Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / mesa3d / 8cad301a3ea4d2cf6297200f5eb5e229928b9120 / . / docs / shading.html
blob: 7e3d2e4fced0756509f861e4665fb6922c6039bb [file] [log] [blame]
Andreas Bollecd5c7c2012-06-12 09:05:03 +0200[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
2<html lang="en">
3<head>
4 <meta http-equiv="content-type" content="text/html; charset=utf-8">
5 <title>Shading Language Support</title>
6 <link rel="stylesheet" type="text/css" href="mesa.css">
7</head>
8<body>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]9
Andreas Bollb5da52a2012-09-18 18:57:02 +0200[diff] [blame]10<div class="header">
11 <h1>The Mesa 3D Graphics Library</h1>
12</div>
13
14<iframe src="contents.html"></iframe>
15<div class="content">
16
Andreas Bollecd5c7c2012-06-12 09:05:03 +0200[diff] [blame]17<h1>Shading Language Support</h1>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]18
19<p>
20This page describes the features and status of Mesa's support for the
Eric Engestrom30cf9ff2017-02-09 02:10:17 +0000[diff] [blame]21<a href="https://opengl.org/documentation/glsl/">
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]22OpenGL Shading Language</a>.
23</p>
24
25<p>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]26Contents
27</p>
28<ul>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]29<li><a href="#envvars">Environment variables</a>
Andreas Bolld4956692012-10-02 15:35:27 +0200[diff] [blame]30<li><a href="#support">GLSL 1.40 support</a>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]31<li><a href="#unsup">Unsupported Features</a>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]32<li><a href="#notes">Implementation Notes</a>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]33<li><a href="#hints">Programming Hints</a>
Brian Paul3bfedb72008-07-17 15:40:10 -0600[diff] [blame]34<li><a href="#standalone">Stand-alone GLSL Compiler</a>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]35<li><a href="#implementation">Compiler Implementation</a>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]36<li><a href="#validation">Compiler Validation</a>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]37</ul>
38
39
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]40<h2 id="envvars">Environment Variables</h2>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]41
42<p>
43The <b>MESA_GLSL</b> environment variable can be set to a comma-separated
Brian Paul85fb3e42009-10-14 11:28:28 -0600[diff] [blame]44list of keywords to control some aspects of the GLSL compiler and shader
45execution. These are generally used for debugging.
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]46</p>
47<ul>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]48<li><b>dump</b> - print GLSL shader code to stdout at link time
49<li><b>log</b> - log all GLSL shaders to files.
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]50 The filenames will be "shader_X.vert" or "shader_X.frag" where X
51 the shader ID.
Timothy Arceri30aa22d2016-07-08 12:44:44 +1000[diff] [blame]52<li><b>cache_info</b> - print debug information about shader cache
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]53<li><b>uniform</b> - print message to stdout when glUniform is called
54<li><b>nopvert</b> - force vertex shaders to be a simple shader that just transforms
Brian Paul85fb3e42009-10-14 11:28:28 -0600[diff] [blame]55 the vertex position with ftransform() and passes through the color and
56 texcoord[0] attributes.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]57<li><b>nopfrag</b> - force fragment shader to be a simple shader that passes
Brian Paul85fb3e42009-10-14 11:28:28 -0600[diff] [blame]58 through the color attribute.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]59<li><b>useprog</b> - log glUseProgram calls to stderr
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]60</ul>
61<p>
62Example: export MESA_GLSL=dump,nopt
63</p>
64
Tapani Pälli04e201d2015-08-31 09:54:23 +0300[diff] [blame]65<p>
66Shaders can be dumped and replaced on runtime for debugging purposes. Mesa
67needs to be configured with '--with-sha1' to enable this functionality. This
68feature is not currently supported by SCons build.
69
70This is controlled via following environment variables:
71<ul>
72<li><b>MESA_SHADER_DUMP_PATH</b> - path where shader sources are dumped
73<li><b>MESA_SHADER_READ_PATH</b> - path where replacement shaders are read
74</ul>
75Note, path set must exist before running for dumping or replacing to work.
76When both are set, these paths should be different so the dumped shaders do
77not clobber the replacement shaders.
78</p>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]79
Andreas Bolld4956692012-10-02 15:35:27 +0200[diff] [blame]80<h2 id="support">GLSL Version</h2>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]81
82<p>
Chris Forbesf6159af2013-11-24 17:44:06 +1300[diff] [blame]83The GLSL compiler currently supports version 3.30 of the shading language.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]84</p>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]85
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]86<p>
87Several GLSL extensions are also supported:
88</p>
89<ul>
90<li>GL_ARB_draw_buffers
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]91<li>GL_ARB_fragment_coord_conventions
Andreas Bolld4956692012-10-02 15:35:27 +0200[diff] [blame]92<li>GL_ARB_shader_bit_encoding
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]93</ul>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]94
95
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]96<h2 id="unsup">Unsupported Features</h2>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]97
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]98<p>XXX update this section</p>
99
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]100<p>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]101The following features of the shading language are not yet fully supported
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]102in Mesa:
103</p>
104
105<ul>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]106<li>Linking of multiple shaders does not always work. Currently, linking
107 is implemented through shader concatenation and re-compiling. This
108 doesn't always work because of some #pragma and preprocessor issues.
Brian4b1d1b72007-04-27 15:25:00 -0600[diff] [blame]109<li>The gl_Color and gl_SecondaryColor varying vars are interpolated
110 without perspective correction
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]111</ul>
112
113<p>
114All other major features of the shading language should function.
115</p>
116
117
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]118<h2 id="notes">Implementation Notes</h2>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]119
120<ul>
121<li>Shading language programs are compiled into low-level programs
122 very similar to those of GL_ARB_vertex/fragment_program.
Brianbbec2fd2007-01-28 12:11:10 -0700[diff] [blame]123<li>All vector types (vec2, vec3, vec4, bvec2, etc) currently occupy full
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]124 float[4] registers.
Brianbbec2fd2007-01-28 12:11:10 -0700[diff] [blame]125<li>Float constants and variables are packed so that up to four floats
126 can occupy one program parameter/register.
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]127<li>All function calls are inlined.
128<li>Shaders which use too many registers will not compile.
129<li>The quality of generated code is pretty good, register usage is fair.
130<li>Shader error detection and reporting of errors (InfoLog) is not
131 very good yet.
Brian05e6fd82007-03-27 16:05:25 -0600[diff] [blame]132<li>The ftransform() function doesn't necessarily match the results of
133 fixed-function transformation.
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]134</ul>
135
136<p>
137These issues will be addressed/resolved in the future.
138</p>
139
140
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]141<h2 id="hints">Programming Hints</h2>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]142
143<ul>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]144<li>Use the built-in library functions whenever possible.
145 For example, instead of writing this:
146<pre>
147 float x = 1.0 / sqrt(y);
148</pre>
149 Write this:
150<pre>
151 float x = inversesqrt(y);
152</pre>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]153</li>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]154</ul>
155
156
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]157<h2 id="standalone">Stand-alone GLSL Compiler</h2>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]158
159<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]160The stand-alone GLSL compiler program can be used to compile GLSL shaders
161into low-level GPU code.
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]162</p>
163
164<p>
165This tool is useful for:
Andreas Bolldf2be222012-06-12 09:05:22 +0200[diff] [blame]166</p>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]167<ul>
168<li>Inspecting GPU code to gain insight into compilation
169<li>Generating initial GPU code for subsequent hand-tuning
170<li>Debugging the GLSL compiler itself
171</ul>
172
173<p>
Elie TOURNIER5034cf42017-01-18 13:50:11 +0000[diff] [blame]174After building Mesa, the compiler can be found at src/compiler/glsl/glsl_compiler
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]175</p>
176
177<p>
178Here's an example of using the compiler to compile a vertex shader and
179emit GL_ARB_vertex_program-style instructions:
180</p>
181<pre>
Elie TOURNIER5034cf42017-01-18 13:50:11 +0000[diff] [blame]182 src/compiler/glsl/glsl_compiler --version XXX --dump-ast myshader.vert
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]183</pre>
184
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]185Options include
186<ul>
187<li><b>--dump-ast</b> - dump GPU code
188<li><b>--dump-hir</b> - dump high-level IR code
189<li><b>--dump-lir</b> - dump low-level IR code
Elie TOURNIER5034cf42017-01-18 13:50:11 +0000[diff] [blame]190<li><b>--dump-builder</b> - dump GLSL IR code
191<li><b>--link</b> - link shaders
192<li><b>--just-log</b> - display only shader / linker info if exist,
193without any header or separator
194<li><b>--version</b> - [Mandatory] define the GLSL version to use
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]195</ul>
196
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]197
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]198<h2 id="implementation">Compiler Implementation</h2>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]199
200<p>
201The source code for Mesa's shading language compiler is in the
Elie TOURNIER5034cf42017-01-18 13:50:11 +0000[diff] [blame]202<code>src/compiler/glsl/</code> directory.
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]203</p>
204
205<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]206XXX provide some info about the compiler....
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]207</p>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]208
209<p>
210The final vertex and fragment programs may be interpreted in software
211(see prog_execute.c) or translated into a specific hardware architecture
212(see drivers/dri/i915/i915_fragprog.c for example).
213</p>
214
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]215<h2 id="validation">Compiler Validation</h2>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]216
217<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]218Developers working on the GLSL compiler should test frequently to avoid
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]219regressions.
220</p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]221
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]222<p>
Eric Engestrom30cf9ff2017-02-09 02:10:17 +0000[diff] [blame]223The <a href="https://piglit.freedesktop.org/">Piglit</a> project
Andreas Bolld4956692012-10-02 15:35:27 +0200[diff] [blame]224has many GLSL tests.
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]225</p>
226
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]227<p>
228The Mesa demos repository also has some good GLSL tests.
229</p>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]230
Andreas Bollb5da52a2012-09-18 18:57:02 +0200[diff] [blame]231</div>
Andreas Bollecd5c7c2012-06-12 09:05:03 +0200[diff] [blame]232</body>
233</html>