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Reference Guide
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Reference Guide
Basic Information:
Before reading the following sections, here are some general pieces
of information which you should be aware of.
- Generic Function Naming:
- Many OpenGL procedures come in a variety
of forms, depending on the argument types. For example,
glVertex3f() takes 3 float arguments, glVertex4d()
takes 4 double arguments, and glVertex3iv() takes a
single pointer to an array of 3 int's. The naming
conventions are quite regular. These procedures are lumped
under the single name glVertex*() in the descriptions
below. See the reference manual for the actual calling
sequences.
- GL Data Types:
- OpenGL defines a number of data types. Most
of these translate directly to types in C or C++. For example,
GLdouble is the same as double, and GLuint is
an unsigned int. The type GLClampf is a float
that has been "clamped" to the interval [0,1], meaning that
values less than 0 are set to 0 and values greater than 1 are
set to 1. See the file Mesa/include/GL/gl.h for exact
type definitions.
- RGBA:
- OpenGL colors are typically defined using RGB (red,
green, blue) components and a special A (or alpha) component
The A component has varying interpretations depending on
context (typically in providing for transparency and color
blending). When no special effects are desired, set A = 1.
- Error Messages:
- OpenGL and Mesa are "quiet" about errors. When
an error has been committed, the system does not display any error
message. Rather it sets an error code, which the user can query
through glGetError(). It is the programmer's responsibility
to check the error code after each call to an OpenGL procedure.
If you are using Mesa (WAM and Glue), you can set the environment
variable MESA_DEBUG. This will cause Mesa to output a
message whenever an error is detected (and produces a few annoying
warning messages that you may not care about). This can be done by
adding the command "setenv MESA_DEBUG" to your login
initialization file.
By the way, Mesa always outputs a message about how many colors
from the colormap it was able to allocate. For best results,
kill any other colormap hogs (like netscape and xv) before
running any Mesa program.
Please report any errors or send comments to
Dave Mount
Last updated: Sat, Feb 8, 2003.