feat: mat2 glsl helpers with tests.

src/lib/shaders/includes/math/mat2.glsl

@@ -0,0 +1,13 @@
+#pragma once
+
+mat2 mat2Identity() {
+  return mat2( 1., 0., 0., 1. );
+}
+
+// https://thebookofshaders.com/08/
+mat2 mat2Rotate(float angle){
+  float c = cos(angle);
+  float s = sin(angle);
+
+  return mat2( c, -s, s, c );
+}

src/lib/shaders/includes/math/mat2.test.glsl

@@ -0,0 +1,32 @@
+#pragma include <tests/fragment>
+#pragma include "mat2"
+
+void testMatEquals( inout TestSuite suite, int id, mat2 m, mat2 target ) {
+  for( int i = 0; i < 2; i ++ ) {
+    for( int j = 0; j < 2; j ++ ) {
+      assert( suite, id + i*2 + j, m[i][j] == target[i][j] );
+    }
+  }
+}
+
+void tests( inout TestSuite suite ) {
+
+  mat2 uninitialized;
+
+  mat2 zero = mat2( 0., 0., 0., 0. );
+  testMatEquals( suite, 10, uninitialized, zero );
+
+  mat2 reference = mat2( 0., 1., 2., 3. );
+
+  mat2 refByIdentity = reference * mat2Identity();
+  testMatEquals( suite, 30, refByIdentity, reference );
+
+  mat2 vec = mat2( vec2( 0., 1. ), vec2( 2., 3. ) );
+  testMatEquals( suite, 40, vec, reference );
+
+  mat2 manual;
+  manual[0] = vec2( 0., 1. );
+  manual[1].yx = vec2( 3., 2. );
+  testMatEquals( suite, 50, manual, reference );
+
+}