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gerrit-public.fairphone.software / platform / external / mesa3d / 6e44087e77f3ec6852d98bd6c6e89fcc23109943 / . / docs / shading.html
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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>nopt</b> - disable compiler optimizations
54<li><b>opt</b> - force compiler optimizations
55<li><b>uniform</b> - print message to stdout when glUniform is called
56<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]57 the vertex position with ftransform() and passes through the color and
58 texcoord[0] attributes.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]59<li><b>nopfrag</b> - force fragment shader to be a simple shader that passes
Brian Paul85fb3e42009-10-14 11:28:28 -0600[diff] [blame]60 through the color attribute.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]61<li><b>useprog</b> - log glUseProgram calls to stderr
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]62</ul>
63<p>
64Example: export MESA_GLSL=dump,nopt
65</p>
66
Tapani Pälli04e201d2015-08-31 09:54:23 +0300[diff] [blame]67<p>
68Shaders can be dumped and replaced on runtime for debugging purposes. Mesa
69needs to be configured with '--with-sha1' to enable this functionality. This
70feature is not currently supported by SCons build.
71
72This is controlled via following environment variables:
73<ul>
74<li><b>MESA_SHADER_DUMP_PATH</b> - path where shader sources are dumped
75<li><b>MESA_SHADER_READ_PATH</b> - path where replacement shaders are read
76</ul>
77Note, path set must exist before running for dumping or replacing to work.
78When both are set, these paths should be different so the dumped shaders do
79not clobber the replacement shaders.
80</p>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]81
Andreas Bolld4956692012-10-02 15:35:27 +0200[diff] [blame]82<h2 id="support">GLSL Version</h2>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]83
84<p>
Chris Forbesf6159af2013-11-24 17:44:06 +1300[diff] [blame]85The GLSL compiler currently supports version 3.30 of the shading language.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]86</p>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]87
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]88<p>
89Several GLSL extensions are also supported:
90</p>
91<ul>
92<li>GL_ARB_draw_buffers
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]93<li>GL_ARB_fragment_coord_conventions
Andreas Bolld4956692012-10-02 15:35:27 +0200[diff] [blame]94<li>GL_ARB_shader_bit_encoding
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]95</ul>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]96
97
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]98<h2 id="unsup">Unsupported Features</h2>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]99
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]100<p>XXX update this section</p>
101
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]102<p>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]103The following features of the shading language are not yet fully supported
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]104in Mesa:
105</p>
106
107<ul>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]108<li>Linking of multiple shaders does not always work. Currently, linking
109 is implemented through shader concatenation and re-compiling. This
110 doesn't always work because of some #pragma and preprocessor issues.
Brian4b1d1b72007-04-27 15:25:00 -0600[diff] [blame]111<li>The gl_Color and gl_SecondaryColor varying vars are interpolated
112 without perspective correction
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]113</ul>
114
115<p>
116All other major features of the shading language should function.
117</p>
118
119
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]120<h2 id="notes">Implementation Notes</h2>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]121
122<ul>
123<li>Shading language programs are compiled into low-level programs
124 very similar to those of GL_ARB_vertex/fragment_program.
Brianbbec2fd2007-01-28 12:11:10 -0700[diff] [blame]125<li>All vector types (vec2, vec3, vec4, bvec2, etc) currently occupy full
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]126 float[4] registers.
Brianbbec2fd2007-01-28 12:11:10 -0700[diff] [blame]127<li>Float constants and variables are packed so that up to four floats
128 can occupy one program parameter/register.
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]129<li>All function calls are inlined.
130<li>Shaders which use too many registers will not compile.
131<li>The quality of generated code is pretty good, register usage is fair.
132<li>Shader error detection and reporting of errors (InfoLog) is not
133 very good yet.
Brian05e6fd82007-03-27 16:05:25 -0600[diff] [blame]134<li>The ftransform() function doesn't necessarily match the results of
135 fixed-function transformation.
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]136</ul>
137
138<p>
139These issues will be addressed/resolved in the future.
140</p>
141
142
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]143<h2 id="hints">Programming Hints</h2>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]144
145<ul>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]146<li>Use the built-in library functions whenever possible.
147 For example, instead of writing this:
148<pre>
149 float x = 1.0 / sqrt(y);
150</pre>
151 Write this:
152<pre>
153 float x = inversesqrt(y);
154</pre>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]155</li>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]156</ul>
157
158
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]159<h2 id="standalone">Stand-alone GLSL Compiler</h2>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]160
161<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]162The stand-alone GLSL compiler program can be used to compile GLSL shaders
163into low-level GPU code.
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]164</p>
165
166<p>
167This tool is useful for:
Andreas Bolldf2be222012-06-12 09:05:22 +0200[diff] [blame]168</p>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]169<ul>
170<li>Inspecting GPU code to gain insight into compilation
171<li>Generating initial GPU code for subsequent hand-tuning
172<li>Debugging the GLSL compiler itself
173</ul>
174
175<p>
Elie TOURNIER5034cf42017-01-18 13:50:11 +0000[diff] [blame]176After building Mesa, the compiler can be found at src/compiler/glsl/glsl_compiler
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]177</p>
178
179<p>
180Here's an example of using the compiler to compile a vertex shader and
181emit GL_ARB_vertex_program-style instructions:
182</p>
183<pre>
Elie TOURNIER5034cf42017-01-18 13:50:11 +0000[diff] [blame]184 src/compiler/glsl/glsl_compiler --version XXX --dump-ast myshader.vert
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]185</pre>
186
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]187Options include
188<ul>
189<li><b>--dump-ast</b> - dump GPU code
190<li><b>--dump-hir</b> - dump high-level IR code
191<li><b>--dump-lir</b> - dump low-level IR code
Elie TOURNIER5034cf42017-01-18 13:50:11 +0000[diff] [blame]192<li><b>--dump-builder</b> - dump GLSL IR code
193<li><b>--link</b> - link shaders
194<li><b>--just-log</b> - display only shader / linker info if exist,
195without any header or separator
196<li><b>--version</b> - [Mandatory] define the GLSL version to use
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]197</ul>
198
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]199
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]200<h2 id="implementation">Compiler Implementation</h2>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]201
202<p>
203The source code for Mesa's shading language compiler is in the
Elie TOURNIER5034cf42017-01-18 13:50:11 +0000[diff] [blame]204<code>src/compiler/glsl/</code> directory.
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]205</p>
206
207<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]208XXX provide some info about the compiler....
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]209</p>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]210
211<p>
212The final vertex and fragment programs may be interpreted in software
213(see prog_execute.c) or translated into a specific hardware architecture
214(see drivers/dri/i915/i915_fragprog.c for example).
215</p>
216
Andreas Bollcc418882012-06-12 09:05:33 +0200[diff] [blame]217<h2 id="validation">Compiler Validation</h2>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]218
219<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]220Developers working on the GLSL compiler should test frequently to avoid
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]221regressions.
222</p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]223
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]224<p>
Eric Engestrom30cf9ff2017-02-09 02:10:17 +0000[diff] [blame]225The <a href="https://piglit.freedesktop.org/">Piglit</a> project
Andreas Bolld4956692012-10-02 15:35:27 +0200[diff] [blame]226has many GLSL tests.
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]227</p>
228
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]229<p>
230The Mesa demos repository also has some good GLSL tests.
231</p>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]232
Andreas Bollb5da52a2012-09-18 18:57:02 +0200[diff] [blame]233</div>
Andreas Bollecd5c7c2012-06-12 09:05:03 +0200[diff] [blame]234</body>
235</html>