renderer refactoring done

internal/renderer/shaders/triangle.vert

@@ -0,0 +1,12 @@
+#version 450
+
+// Fullscreen triangle, no vertex buffer. One triangle covers the viewport.
+vec2 positions[3] = vec2[](
+    vec2(-1.0, -1.0),
+    vec2( 3.0, -1.0),
+    vec2(-1.0,  3.0)
+);
+
+void main() {
+    gl_Position = vec4(positions[gl_VertexIndex], 0.0, 1.0);
+}