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texture mapping and glColor() question


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#1 Thek   Members   -  Reputation: 122

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Posted 06 October 2001 - 05:50 PM

I''ve come across a strange problem when texture mapping that I can''t find a solution for anywhere on the net, so I thought I''d try here... An example of the problem: After I laod textures from a grassland tile-set (for a map editor I''m working on), I can''t change my glColor to anything but green or black. Specifically, any glColor() call short of the color black produces some shade of green. A call to glColor3f(1.0, 1.0, 1.0) should give me white, but instead gives a nice forest color... go figure. The tiles in the tile-set are all primarily green, and I''m sure the problem is related to this somehow, but I can''t figure out the relationship. My code works fine in all other respects. Is this problem too vague? Anyone have any ideas? Confused... Thek

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#2 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 06 October 2001 - 06:04 PM

Try making the tiles white and you should be able to color the tiles any way you like with glcolor. I think.

#3 Maximus   Members   -  Reputation: 124

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Posted 06 October 2001 - 06:05 PM

Think of it this way.. You have the colours of your texturemap. glColor functions multiply the pixels RGB channels by the RGB values specified. For instance you have a pixel of pure green (RGB 0,255,0) and you are using the colour white with glColor (glColor3f(1,1,1)), the output colours will be R 0*1 G 255*1 B 0*1, therefore the output is the same as the input colour in this case, pure green.

Now you want to make it all black? glColor3f(0,0,0) will give R 0*0 G 255*0 B 0*0, or each colour component will come out black.

One last example, the input textures pixel colour is RGB 132,23,212 (just random numbers i came up with), and you use glColor3f(0.2,0.4,0.6) (more random numbers), the output pixels colour will be R 132*0.2 G 23*0.4 B 212*0.6, or RGB 26.4,9.2,127.2

Hope that helps you understand the results you''re getting a bit better

#4 Thek   Members   -  Reputation: 122

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Posted 06 October 2001 - 06:15 PM

Thanks! I had read about OpenGL multiplying the color by the RGB of the textures, but hadn''t connected it to my problem. As I recall, there was something about having white borders around the image to allow for a full range of color... not sure about this, though. I should be able to clear things up now.
Just to get it straight... if I wanted to go back to a full range of drawing color without delving into borders, I could just make sure the last loaded texture was a solid white tile, right?
Thanks again,
Thek




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