Tutorial for OpenGL?

[aqilc]

I'm a beginner in OpenGL, I don't use XLib at all, and this looks like a really nice alternative for the very heavy FreeType. I don't want to spend days/weeks learning XLib to figure out how to port either, so if you could provide a tutorial/demo for graphical OpenGL C programs, it would be extremely appreciated!!

[tomolt]

This is something I wanted to do for a while, I just haven't gotten around to it yet. But for the meantime, I can at least give you these tips:

• To display a glyph, you have to first draw it into a buffer in CPU memory with sft_render() and then upload that buffer into a GL Texture in GPU memory. You will also have to keep some additional information for each glyph around in CPU memory that tells you how big to render it and where to put the following glyphs etc. Simply storing the glyph's SFT_GMetrics should suffice, since all of that data is in there.
• To get things off the ground, you can initially put each glyph in a separate texture. Once it's working, you can optimize it by putting them all next to each other into a single GL_TEXTURE_2D (this is called a texture atlas). Alternatively, you could use a single GL_TEXTURE_2D_ARRAY, which is often easier to work with for these sorts of things.
• To upload libschrift-generated images to GL Textures, you can use glTexImage2D() or glTexSubImage2D() with format=GL_RED and type=GL_UNSIGNED_BYTE.
• OpenGL wants all its textures to have side lengths that are powers of two. The easiest way to achieve this with libschrift is to round up the glyph's width and height to powers of two before allocating the SFT_Image that you pass into sft_render().
• Since OpenGL expects its textures to have their first row at the bottom and their last row at the top, you should not set SFT_DOWNWARD_Y.
• To display text, you will of course need some kind of vertex and fragment shader (I'm assuming you're not using the old GL1.x fixed function pipeline since it's incredibly outdated). Since the texture is monochrome, it will have only a single color channel, which happens to be red. This means that your fragment shader will have to do something like gl_FragColor = texture(glyph_texture, my_texcoords).r * glyph_color;.