Creating OpenGL Texture

I'm writing a pixel shader for a class, and the final step is to use a 1D texture to map whatever color the fragment would be under phong shading to another color to produce a banding effect. When I run the program the object appears completely black, so I think that I am creating the texture wrong. Here is the code to generate the texture

Code:

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// definitions actually located in a header file
#define COLOR_MAP_WIDTH 256
unsigned char color_map[COLOR_MAP_WIDTH][3];
#define RED_STEP 13
#define BLUE_STEP 27
#define GREEN_STEP 33
unsigned int color_map_id;

void gen_texture_map(void){
        int i;
        for(i = 0; i < 256; ++i){
                color_map[i][0] = (i/RED_STEP)*RED_STEP;
                color_map[i][1] = (i/GREEN_STEP)*GREEN_STEP;
                color_map[i][2] = (i/BLUE_STEP)*BLUE_STEP;
        }             

        glGenTextures(1, &color_map_id);
        glBindTexture(GL_TEXTURE_1D, color_map_id);
        glTexImage1D(GL_TEXTURE_1D, 0, 3, COLOR_MAP_WIDTH, 0, GL_RGB, GL_UNSIGNED_BYTE, color_map);
}

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It's a 1D, RGB texture with no border, so I think I have the glTexImage1D parameters right. When the object is drawn, I pass color_map_id to it as a sampler1D and perform a texture1D lookup with it. Am I setting it up wrong? Am I doing the lookup/id passing wrong? Why is the texture not loading? Thanks in advance for any help you can give

Code:

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(i/RED_STEP)*RED_STEP;

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I'm a little confused, you divide by RED_STEP and then multiply by it, leaving just i?

Apart from that, your texture generating looks fine to me.

PS, what does '3' as the 3rd argument to TexImage1D do? I use GL_RGB.

Quote:

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Originally Posted by Noise

Code:

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(i/RED_STEP)*RED_STEP;

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I'm a little confused, you divide by RED_STEP and then multiply by it, leaving just i?

Apart from that, your texture generating looks fine to me.

PS, what does '3' as the 3rd argument to TexImage1D do? I use GL_RGB.

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Those are integers, so it makes the values in the texture go up in steps. For example, if RED_STEP is 14, 0-13 maps to 0, 14-27 maps to 14, 28-41 maps to 28, etc.

I changed the 3 to GL_RGB, but still no luck. After looking at some tutorials, I changed the funciton to this

Code:

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void gen_texture_map(void){
        int i;
        for(i = 0; i < 256; ++i){
                color_map[i][0] = (i/RED_STEP)*RED_STEP;
                color_map[i][1] = (i/GREEN_STEP)*GREEN_STEP;
                color_map[i][2] = (i/BLUE_STEP)*BLUE_STEP;
        }             

        glEnable(GL_TEXTURE_1D);
        glGenTextures(1, &color_map_id);
        glBindTexture(GL_TEXTURE_1D, color_map_id);
        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
        glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
        glTexImage1D(GL_TEXTURE_1D, 0, GL_RGB, COLOR_MAP_WIDTH, 0, GL_RGB, GL_UNSIGNED_BYTE, color_map);
}

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And call glBindTexture(GL_TEXTURE_1D, color_map_id) before rendering the object. Still nothing

You will need those glTexParameteri calls to set those parameters for the texture, but you shouldn't need to do that other stuff. You would need to call glBindTexture before rendering if the active texture might have changed.

I believe that the problem is very likely elsewhere in the program.

I'm wondering if integer casting is screwing up your code. Try:

-ceil and floor functions
-manually put in (int) and (float) where you're casting

Those are the first few things I'd try.

Wait shouldn't color_map be a char array? Ints are 4 bytes long and chars are 1 byte, so it will sort of just be getting the first quarter of the array when you pass it to glTexImage1D. Make color_map an unsigned char.

Yeah good point, OpenGL expects it to be byte data based on this line's GL_UNSIGNED_BYTE

Code:

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glTexImage1D(GL_TEXTURE_1D, 0, 3, COLOR_MAP_WIDTH, 0, GL_RGB, GL_UNSIGNED_BYTE, color_map);

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color_map is declared as an unsigned char already.

>When I run the program the object appears completely black,

Can you see the object if you just color it (without texturing?). Maybe the object is not being drawn in a viewable area.

Oh yes sorry I was seeing color_map_id.

Yes you can see an object without texturing it. Unless there are no lights. I suggest turning both texturing and lighting off. Then if you still can't see it, it may be out of the camera's view so try turning the camera around.

Sorry for the late reply - this was due a while ago :D

Thanks for the suggestions all