Add slow and fast shaders.

Author: SuboptimalEng

08-checkerboard/shader.frag renamed to 08-checkerboard/fast-shader.frag

@@ -0,0 +1,41 @@
+precision mediump float;
+
+uniform float u_time;
+uniform vec2 u_resolution;
+
+// reference: https://iquilezles.org/articles/distfunctions2d/
+float sdBox(in vec2 p, in vec2 b) {
+  vec2 d = abs(p) - b;
+  return length(max(d, 0.0)) + min(max(d.x, d.y), 0.0);
+}
+
+void main() {
+  vec2 uv = 2.0 * gl_FragCoord.xy / u_resolution - 1.0;
+  uv.x = uv.x * u_resolution.x / u_resolution.y;
+
+  vec3 grey = vec3(0.5);
+  vec3 black = vec3(0.0);
+  vec3 white = vec3(1.0);
+
+  vec3 color = grey;
+
+  const float halfBoardSize = 4.0;
+  float boxWidth = 1.0 / (halfBoardSize * 4.0);
+  vec2 boxDimensions = vec2(boxWidth, boxWidth);
+  float separationSize = boxWidth + 0.01;
+
+  for (float i = -halfBoardSize; i <= halfBoardSize; i++) {
+    for (float j = -halfBoardSize; j <= halfBoardSize; j++) {
+      vec2 center = vec2(i, j) * (boxWidth + separationSize);
+      float distToBox = sdBox(uv - center, boxDimensions);
+
+      if (mod(i + j, 2.0) <= 0.01) {
+        color = distToBox < 0.0 ? white : color;
+      } else {
+        color = distToBox < 0.0 ? black : color;
+      }
+    }
+  }
+
+  gl_FragColor = vec4(color, 1.0);
+}