Start preview feature. Add dummy triangle to test OpenGL.

resources/shaders/polygon.fs.glsl

@@ -0,0 +1,9 @@
+#version 330 core
+
+out vec4 FragColor;
+in  vec4 vertex_color;
+
+void main()
+{
+	FragColor = vertex_color;
+}

resources/shaders/polygon.vs.glsl

@@ -0,0 +1,12 @@
+#version 330 core
+
+//uniform mat4 mvp;
+uniform vec4 const_color;
+
+layout (location = 0) in vec2 input_vertex;
+out vec4 vertex_color;
+void main()
+{
+	gl_Position = vec4(input_vertex.x, input_vertex.y, 0.0, 1.0);
+	vertex_color = const_color;
+}