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| author | Brian <brian@nostromo.localnet.net> | 2007-01-20 13:40:57 -0700 |
|---|---|---|
| committer | Brian <brian@nostromo.localnet.net> | 2007-01-20 13:40:57 -0700 |
| commit | 9595d1935c9934da60a09e659b6ea7d3b7d226e2 (patch) | |
| tree | 2882e0732983559efe7a66f44b442b905544d83f /docs/shading.html | |
| parent | 059e9014462fe5361055e529a344338dcbc43c5d (diff) | |
Added a page with shading language status, tips, etc.
Diffstat (limited to 'docs/shading.html')
| -rw-r--r-- | docs/shading.html | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/docs/shading.html b/docs/shading.html new file mode 100644 index 0000000000..e7c63d1dd2 --- /dev/null +++ b/docs/shading.html @@ -0,0 +1,116 @@ +<HTML> + +<TITLE>Shading Language Support</TITLE> + +<link rel="stylesheet" type="text/css" href="mesa.css"></head> + +<BODY> + +<H1>Shading Language Support</H1> + +<p> +This page describes the features and status of Mesa's support for the +<a href="http://opengl.org/documentation/glsl/" target="_parent"> +OpenGL Shading Language</a>. +</p> + +<p> +Last updated on 20 Jan 2007. +</p> + +<h2>Unsupported Features</h2> + +<p> +The following features of the shading language are not yet supported +in Mesa: +</p> + +<ul> +<li>Arrays +<li>Structs +<li>Linking of multiple shaders is not supported +<li>Noise functions +<li>Not all built-in OpenGL state variables are supported yet. + Common variables such as gl_ModelViewMatrix and gl_NormalMatrix + are supported. +<li>Integer operations are not fully implemented (most are implemented + as floating point). +</ul> + +<p> +All other major features of the shading language should function. +</p> + + +<h2>Implementation Notes</h2> + +<ul> +<li>Shading language programs are compiled into low-level programs + very similar to those of GL_ARB_vertex/fragment_program. +<li>All float/int/bool and vector types currently occupy full + float[4] registers. +<li>Float constants are packed so that up to four floats can occupy one + program parameter/register. +<li>All function calls are inlined. +<li>Shaders which use too many registers will not compile. +<li>The quality of generated code is pretty good, register usage is fair. +<li>Shader error detection and reporting of errors (InfoLog) is not + very good yet. +<li>There are massive memory leaks in the compiler. +</ul> + +<p> +These issues will be addressed/resolved in the future. +</p> + + +<h2>Programming Hints</h2> + +<ul> +<li>Always declare <em>in</em> function parameters as <em>const</em>. + This improves the efficiency of function inlining. +</li> +<br> +<li>To reduce register usage, declare variables within smaller scopes. + For example, the following code: +<pre> + void main() + { + vec4 a1, a2, b1, b2; + gl_Position = expression using a1, a2. + gl_Color = expression using b1, b2; + } +</pre> + Can be rewritten as follows to use half as many registers: +<pre> + void main() + { + { + vec4 a1, a2; + gl_Position = expression using a1, a2. + } + { + vec4 b1, b2; + gl_Color = expression using b1, b2; + } + } +</pre> + Alternately, rather than using several float variables, use + a vec4 instead. Use swizzling and writemasks to access the + components of the vec4 as floats. +</li> +<br> +<li>Use the built-in library functions whenever possible. + For example, instead of writing this: +<pre> + float x = 1.0 / sqrt(y); +</pre> + Write this: +<pre> + float x = inversesqrt(y); +</pre> +</ul> + + +</BODY> +</HTML> |