Start code re-work Advanced OpenGL chapter.

src/4.advanced_opengl/1.2.depth_testing_view/1.2.depth_testing.fs

@@ -0,0 +1,16 @@
+#version 330 core
+out vec4 FragColor;
+
+float near = 0.1; 
+float far = 100.0; 
+float LinearizeDepth(float depth) 
+{
+    float z = depth * 2.0 - 1.0; // back to NDC 
+    return (2.0 * near * far) / (far + near - z * (far - near));	
+}
+
+void main()
+{             
+    float depth = LinearizeDepth(gl_FragCoord.z) / far; // divide by far to get depth in range [0,1] for visualization purposes
+    FragColor = vec4(vec3(depth), 1.0);
+}