First edit for framebuffers but it's slapped together and doesn't work yet.

21-framebuffers/shaders/21-screen.vert.glsl

@@ -0,0 +1,11 @@
+#version 330 core
+layout (location = 0) in vec2 aPos;
+layout (location = 1) in vec2 aTexCoords;
+
+out vec2 TexCoords;
+
+void main()
+{
+    gl_Position = vec4(aPos.x, aPos.y, 0.0, 1.0);
+    TexCoords = aTexCoords;
+}