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alpha texture

Started by kampfgnu Mar 21, 2009 at 8:04 AM 1 reply 550+ views

Original Post

Mar 21, 2009 at 8:04 AM

hello, how do i generate a texture only representing alphas by hand and load it? e.g. a 4x4 texture: float data[4*4] = [0.1, 0.1, 0.1, 0.1, 0.1, 0.5, 0.5, 0.1, 0.1, 0.5, 0.5, 0.1, 0.1, 0.1, 0.1, 0.1 ] defining it like that and then do:


glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, 4, 4, 0, GL_ALPHA, GL_FLOAT, &data);

seems not to work... anyone?

kampfgnu

Author

kampfgnu

Mar 21, 2009 at 8:40 AM

in comparison, if i create a float array with values like:

float data = [1,0,0,1, 1,0,0,1, 1,0,0,1,....]

and do a:

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, size, size, 0, GL_RGBA, GL_FLOAT, &data);

when drawing, it should be red, but also is not.
should this work, or am i on the totally wrong path?
greets

V-man

163

V-man

Mar 21, 2009 at 5:06 PM

It depends on lighting, the texture environment state.
If you use GL_ALPHA, it says

Quote:
Each element is a single alpha component.
The GL converts it to floating point and assembles it into an RGBA element
by attaching 0 for red, green, and blue.
Each component is then multiplied by the signed scale factor GL_c_SCALE,
added to the signed bias GL_c_BIAS,
and clamped to the range [0,1]
(see glPixelTransfer).

so the alpha will be right

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