Add two more examples

examples/checkers.frag

@@ -0,0 +1,39 @@
+#version 330
+
+out vec4 fragColor;
+
+uniform vec2 res;
+uniform float time;
+
+const float sharpness = 300;
+
+const float PI = 3.14159265358979323846;
+
+
+mat2 rot(float a) {
+        return mat2(
+                cos(a), -sin(a),
+                sin(a), cos(a)
+        );
+}
+
+void main(void) {
+        vec2 m = res/2;
+        float s = min(m.x, m.y);
+        vec2 p = (gl_FragCoord.xy - m) / s;
+
+        float repeat = 8.0;
+        float time_mod = mod(time / 200, repeat);
+        float w = 20 * pow(2, time_mod);
+
+        float f = time_mod / repeat;
+        vec2 pr = p * rot(f * PI/2);
+
+        float tp = mod(floor(log2(abs(pr.x/w)) + floor(log2(abs(pr.y/w)))), 2);
+
+        float darken = min(min(abs(pr.x), abs(pr.y)) / 0.01, 1.0);
+
+        float scene = tp * darken;
+
+        fragColor = vec4(vec3(1, 1, 1) * scene, 1);
+}

examples/symmetry.frag

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+#version 330
+
+out vec4 fragColor;
+
+uniform vec2 res;
+uniform float time;
+
+const float sharpness = 300;
+
+const float PI = 3.14159265358979323846;
+
+
+mat2 rot(float a) {
+        return mat2(
+                cos(a), -sin(a),
+                sin(a), cos(a)
+        );
+}
+
+float square(vec2 m, float a, float r, vec2 p) {
+        vec2 diff = abs((m - p) * rot(r));
+        float d = max(diff.x, diff.y);
+
+        return clamp((a - d)*sharpness, 0.0, 1.0);
+}
+
+void main(void) {
+        vec2 m = res/2;
+        float s = min(m.x, m.y);
+        vec2 p = (gl_FragCoord.xy - m) / s;
+
+        float scene = 0;
+
+        int n = 24;
+        for (int i = 0; i < n; i++) {
+                float c = square(vec2(0.5, 0) * rot(PI/2*(4.0*i/n)) * vec2(1, 1), 0.3, PI/2*(24.0*i/n - time/800), p);
+                scene = abs(scene - c);
+        }
+
+        fragColor = vec4(vec3(1, 1, 1) * scene, 1);
+}