utils: added translation and box shape

utilities/shapes.glsl

@@ -5,6 +5,14 @@ vec3 circle(in vec2 _st, in float _radius, vec3 color){
                          dot(dist,dist)*4.0);
 }
 
+vec3 box(vec2 width, vec2 height) {
+    height = vec2(0.5) - height*0.5;
+    vec2 he = height+0.001;
+    vec2 uv = smoothstep(height, he, width);
+    uv *= smoothstep(height, he, vec2(1.0)-width);
+    return vec3(uv.x*uv.y);
+}
+
 // Inspired by (but modified)
 // http://thndl.com/square-shaped-shaders.html
 #define TAU 6.28318530718

utilities/translation.glsl

@@ -0,0 +1,8 @@
+mat2 rotate2d(float a) {
+    float c = cos(a);
+    return mat2(c, -sin(a), sin(a), c);
+}
+
+mat2 scale(vec2 s) {
+    return mat2(s.x, 0., 0., s.y);
+}