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gerrit-public.fairphone.software / platform / external / mesa3d / df2be226d9ca6772eb4615ce0670e66667b86691 / . / docs / shading.html
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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 Bollecd5c7c2012-06-12 09:05:03 +0200[diff] [blame]10<h1>Shading Language Support</h1>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]11
12<p>
13This page describes the features and status of Mesa's support for the
14<a href="http://opengl.org/documentation/glsl/" target="_parent">
15OpenGL Shading Language</a>.
16</p>
17
18<p>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]19Contents
20</p>
21<ul>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]22<li><a href="#envvars">Environment variables</a>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]23<li><a href="#120">GLSL 1.20 support</a>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]24<li><a href="#unsup">Unsupported Features</a>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]25<li><a href="#notes">Implementation Notes</a>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]26<li><a href="#hints">Programming Hints</a>
Brian Paul3bfedb72008-07-17 15:40:10 -0600[diff] [blame]27<li><a href="#standalone">Stand-alone GLSL Compiler</a>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]28<li><a href="#implementation">Compiler Implementation</a>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]29<li><a href="#validation">Compiler Validation</a>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]30</ul>
31
32
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]33
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]34<a name="envvars">
35<h2>Environment Variables</h2>
36
37<p>
38The <b>MESA_GLSL</b> environment variable can be set to a comma-separated
Brian Paul85fb3e42009-10-14 11:28:28 -0600[diff] [blame]39list of keywords to control some aspects of the GLSL compiler and shader
40execution. These are generally used for debugging.
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]41</p>
42<ul>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]43<li><b>dump</b> - print GLSL shader code to stdout at link time
44<li><b>log</b> - log all GLSL shaders to files.
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]45 The filenames will be "shader_X.vert" or "shader_X.frag" where X
46 the shader ID.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]47<li><b>nopt</b> - disable compiler optimizations
48<li><b>opt</b> - force compiler optimizations
49<li><b>uniform</b> - print message to stdout when glUniform is called
50<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]51 the vertex position with ftransform() and passes through the color and
52 texcoord[0] attributes.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]53<li><b>nopfrag</b> - force fragment shader to be a simple shader that passes
Brian Paul85fb3e42009-10-14 11:28:28 -0600[diff] [blame]54 through the color attribute.
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]55<li><b>useprog</b> - log glUseProgram calls to stderr
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]56</ul>
57<p>
58Example: export MESA_GLSL=dump,nopt
59</p>
60
61
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]62<a name="120">
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]63<h2>GLSL Version</h2>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]64
65<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]66The GLSL compiler currently supports version 1.20 of the shading language.
67</p>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]68
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]69<p>
70Several GLSL extensions are also supported:
71</p>
72<ul>
73<li>GL_ARB_draw_buffers
74<li>GL_ARB_texture_rectangle
75<li>GL_ARB_fragment_coord_conventions
76<li>GL_EXT_texture_array
77</ul>
Brian Paulc4341fe2008-12-15 18:30:40 -0700[diff] [blame]78
79
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]80<a name="unsup">
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]81<h2>Unsupported Features</h2>
82
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]83<p>XXX update this section</p>
84
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]85<p>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]86The following features of the shading language are not yet fully supported
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]87in Mesa:
88</p>
89
90<ul>
Brian Paul439909a2009-04-07 11:09:53 -0600[diff] [blame]91<li>Linking of multiple shaders does not always work. Currently, linking
92 is implemented through shader concatenation and re-compiling. This
93 doesn't always work because of some #pragma and preprocessor issues.
Brianb03e1712007-03-09 09:51:55 -0700[diff] [blame]94<li>gl_ClipVertex
Brian4b1d1b72007-04-27 15:25:00 -0600[diff] [blame]95<li>The gl_Color and gl_SecondaryColor varying vars are interpolated
96 without perspective correction
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]97</ul>
98
99<p>
100All other major features of the shading language should function.
101</p>
102
103
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]104<a name="notes">
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]105<h2>Implementation Notes</h2>
106
107<ul>
108<li>Shading language programs are compiled into low-level programs
109 very similar to those of GL_ARB_vertex/fragment_program.
Brianbbec2fd2007-01-28 12:11:10 -0700[diff] [blame]110<li>All vector types (vec2, vec3, vec4, bvec2, etc) currently occupy full
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]111 float[4] registers.
Brianbbec2fd2007-01-28 12:11:10 -0700[diff] [blame]112<li>Float constants and variables are packed so that up to four floats
113 can occupy one program parameter/register.
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]114<li>All function calls are inlined.
115<li>Shaders which use too many registers will not compile.
116<li>The quality of generated code is pretty good, register usage is fair.
117<li>Shader error detection and reporting of errors (InfoLog) is not
118 very good yet.
Brian05e6fd82007-03-27 16:05:25 -0600[diff] [blame]119<li>The ftransform() function doesn't necessarily match the results of
120 fixed-function transformation.
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]121</ul>
122
123<p>
124These issues will be addressed/resolved in the future.
125</p>
126
127
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]128<a name="hints">
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]129<h2>Programming Hints</h2>
130
131<ul>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]132<li>Use the built-in library functions whenever possible.
133 For example, instead of writing this:
134<pre>
135 float x = 1.0 / sqrt(y);
136</pre>
137 Write this:
138<pre>
139 float x = inversesqrt(y);
140</pre>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]141</li>
Brian9595d192007-01-20 13:40:57 -0700[diff] [blame]142</ul>
143
144
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]145<a name="standalone">
Brian Paul3bfedb72008-07-17 15:40:10 -0600[diff] [blame]146<h2>Stand-alone GLSL Compiler</h2>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]147
148<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]149The stand-alone GLSL compiler program can be used to compile GLSL shaders
150into low-level GPU code.
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]151</p>
152
153<p>
154This tool is useful for:
Andreas Bolldf2be222012-06-12 09:05:22 +0200[diff] [blame^]155</p>
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]156<ul>
157<li>Inspecting GPU code to gain insight into compilation
158<li>Generating initial GPU code for subsequent hand-tuning
159<li>Debugging the GLSL compiler itself
160</ul>
161
162<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]163After building Mesa, the compiler can be found at src/glsl/glsl_compiler
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]164</p>
165
166<p>
167Here's an example of using the compiler to compile a vertex shader and
168emit GL_ARB_vertex_program-style instructions:
169</p>
170<pre>
Sam Hocevarfde49432011-02-16 17:04:03 -0700[diff] [blame]171 src/glsl/glsl_compiler --dump-ast myshader.vert
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]172</pre>
173
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]174Options include
175<ul>
176<li><b>--dump-ast</b> - dump GPU code
177<li><b>--dump-hir</b> - dump high-level IR code
178<li><b>--dump-lir</b> - dump low-level IR code
179<li><b>--link</b> - ???
180</ul>
181
Brian61d31ae2007-02-17 09:41:19 -0700[diff] [blame]182
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]183
184
185<a name="implementation">
186<h2>Compiler Implementation</h2>
187
188<p>
189The source code for Mesa's shading language compiler is in the
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]190<code>src/glsl/</code> directory.
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]191</p>
192
193<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]194XXX provide some info about the compiler....
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]195</p>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]196
197<p>
198The final vertex and fragment programs may be interpreted in software
199(see prog_execute.c) or translated into a specific hardware architecture
200(see drivers/dri/i915/i915_fragprog.c for example).
201</p>
202
Brian8f9db0f2007-03-23 17:49:19 -0600[diff] [blame]203<h3>Code Generation Options</h3>
204
205<p>
206Internally, there are several options that control the compiler's code
207generation and instruction selection.
208These options are seen in the gl_shader_state struct and may be set
209by the device driver to indicate its preferences:
210
211<pre>
212struct gl_shader_state
213{
214 ...
215 /** Driver-selectable options: */
216 GLboolean EmitHighLevelInstructions;
217 GLboolean EmitCondCodes;
218 GLboolean EmitComments;
219};
220</pre>
221
222<ul>
223<li>EmitHighLevelInstructions
224<br>
225This option controls instruction selection for loops and conditionals.
226If the option is set high-level IF/ELSE/ENDIF, LOOP/ENDLOOP, CONT/BRK
227instructions will be emitted.
228Otherwise, those constructs will be implemented with BRA instructions.
229</li>
230
231<li>EmitCondCodes
232<br>
233If set, condition codes (ala GL_NV_fragment_program) will be used for
234branching and looping.
235Otherwise, ordinary registers will be used (the IF instruction will
236examine the first operand's X component and do the if-part if non-zero).
237This option is only relevant if EmitHighLevelInstructions is set.
238</li>
239
240<li>EmitComments
241<br>
242If set, instructions will be annoted with comments to help with debugging.
243Extra NOP instructions will also be inserted.
Andreas Bolldf2be222012-06-12 09:05:22 +0200[diff] [blame^]244</li>
Brian8f9db0f2007-03-23 17:49:19 -0600[diff] [blame]245</ul>
Brian07e62082007-02-27 16:45:40 -0700[diff] [blame]246
247
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]248<a name="validation">
249<h2>Compiler Validation</h2>
250
251<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]252Developers working on the GLSL compiler should test frequently to avoid
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]253regressions.
254</p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]255
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]256<p>
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]257The <a href="http://people.freedesktop.org/~nh/piglit/">Piglit</a> project
258has many GLSL tests and the
259<a href="http://glean.sf.net" target="_parent">Glean</a> glsl1 test
260tests GLSL features.
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]261</p>
262
Brian Paulf3ec1112010-08-24 09:02:05 -0600[diff] [blame]263<p>
264The Mesa demos repository also has some good GLSL tests.
265</p>
Brian7eba12e2007-03-28 17:14:35 -0600[diff] [blame]266
Andreas Bollecd5c7c2012-06-12 09:05:03 +0200[diff] [blame]267</body>
268</html>