Bufferless text rendering demo for OpenGL, inspired by the fullscreen quad method.
Each glyph bitmap is encoded in a 32-bit integer.
A string of N chars can therefore be stored in
uniform uint[N]. For each glyph, the vertex shader
arranges a quad on the fly, while the fragment shader
decodes the relevant bitmap from the uniform array.
All without the need for attribute buffers or textures.
The vertex shader arranges every
six consecutive vertices to a quad.
To render a sequence of N quads, call
glDrawArrays(GL_TRIANGLES, 0, N*6).
(1,1)
4--3 2
| / /|
|/ / |
5 0--1
(0,0)
0 1 2 3 4 5 vertex = gl_VertexID % 6
0 1 1 1 0 0 u = (0b001110 >> vertex) & 1
0 0 1 1 1 0 v = (0b011100 >> vertex) & 1
Each 32-bit integer represents 6 lines of 5 bits. The two remaining bits represent alternative quad configurations, to effectively draw a 5x7 bitmap.
00... 01... 10... 11... Upper 2 bits
LINE5 LINE0 LINE3
LINE4 LINE5 LINE5 LINE2
LINE3 LINE4 LINE4 LINE1
LINE2 LINE3 LINE3 LINE0 Lower 30 bits
LINE1 LINE2 LINE2 LINE0
LINE0 LINE1 LINE1 LINE5
LINE0 LINE0 LINE4
AB... gp... ({... j Target glyphs
The demo depends on SDL2 and OpenGL 3.3 Core. Initialize the build directory and compile the demo with:
cmake -B build
cmake --build build
Generate the integer literals with:
python3 font.py