Rectangle(0, 0, Width, Height), new Color(AlphaSub, AlphaSub, AlphaSub, AlphaSub));
				}
				SpriteBatch.End();
			}
			if (AlphaAdd > 0)
			{
				SpriteBatch.Begin(SpriteSortMode.Immediate, BlendAlphaAdd);
				{
					SpriteBatch.Draw(DummyTexture, new Rectangle(0, 0, Width, Height), new Color(AlphaAdd, AlphaAdd, AlphaAdd, AlphaAdd));
				}
				SpriteBatch.End();
			}
		}
		GraphicsDevice.SetRenderTargets(OldRenderTargets);
	}
}