HLSL Texture Samplers
Author
Does anyone know what value gets put into the alpha channel if you try sample a texture that doesn't have an alpha channel?
Eg. if I have a bitmap loaded in and I sample it in the shader with:
float4 tex = tex2D(TextureSampler, TextureCoords)
What gets put into tex.a? 0?
I ask because I want a good way to determine if in a specular map, the power/gloss value has been put into the alpha channel, and if not, use a default value.
I'm not sure, but I think this is one of the areas where no predictable behavior is guaranteed (like behavior when setting a texture to null). It might be a more robust option to convert your textures to use an alpha channel with the default value. That way you don't need extra code for special cases, which as I got told is always a good thing [smile]
To my knowledge, the behaviour is indeed specified. The default result of a texture access is (0, 0, 0, 1). So if you access a one-channel texture, you'll get (r, 0, 0, 1) as a result.
You might want to reread it in the documentation, though.
You might want to reread it in the documentation, though.
Author
Thanks. The documentation doesn't really specify what is returned.
http://msdn.microsoft.com/en-us/library/ee418491(VS.85).aspx
I guess I'll just have to test it out and see what happens.
http://msdn.microsoft.com/en-us/library/ee418491(VS.85).aspx
I guess I'll just have to test it out and see what happens.
Quote:Original post by Shael
I guess I'll just have to test it out and see what happens.
Unless you have every GPU and driver made in the last 7 years that you can test on, I wouldn't recommend that approach.
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