spriteBatch =
new SpriteBatch(GraphicsDevice);
bs.AlphaSourceBlend =
Blend.SourceAlpha;
bs.AlphaDestinationBlend =
Blend.InverseSourceAlpha;
用XNA开发个编辑器，发现不能正确绘制PNG图片，所以需要AlphaBlend，于是写了上面的混合代码，但是我的电脑不支持HiDef，只能Reach，并提示“XNA Framework Reach profile does not support separate alpha blend. BlendState.ColorDestinationBlend and AlphaDestinationBlend must be set to the same value.”
折腾了几天，想到了用Shader解决，失败。
其实我一直以为Alpha混合要设置AlphaSource和AlphaDestination，但是我错了，主要应该设置ColorSourceBlend和ColorDestinationBlend：
spriteBatch =
new SpriteBatch(GraphicsDevice);
bs.ColorSourceBlend =
Blend.SourceAlpha;
bs.AlphaSourceBlend =
Blend.SourceAlpha;
bs.ColorDestinationBlend =
Blend.InverseSourceAlpha;
bs.AlphaDestinationBlend =
Blend.InverseSourceAlpha;
这样就可以得到很好的混合效果了，无论Reach或是HiDef。
