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151 lines
5.1 KiB
Plaintext
151 lines
5.1 KiB
Plaintext
TinyGL 0.4 (c) 1997-2002 Fabrice Bellard.
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General Description:
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--------------------
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TinyGL is intended to be a very small implementation of a subset of
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OpenGL* for embedded systems or games. It is a software only
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implementation. Only the main OpenGL calls are implemented. All the
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calls I considered not important are simply *not implemented*.
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The main strength of TinyGL is that it is fast and simple because it
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has not to be exactly compatible with OpenGL. In particular, the
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texture mapping and the geometrical transformations are very fast.
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The main features of TinyGL are:
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- Header compatible with OpenGL (the headers are adapted from the very good
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Mesa by Brian Paul et al.)
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- Zlib-like licence for easy integration in commercial designs (read
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the LICENCE file).
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- Subset of GLX for easy testing with X Window.
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- GLX like API (NGLX) to use it with NanoX in MicroWindows/NanoX.
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- Subset of BGLView under BeOS.
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- OpenGL like lightening.
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- Complete OpenGL selection mode handling for object picking.
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- 16 bit Z buffer. 16/24/32 bit RGB rendering. High speed dithering to
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paletted 8 bits if needed. High speed conversion to 24 bit packed
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pixel or 32 bit RGBA if needed.
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- Fast Gouraud shadding optimized for 16 bit RGB.
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- Fast texture mapping capabilities, with perspective correction and
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texture objects.
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- 32 bit float only arithmetic.
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- Very small: compiled code size of about 40 kB on x86. The file
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src/zfeatures.h can be used to remove some unused features from
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TinyGL.
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- C sources for GCC on 32/64 bit architectures. It has been tested
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succesfully on x86-Linux and sparc-Solaris.
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Examples:
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---------
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I took three simple examples from the Mesa package to test the main
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functions of TinyGL. You can link them to either TinyGL, Mesa or any
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other OpenGL/GLX implementation. You can also compile them with
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Microwindows.
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- texobj illustrates the use of texture objects. Its shows the speed
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of TinyGL in this case.
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- glutmech comes from the GLUT packages. It is much bigger and slower
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because it uses the lightening. I have just included some GLU
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functions and suppressed the GLUT related code to make it work. It
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shows the display list handling of TinyGL in particular. You can look
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at the source code to learn the keys to move the robot. The key 't'
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toggles between shaded rendering and wire frame.
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- You can download and compile the VReng project to see that TinyGL
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has been successfully used in a big project
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(http://www-inf.enst.fr/vreng).
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Architecture:
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-------------
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TinyGL is made up four main modules:
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- Mathematical routines (zmath).
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- OpenGL-like emulation (zgl).
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- Z buffer and rasterisation (zbuffer).
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- GLX interface (zglx).
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To use TinyGL in an embedded system, you should look at the GLX layer
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and modify it to suit your need. Adding a more user friendly
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developper layer (as in Mesa) may be useful.
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Notes - limitations:
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--------------------
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- See the file 'LIMITATIONS' to see the current functions supported by the API.
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- The multithreading could be easily implemented since no global state
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is maintainted. The library gets the current context with a function
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which can be modified.
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- The lightening is not very fast. I supposed that in most games the
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lightening is computed by the 3D engine.
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- Some changes are needed for 64 bit pointers for the handling of
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arrays of float with the GLParam union.
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- List sharing is partialy supported in the source, but not by the
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current TinyGLX implementation (is it really useful ?).
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- No user clipping planes are supported.
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- No color index mode (no longer useful !)
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- The mipmapping is not implemented.
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- The perspecture correction in the mapping code does not use W but
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1/Z. In any 'normal scene' it should work.
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- The resizing of the viewport in TinyGLX ensures that the width and
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the height are multiples of 4. This is not optimal because some pixels
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of the window may not be refreshed.
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Why ?
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-----
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TinyGL was developped as a student project for a Virtual Reality
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network system called VReng (see the VReng home page at
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http://www-inf.enst.fr/vreng).
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At that time (January 1997), my initial project was to write my own 3D
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rasterizer based on some old sources I wrote. But I realized that it
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would be better to use OpenGL to work on any platform. My problem was
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that I wanted to use texture mapping which was (and is still) quite
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slower on many software OpenGL implementation. I could have modified
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Mesa to suit my needs, but I really wanted to use my old sources for
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that project.
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I finally decided to use the same syntax as OpenGL but with my own
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libraries, thinking that later it could ease the porting of VReng to
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OpenGL.
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Now VReng is at last compatible with OpenGL, and I managed to patch
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TinyGL so that VReng can still work with it without any modifications.
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Since TinyGL may be useful for some people, especially in the world of
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embedded designs, I decided to release it 'as is', otherwise, it would
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have been lost on my hard disk !
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------------------------------------------------------------------------------
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* OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
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------------------------------------------------------------------------------
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Fabrice Bellard.
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