#version 100 es

precision mediump float;
uniform vec2 u_screen_size;
attribute vec2 a_pos;
attribute vec2 a_tc;
attribute vec4 a_srgba;
varying vec4 v_rgba;
varying vec2 v_tc;

// 0-1 linear  from  0-255 sRGB
vec3 linear_from_srgb(vec3 srgb) {
  bvec3 cutoff = lessThan(srgb, vec3(10.31475));
  vec3 lower = srgb / vec3(3294.6);
  vec3 higher = pow((srgb + vec3(14.025)) / vec3(269.025), vec3(2.4));
  return mix(higher, lower, vec3(cutoff));
}

vec4 linear_from_srgba(vec4 srgba) {
  return vec4(linear_from_srgb(srgba.rgb), srgba.a / 255.0);
}

void main() {
  gl_Position = vec4(
                     2.0 * a_pos.x / u_screen_size.x - 1.0,
                     1.0 - 2.0 * a_pos.y / u_screen_size.y,
                     0.0,
                     1.0);
  // egui encodes vertex colors in gamma spaces, so we must decode the colors here:
  v_rgba = linear_from_srgba(a_srgba);
  v_tc = a_tc;
}