text instancing

shaders/font.vert

@@ -0,0 +1,18 @@
+#version 330 core
+layout (location = 0) in vec2 vertex;
+
+// per instance
+layout (location = 1) in vec4 offset;
+layout (location = 2) in int tex_index;
+
+out vec2 v_TexCoords;
+uniform mat4 projection;
+uniform mat4 model;
+// buffer for all the 96 ascii characters' texcoords
+uniform vec2 texcoords[96 * 4];
+
+void main() {
+  vec2 pos = vec2((vertex.x) * offset.z, (vertex.y) * offset.w);
+  gl_Position = projection * model * vec4(pos + offset.xy, 0.0, 1.0);
+  v_TexCoords = texcoords[tex_index * 4 + gl_VertexID];
+}