OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Buffers and Their Uses

An important goal of almost every graphics program is to draw pictures on the screen (or into an off-screen buffer). The framebuffer (which is most often the screen) is composed of a rectangular array of pixels, each capable of displaying a tiny square of color at that point in the image. After the rasterization stage, which is where the fragment shader was executed, the data are not pixels yet—just fragments. Each fragment has coordinate data that corresponds to a pixel, as well as color and depth values.

As shown in Figure 4.1, the lower-left pixel in an OpenGL window is pixel (0, 0), corresponding to the window coordinates of the lower-left corner of the 1 × 1 region occupied by this pixel. In general, pixel (x, y