text.glsl

// ---- text.vert.glsl
#version 150

uniform vec2 text_offset;
uniform vec2 rcp_screen_size;

in vec2 v_screen_pos;
in vec2 v_uv;
out vec2 f_uv;

void main() {
    f_uv = v_uv;
    gl_Position.xy = (v_screen_pos * rcp_screen_size) + text_offset;
    gl_Position.z = 0.0;
    gl_Position.w = 1.0;
}

// ---- text.frag.glsl

#version 150

uniform usampler2DRect tex;
uniform vec4 text_color_outer;
uniform vec4 text_color_inner;

in vec2 f_uv;
out vec4 out_color;

void main() {
    float v = float(texture(tex, f_uv).r) / 254.0;
    float a = clamp(2.0 * v, 0, 1);
    float c = clamp((v - 0.5) * 2.0, 0, 1);
    out_color = a * mix(text_color_outer, text_color_inner, c);
}