freetype-gl | OpenGL text using one vertex buffer , one texture | Graphics library

According to the docs, FT_RENDER_MODE_MONO means you're rendering a monochrome bitmap using a one-bit-per-pixel format. This means that each byte of the bitmap you've just rendered two represents one row and 8 columns. In order to check if a pixel in column j is set in the bitmap, you must check the jth bit in a row.

off should now make more sense... i * slot->bitmap.pitch + j / 8 gets the offset of the byte in which your pixel lies. That's why it only increments by 1 for every 8 columns. You can't do memory reads and writes with offsets specified in bits, after all.

The test code you've provided, however, look like bit might be buggy. The second version uses 128, which has the binary representation of 10000000. The >> (x & 7) gets you each successive bit in turn, which can then be bitwise-anded with the byte in which the pixel lies to check if the pixel is actually turned on. The first version of your code has 0xC0 instead, which has bitwise representation 11000000, and so the test isn't actually doing what you want at all (it is checking if the j th and j+1 th pixels are set, unless j % 8 is 7)