Write to one channel of R16G16 texture on Xbox

Question

I was going to draw my shadow map into one channel of a 16 bit texture and then draw a different shadow map into another channel of the same texture.

I realized that this might not be possible to do efficiently since my targetted hardware (Xbox) does not support blending R16G16 formats. (Although the HDRBlendable might make it possible if I need a blendable format to do this.)

Is it possible to mask one channel of a R16G16 texture on the Xbox? How do I do that?

Answer 1

No you can't mask a R16G16 channel in XNA.

You can do it with a blendable format though, in my case, to use floating point the best you can do is to use HDRBlendable (R10G10B10A2 on the Xbox), and set ColorWriteChannels in the blendstate used appropriately, e.g.:

    myBlendState = new BlendState() 
    { 
        AlphaSourceBlend = Blend.One, 
        ColorSourceBlend = Blend.One, 
        AlphaDestinationBlend = Blend.Zero, 
        ColorDestinationBlend = Blend.Zero, 
        ColorWriteChannels = ColorWriteChannels.Red 
    };