TinyGL: Documentation

General Description:

TinyGL is intended to be a very small implementation of a subset of OpenGL* for embedded systems or games. It is a software only implementation. Only the main OpenGL calls are implemented. All the calls I considered not important are simply not implemented.

The main strength of TinyGL is that it is fast and simple because it has not to be exactly compatible with OpenGL. In particular, the texture mapping and the geometrical transformations are very fast.

The main features of TinyGL are:

Header compatible with OpenGL (the headers are adapted from the very good Mesa by Brian Paul et al.)
Zlib-like licence for easy integration in commercial designs (read the LICENCE file).
Subset of GLX for easy testing with X Window.
GLX like API (NGLX) to use it with NanoX in MicroWindows/NanoX.
Subset of BGLView under BeOS.
OpenGL like lightening.
Complete OpenGL selection mode handling for object picking.
16 bit Z buffer. 16/24/32 bit RGB rendering. High speed dithering to paletted 8 bits if needed. High speed conversion to 24 bit packed pixel or 32 bit RGBA if needed.
Fast Gouraud shadding optimized for 16 bit RGB.
Fast texture mapping capabilities, with perspective correction and texture objects.
32 bit float only arithmetic.
Very small: compiled code size of about 40 kB on x86. The file src/zfeatures.h can be used to remove some unused features from TinyGL.
C sources for GCC on 32/64 bit architectures. It has been tested succesfully on x86-Linux and sparc-Solaris.

Examples:

I took three simple examples from the Mesa package to test the main functions of TinyGL. You can link them to either TinyGL, Mesa or any other OpenGL/GLX implementation. You can also compile them with Microwindows.

texobj illustrates the use of texture objects. Its shows the speed of TinyGL in this case.
glutmech comes from the GLUT packages. It is much bigger and slower because it uses the lightening. I have just included some GLU functions and suppressed the GLUT related code to make it work. It shows the display list handling of TinyGL in particular. You can look at the source code to learn the keys to move the robot. The key 't' toggles between shaded rendering and wire frame.
You can download and compile the VReng project to see that TinyGL has been successfully used in a big project (http://www-inf.enst.fr/vreng).

Architecture:

TinyGL is made up four main modules:

Mathematical routines (zmath).
OpenGL-like emulation (zgl).
Z buffer and rasterisation (zbuffer).
GLX interface (zglx).

To use TinyGL in an embedded system, you should look at the GLX layer and modify it to suit your need. Adding a more user friendly developper layer (as in Mesa) may be useful.

Notes - limitations:

See the file 'LIMITATIONS' to see the current functions supported by the API.
The multithreading could be easily implemented since no global state is maintainted. The library gets the current context with a function which can be modified.
The lightening is not very fast. I supposed that in most games the lightening is computed by the 3D engine.
Some changes are needed for 64 bit pointers for the handling of arrays of float with the GLParam union.
List sharing is partialy supported in the source, but not by the current TinyGLX implementation (is it really useful ?).
No user clipping planes are supported.
No color index mode (no longer useful !)
The mipmapping is not implemented.
The perspecture correction in the mapping code does not use W but 1/Z. In any 'normal scene' it should work.
The resizing of the viewport in TinyGLX ensures that the width and the height are multiples of 4. This is not optimal because some pixels of the window may not be refreshed.

Why ?

TinyGL was developped as a student project for a Virtual Reality network system called VReng (see the VReng home page at http://www-inf.enst.fr/vreng).

At that time (January 1997), my initial project was to write my own 3D rasterizer based on some old sources I wrote. But I realized that it would be better to use OpenGL to work on any platform. My problem was that I wanted to use texture mapping which was (and is still) quite slower on many software OpenGL implementation. I could have modified Mesa to suit my needs, but I really wanted to use my old sources for that project.

I finally decided to use the same syntax as OpenGL but with my own libraries, thinking that later it could ease the porting of VReng to OpenGL.

Now VReng is at last compatible with OpenGL, and I managed to patch TinyGL so that VReng can still work with it without any modifications.

Since TinyGL may be useful for some people, especially in the world of embedded designs, I decided to release it 'as is', otherwise, it would have been lost on my hard disk !

OpenGL(R) is a registered trademark of Silicon Graphics, Inc. ------------------------------------------------------------------------------ Fabrice Bellard.