单人游戏中的 AlphaMask 无法正常工作

Question

我正在尝试为战争迷雾示例构建渲染目标 alpha 蒙版。我告诉它我想用纯白色 (Alpha 255) 清除渲染目标

然后我用透明圆圈将我的图像绘制到 alpha 通道上，从那里我希望在渲染目标中有一个图像，其中有孔。然而事实并非如此。我非常熟悉 alpha 蒙版，并且在将单个图像绘制到 alpha 蒙版时已经成功地做到了这一点，但是当像我们这里一样绘制一堆时，它完全无法给我正确的 alpha 值.

if (mFogOfWarRT == null)
{
    mFogOfWarRT = new RenderTarget2D(pGraphics.GraphicsDevice, MapSize, MapSize);
    pGraphics.GraphicsDevice.SetRenderTarget(mFogOfWarRT);
    //pGraphicsDevice.Clear(Color.Black);
}
else
{
    pGraphics.GraphicsDevice.SetRenderTarget(mFogOfWarRT);
}

pGraphicsDevice.Clear(Color.White);
pSpriteBatch.Begin();
BlendState lKeep = new BlendState();
lKeep.AlphaSourceBlend = Blend.One;
lKeep.AlphaDestinationBlend = Blend.Zero;
lKeep.ColorSourceBlend = Blend.Zero;
lKeep.ColorDestinationBlend = Blend.One;
lKeep.ColorBlendFunction = BlendFunction.Subtract;
lKeep.AlphaBlendFunction = BlendFunction.Add;
pGraphicsDevice.BlendState = lKeep;
pGraphicsDevice.BlendState.ColorWriteChannels = ColorWriteChannels.Alpha;

foreach (ClearArea lArea in mDrawQueue)
{
    pSpriteBatch.Draw(mAlphaMask, new Rectangle((int)lArea.X, lArea.Y, lArea.Diameter, lArea.Diameter), Color.White);
}
//pSpriteBatch.Draw(mDot, new Rectangle(0, 0, 100, 100), Color.White);
pSpriteBatch.End();

pGraphicsDevice.SetRenderTarget(null);

这是我的 alpha 蒙版绘制代码。当绘制到屏幕上时，我们得到一个白色方块，没有别的。

在下面我将我的“地图”绘制为 RGB，然后设置 A，并绘制我的 alphamask 纹理，但它失败了

pGraphicsDevice.SetRenderTarget(null);

// Draw minimap texture
pGraphicsDevice.Clear(Color.CornflowerBlue);
pGraphicsDevice.BlendState = lKeep;
pGraphicsDevice.BlendState.ColorWriteChannels = ColorWriteChannels.Red | ColorWriteChannels.Blue | ColorWriteChannels.Green;

pSpriteBatch.Begin();
pSpriteBatch.Draw(mDot, new Rectangle(0, 0, 400, 400), Color.Blue);
pGraphicsDevice.BlendState.ColorWriteChannels = ColorWriteChannels.Alpha;
pSpriteBatch.Draw(mFogOfWarRT, Vector2.Zero, Color.White);

pSpriteBatch.End();

对此的任何帮助将不胜感激..

粘贴完整代码的bin

http://pastebin.com/KsEVaW0d

如果需要，可以提供结果的屏幕截图。

Answer 1

在我找到 Stencils 进行研究后，我决定 alpha 遮罩不是最好的方法。

下面的代码通过写入模板缓冲区解决了这个问题。

graphics.PreferredDepthStencilFormat = DepthFormat.Depth24Stencil8;
graphics.ApplyChanges();

AlphaTestEffect alphaTestEffect = new AlphaTestEffect(pGraphicsDevice);
alphaTestEffect.VertexColorEnabled = true;
alphaTestEffect.DiffuseColor = Color.White.ToVector3();
alphaTestEffect.AlphaFunction = CompareFunction.Equal;
alphaTestEffect.ReferenceAlpha = 0;
alphaTestEffect.World = Matrix.Identity;
alphaTestEffect.View = Matrix.Identity;
Matrix projection = Matrix.CreateOrthographicOffCenter(0, 400,400, 0, 0, 1);
alphaTestEffect.Projection = projection;
        // Create fog of war mask
        if (mFogOfWarRT == null)
        {
            mFogOfWarRT = new RenderTarget2D(pGraphics.GraphicsDevice, MapSize, MapSize, false, SurfaceFormat.Color, DepthFormat.Depth24Stencil8);
            pGraphics.GraphicsDevice.SetRenderTarget(mFogOfWarRT);

        }
        else
        {
            pGraphics.GraphicsDevice.SetRenderTarget(mFogOfWarRT);
        }
        //important both stencil states be created in their own object, cannot modify once set for some reason.
        DepthStencilState lState = new DepthStencilState();
        lState.StencilEnable = true;
        lState.StencilFunction = CompareFunction.Always;
        lState.ReferenceStencil = 1;
        lState.StencilPass = StencilOperation.Replace;
        lState.DepthBufferEnable = false;
        pGraphicsDevice.Clear(ClearOptions.Target | ClearOptions.Stencil,
                                  new Color(0, 0, 0, 1), 0, 0);
        pSpriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, null, lState, null, alphaTestEffect);
        foreach (ClearArea lArea in mDrawQueue)
        {
//draw whatever you want "visible" anything in the texture with an alpha of 0 will be allowed to draw.
            pSpriteBatch.Draw(mAlphaMask, new Rectangle((int)lArea.X, lArea.Y, lArea.Diameter, lArea.Diameter), Color.White);
        }

        pSpriteBatch.End();

        // Draw minimap texture
        DepthStencilState lState2 = new DepthStencilState();
        lState2.StencilEnable = true;
        lState2.StencilFunction = CompareFunction.Equal;
        lState2.ReferenceStencil = 0;
        lState2.StencilPass = StencilOperation.Keep;
        lState2.DepthBufferEnable = false;

        pSpriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, null, lState2, null);
        pSpriteBatch.Draw(mDot, new Rectangle(0, 0, 400, 400), Color.Black);

        pSpriteBatch.End();
        //done drawing to the render target
        pGraphicsDevice.SetRenderTarget(null);
        pGraphicsDevice.Clear(Color.Gray);
        pSpriteBatch.Begin();
        pSpriteBatch.Draw(mDot, new Rectangle(0, 0, 400, 400), Color.Blue);
        pSpriteBatch.Draw(mFogOfWarRT,Vector2.Zero,Color.White);
        pSpriteBatch.End();