Question

Please help me understand what the following is doing. Specifically, what is variable ‘c’, and what is the third array dimension for (isn’t an image a 2-dimensional pixel rectangle)?
I’ll post a link to this code if context is needed, but the context in general is mapping this checkerboard pattern to a rotating cube.

GLubyte image[TextureSize][TextureSize][3];
GLubyte image2[TextureSize][TextureSize][3];

// Create a checkerboard pattern
for ( int i = 0; i < 64; i++ ) {
    for ( int j = 0; j < 64; j++ ) {
        GLubyte c = (((i & 0x8) == 0) ^ ((j & 0x8)  == 0)) * 255;
        image[i][j][0]  = c;
        image[i][j][1]  = c;
        image[i][j][2]  = c;
        image2[i][j][0] = c;
        image2[i][j][1] = 0;
        image2[i][j][2] = c;
    }
}

Answer 1

An image is 2 spatial dimensions and color – so 3 dimensions in a way.
The last [] is the red,green,blue pixel values

This is just using the ‘c’ array syntax to do the calculations into the memory for you.

The layout in memory is just
[row1][col1][red], [row1][col1][green], [row1][col1][blue], [row1][col2][red], [row1][col2][green], [row1][col2][blue] ........

So if c is either 0 or 255 then

// sets all red,green,blue to same value = black (c=0) or white (c=255)
image[i][j][0]  = c;
image[i][j][1]  = c;
image[i][j][2]  = c;

// sets red and blue on but green off = purple
image[i][j][0]  = c;
image[i][j][1]  = 0;
image[i][j][2]  = c;