How can I render text with modern OpenGL and stb_truetype, and why are the loaded textures black?

Question

I've spent the past couple of days just desperately trying to get stb_truetype to render anything using the simple example provided https://github.com/nothings/stb/blob/master/stb_truetype.h#L242-L281, however, no matter what I tried, the texture being loaded always ends up being completely black.

I've tried writing the generated texture data back to a .png file as

lodepng::encode("foopng", temp_bitmap, 512, 512, LCT_GREY);

and the font actually gets rendered properly

However, when I inspect the loaded texture in Nsight (or CodeXL), it looks completely black, and upon inspection of the actual data in the texture in CodeXL, it shows zeros basically everywhere, except for one small blob of a few non-zero numbers (which is nothing like the saved PNG).

I also tried changing to a different font and the generated quad geometry does change, as do the generated texture coordintes by stbtt_GetBakedQuad(...) (I even tried to manually set the texture coordinates all the way from 0 to 1 on the edges of the quad).

I'm not sure if it's CodeXL and Nsight both mis-interpreting the contents of the texture, even though the data view in the screenshot shows each byte, but when rendering I also get everything rendered with this texture completely black.

Is the texture being loaded incorrectly, or am I doing something else wrong? I'm using OpenGL 4.4.

Answer 1

Recently I've had the same problem using LWJGL/STB and modern OpenGL.

Changing font texture format helped in my case. Try changing:

glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, 512,512, 0, GL_ALPHA, GL_UNSIGNED_BYTE, temp_bitmap);

to:

glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, 512,512, 0, GL_RED, GL_UNSIGNED_BYTE, temp_bitmap);

I think it works same way as

lodepng::encode("foopng", temp_bitmap, 512, 512, LCT_GREY);

did, representing the alpha value as GREY(RED) color.