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gerrit-public.fairphone.software / platform / external / mesa3d / 85b66d20969685c26d3f7d22b6fc7b988872fa88 / . / 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
Timothy Arceria74300c2017-05-18 15:00:40 +1000[diff] [blame]53<li><b>cache_fb</b> - force cached shaders to be ignored and do a full
54 recompile via the fallback path</li>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]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>
Eleni Maria Stea9f59cb22017-08-04 20:20:12 +0300[diff] [blame]68Shaders can be dumped and replaced on runtime for debugging purposes. This
Tapani Pälli04e201d2015-08-31 09:54:23 +0300[diff] [blame]69feature is not currently supported by SCons build.
70
71This is controlled via following environment variables:
72<ul>
73<li><b>MESA_SHADER_DUMP_PATH</b> - path where shader sources are dumped
74<li><b>MESA_SHADER_READ_PATH</b> - path where replacement shaders are read
75</ul>
76Note, path set must exist before running for dumping or replacing to work.
77When both are set, these paths should be different so the dumped shaders do
Eleni Maria Stea9f59cb22017-08-04 20:20:12 +0300[diff] [blame]78not clobber the replacement shaders. Also, the filenames of the replacement shaders
79should match the filenames of the corresponding dumped shaders.
Tapani Pälli04e201d2015-08-31 09:54:23 +0300[diff] [blame]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>