GLSL: why is alpha value modifying RGB??

[hooyacrusty]

Hi,

I want to use a texture as a 2D vec4 array, without alpha effects, but I'm running into this problem where the sampled R,G, and B values are modified by the alpha value:

// to test, all colors in the texture image are (1,0,0,0.5)

vec4 color = texture2D(texture0,coords.st);

// result: color = (0.5,0,0,0.5)

--------------------------------------

// all colors in the texture image are (0,1,0,0.75)

vec4 color = texture2D(texture0,coords.st);

// result: color = (0,0.75,0,0.75)

--------------------------------------

what I want is the result to be the same as what I set in the texture image, not with the R,G, and B values modified.

Anyone have any ideas?

[Nowhere-01]

it's called blending and it is enabled by default. if you want pure output color while writing to alpha channel, you call glDisable(GL_BLEND); before rendering. and you call glEnable(GL_BLEND) if you want blending enabled again.

i think, you need to read some beginners OpenGL literature, it's not really an advanced question.

[hooyacrusty]

it makes no difference if i disable blending or not, the result is the same.

So if I disable blending and I still have the same issue is this still a beginner question?

[Nowhere-01]

where does this texture come from? if it's color is mixed with black(or whatever was in the background) using alpha value, it must be you using it as a framebuffer attachment and rendering to it with blending enabled. alpha-blending happens when texture is being rendered to, not when you are sampling it. so the problem lies at the stage, where that particular texture is filled.

[hooyacrusty]

Thanks Nowhere-01. I think maybe my problem has to do with premultiplication by alpha values possibly done in AWTTextureIO.