I'm making a text renderer that uses FreeType 2 and legacy OpenGL. Problem is, FreeType 2's coordinate system has (0, 0) in the top left corner while OpenGL's coordinate system is Cartesian. This means I have to flip the bitmap. I expected glScalef to work with glBitmap but it has no effect. Can anyone tell me if it's possible to flip a bitmap vertically with glScalef, or if it is not possible, point me to some other source that can flip a bitmap upside down (Preferably efficiently as possible)?
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glScalef(1.0, -1.0, 1.0)
glBitmap(size_x, size_y, 0, 0, xadd, yadd, (GLubyte *) bitmap);
The function you are looking for is glPixelZoom.
Pixel zoom factors are not limited to positive values. Negative zoom factors reflect the resulting image about the current raster position.
It definitely will have the desired effect on glDrawPixels. There's a note in glBitmap saying that it acts like glDrawPixels but I cannot find any explicit statement on whether glPixelZoom applies to glBitmap or not, so YMMV.