#version 330 core

#define FONT_WIDTH 128
#define FONT_HEIGHT 64
#define FONT_COLS 18
#define FONT_ROWS 7
#define FONT_CH_W (FONT_WIDTH  / FONT_COLS)
#define FONT_CH_H (FONT_HEIGHT / FONT_ROWS)
#define FONT_CH_W_UV (float(FONT_CH_W) / float(FONT_WIDTH))
#define FONT_CH_H_UV (float(FONT_CH_H) / float(FONT_HEIGHT))

uniform sampler2D font;
uniform float time;

flat in int glyph_c;
in vec4 glyph_fg_color;
in vec4 glyph_bg_color;
in vec2 uv;

float
map01(float x)
{
  return (x + 1) / 2;
}

void main() {
  int c = glyph_c;
  if ( ! (c >= 32 && c <= 126) ) {
    c = 63;
  }

  int index = c - 32;
  float x = float(index % FONT_COLS) * FONT_CH_W_UV;
  float y = float(index / FONT_COLS) * FONT_CH_H_UV;

  vec2 ch_size = vec2(FONT_CH_W_UV, -FONT_CH_H_UV);
  vec2 pos = vec2(x, y + FONT_CH_H_UV);
  vec2 uv_ = vec2(uv.x, uv.y);

  vec4 t = texture(font, pos + ch_size * uv_);
  gl_FragColor = glyph_bg_color * (1.0 - t.x) + t.x * glyph_fg_color
    * vec4(map01(sin(time)),
	   map01(cos(time)),
	   map01(sin(time)),
	   1);
}