Windows and Coordinates

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___Screen Window ( TO BE )
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___Application Window (app window / window)
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     :.../gl_FragCoord (build-in variable in FragmentShader)

    URL: http://alfonse.bitbucket.org/oldtut/Basics/Tutorial%2002.html

gl_FragCoord is a built-in variable that is only available in a fragment shader. It is a vec3, so it has an X, Y, and Z component. The X and Y values are in window coordinates, so the absolute value of these numbers will change based on the window's resolution. Recall that window coordinates put the origin at the bottom-left corner. So fragments along the bottom of the triangle would have a lower Y value than those at the top.

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___Texture Coordinate ( TO BE )
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___OpenGL Coordinate ( TO BE )
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