fixed minor regression, cleaned up source tree

resources/shaders/color-passthrough.vertex

@@ -0,0 +1,13 @@
+#version 450
+layout(location = 0) in vec2 position;
+layout(location = 1) in vec4 color;
+
+layout(location = 0) out vec2 tex_coords;
+layout(location = 1) out vec4 out_color;
+
+void main() {
+    out_color = color;
+
+    gl_Position = vec4(position, 0.0, 1.0);
+    tex_coords = position;
+}