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## 1.5 Conventions

GLUT window and screen coordinates are expressed in pixels. The upper left hand corner of the screen or a window is (0,0). X coordinates increase in a rightward direction; Y coordinates increase in a downward direction. Note: This is inconsistent with OpenGL's coordinate scheme that generally considers the lower left hand coordinate of a window to be at (0,0) but is consistent with most popular window systems.

Integer identifiers in GLUT begin with one, not zero. So window identifiers, menu identifiers, and menu item indexes are based from one, not zero.

In GLUT's ANSI C binding, for most routines, basic types (`int`, `char*`) are used as parameters. In routines where the parameters are directly passed to OpenGL routines, OpenGL types (`GLfloat`) are used.

The header files for GLUT should be included in GLUT programs with the following include directive:

      #include <GL/glut.h>

Because a very large window system software vendor (who will remain nameless) has an apparent inability to appreciate that OpenGL's API is independent of their window system API, portable ANSI C GLUT programs should not directly include `<GL/gl.h>` or `<GL/glu.h>`. Instead, ANSI C GLUT programs should rely on `<GL/glut.h>` to include the necessary OpenGL and GLU related header files.

The ANSI C GLUT library archive is typically named `libglut.a` on Unix systems. GLUT programs need to link with the system's OpenGL and GLUT libraries (and any libraries these libraries potentially depend on). A set of window system dependent libraries may also be necessary for linking GLUT programs. For example, programs using the X11 GLUT implementation typically need to link with Xlib, the X extension library, possibly the X Input extension library, the X miscellaneous utilities library, and the math library. An example X11/Unix compile line would look like:

      cc -o foo foo.c -lglut -lGLU -lGL -lXmu -lXi -lXext -lX11 -lm

Next: 1.6 Terminology Up: 1 Introduction Previous: 1.4 API Version 3