[font.frag] Rainbow

shaders/font.frag

@@ -11,18 +11,26 @@
 
 uniform sampler2D font;
 uniform float time;
+uniform vec2 resolution;
 
 flat in int glyph_c;
 in vec4 glyph_fg_color;
 in vec4 glyph_bg_color;
 in vec2 uv;
 
-float
-map01(float x)
+float map01(float x)
 {
   return (x + 1) / 2;
 }
 
+vec3 hsl2rgb( in vec3 c )
+{
+    vec3 rgb = clamp( abs(mod(c.x*6.0+vec3(0.0,4.0,2.0),6.0)-3.0)-1.0,
+		      0.0, 1.0 );
+
+    return c.z + c.y * (rgb-0.5)*(1.0-abs(2.0*c.z-1.0));
+}
+
 void main() {
   int c = glyph_c;
   if ( ! (c >= 32 && c <= 126) ) {
@@ -38,9 +46,12 @@ void main() {
   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);
+
+  vec2 frag_uv = gl_FragCoord.xy / resolution;
+  vec4 rainbow = vec4(hsl2rgb(vec3((time + frag_uv.x + frag_uv.y) * 0.5,
+				   0.5,
+				   0.5)),
+		      1);
+
+  gl_FragColor = glyph_bg_color * (1.0 - t.x) + t.x * glyph_fg_color * rainbow;
 }