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Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]1<html>
2
3<title>Mesa EGL</title>
4
5<head><link rel="stylesheet" type="text/css" href="mesa.css"></head>
6
7<body>
8
9<h1>Mesa EGL</h1>
10
11<p>The current version of EGL in Mesa implements EGL 1.4. More information
12about EGL can be found at
Brian Paulaeff9f92010-01-21 08:13:32 -0700[diff] [blame]13<a href="http://www.khronos.org/egl/" target="_parent">
14http://www.khronos.org/egl/</a>.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]15
16<p>The Mesa's implementation of EGL uses a driver architecture. The main
17library (<code>libEGL</code>) is window system neutral. It provides the EGL
18API entry points and helper functions for use by the drivers. Drivers are
19dynamically loaded by the main library and most of the EGL API calls are
20directly dispatched to the drivers.</p>
21
22<p>The driver in use decides the window system to support. For drivers that
23support hardware rendering, there are usually multiple drivers supporting the
24same window system. Each one of of them supports a certain range of graphics
25cards.</p>
26
27<h2>Build EGL</h2>
28
29<ol>
30<li>
Jeff Smithfab1f072008-06-13 09:50:43 -0500[diff] [blame]31<p>Run <code>configure</code> with the desired state trackers and enable
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]32the Gallium driver for your hardware. For example</p>
33
34<pre>
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]35 $ ./configure --enable-gles-overlay --with-state-trackers=egl,vega --enable-gallium-{swrast,intel}
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]36</pre>
37
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]38<p>The main library and OpenGL is enabled by default. The first option enables
39<a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The <code>egl</code> state
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]40tracker is needed by a number of EGL drivers. EGL drivers will be covered
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]41later. The <a href="openvg.html">vega state tracker</a> provides OpenVG
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]421.x.</p>
43</li>
44
45<li>Build and install Mesa as usual.</li>
46</ol>
47
48<p>In the given example, it will build and install <code>libEGL</code>,
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]49<code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>,
50<code>libOpenVG</code>, and one or more EGL drivers.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]51
52<h3>Configure Options</h3>
53
54<p>There are several options that control the build of EGL at configuration
55time</p>
56
57<ul>
58<li><code>--enable-egl</code>
59
60<p>By default, EGL is enabled. When disabled, the main library and the drivers
61will not be built.</p>
62
63</li>
64
Chia-I Wua6342af2010-01-26 10:54:45 +0800[diff] [blame]65<li><code>--with-egl-driver-dir</code>
66
67<p>The directory EGL drivers should be installed to. If not specified, EGL
68drivers will be installed to <code>${libdir}/egl</code>.</p>
69
70</li>
71
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]72<li><code>--with-egl-platforms</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]73
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]74<p>List the native platform window system(s) to support. It is by default
75<code>x11</code>, which supports the X Window System. Its argument is a comma
76separated string like, for example, <code>--with-egl-platforms=x11,kms</code>.
77Because an EGL driver decides which window system to support, this example will
78enable two (sets of) EGL drivers. One supports the X window system and the
79other supports bare KMS (kernel modesetting).</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]80
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]81<p>The available platforms are <code>x11</code>, <code>kms</code>,
82<code>fbdev</code>, and <code>gdi</code>. The <code>gdi</code> platform can
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]83only be built with SCons.</p>
84
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]85</li>
86
87<li><code>--with-state-trackers</code>
88
89<p>The argument is a comma separated string. It is usually used to specify the
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]90rendering APIs, such as OpenVG, to build. But it should be noted that a number
91of EGL drivers depend on the <code>egl</code> state tracker. They will
92<em>not</em> be built without the <code>egl</code> state tracker.</p>
93
94</li>
95
96<li><code>--enable-gles-overlay</code>
97
98<p>OpenGL and OpenGL ES are not controlled by
99<code>--with-state-trackers</code>. OpenGL is always built. To build OpenGL
100ES, this option must be explicitly given.</p>
101
102</li>
103
104<li><code>--enable-gles1</code> and <code>--enable-gles2</code>
105
106<p>Unlike <code>--enable-gles-overlay</code>, which builds one library for each
107rendering API, these options enable OpenGL ES support in OpenGL. The result is
108one big library that supports multiple APIs. This is used by DRI drivers and
109<code>egl_dri2</code> EGL driver.
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]110
111</li>
Chia-I Wua1306f42010-01-22 15:51:51 +0800[diff] [blame]112
113<li><code>--enable-gallium-swrast</code>
114
115<p>This option is not specific to EGL. But if there is no driver for your
116hardware, or you are experiencing problems with the hardware driver, you can
117enable the swrast DRM driver. It is a dummy driver and EGL will fallback to
118software rendering automatically.</p>
119
120</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]121</ul>
122
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]123<h2>Use EGL</h2>
124
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]125<h3>Demos</h3>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]126
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]127<p>There are demos for the client APIs supported by EGL. They can be found in
128mesa/demos repository.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]129
130<h3>Environment Variables</h3>
131
132<p>There are several environment variables that control the behavior of EGL at
133runtime</p>
134
135<ul>
Chia-I Wu5d8646c2010-02-02 15:34:55 +0800[diff] [blame]136<li><code>EGL_DRIVERS_PATH</code>
137
138<p>By default, the main library will look for drivers in the directory where
139the drivers are installed to. This variable specifies a list of
140colon-separated directories where the main library will look for drivers, in
Chia-I Wu6fd8b6a2010-02-02 16:47:53 +0800[diff] [blame]141addition to the default directory. This variable is ignored for setuid/setgid
142binaries.</p>
Chia-I Wu5d8646c2010-02-02 15:34:55 +0800[diff] [blame]143
144</li>
145
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]146<li><code>EGL_DRIVER</code>
147
Chia-I Wu7fc35812010-02-02 11:05:19 +0800[diff] [blame]148<p>This variable specifies a full path to an EGL driver and it forces the
149specified EGL driver to be loaded. It comes in handy when one wants to test a
Chia-I Wu6fd8b6a2010-02-02 16:47:53 +0800[diff] [blame]150specific driver. This variable is ignored for setuid/setgid binaries.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]151
152</li>
153
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]154<li><code>EGL_PLATFORM</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]155
156<p>When <code>EGL_DRIVER</code> is not set, the main library loads <em>all</em>
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]157EGL drivers that support a certain window system. <code>EGL_PLATFORM</code>
158can be used to specify the window system and the valid values are, for example,
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]159<code>x11</code> or <code>kms</code>. When the variable is not set, the main
160library defaults the value to the first window system listed in
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]161<code>--with-egl-platforms</code> at configuration time.
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]162
163</li>
164
165<li><code>EGL_LOG_LEVEL</code>
166
167<p>This changes the log level of the main library and the drivers. The valid
168values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
169<code>fatal</code>.</p>
170
171</li>
172
173<li><code>EGL_SOFTWARE</code>
174
175<p>For drivers that support both hardware and software rendering, setting this
176variable to true forces the use of software rendering.</p>
177
178</li>
179</ul>
180
181<h2>EGL Drivers</h2>
182
183<p>There are two categories of EGL drivers: Gallium and classic.</p>
184
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]185<p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4. These
186drivers depend on the <code>egl</code> state tracker to build. The available
187drivers are</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]188
189<ul>
190<li><code>egl_&lt;dpy&gt;_i915</code></li>
191<li><code>egl_&lt;dpy&gt;_i965</code></li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]192<li><code>egl_&lt;dpy&gt;_nouveau</code></li>
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]193<li><code>egl_&lt;dpy&gt;_radeon</code></li>
Chia-I Wua1306f42010-01-22 15:51:51 +0800[diff] [blame]194<li><code>egl_&lt;dpy&gt;_swrast</code></li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]195<li><code>egl_&lt;dpy&gt;_vmwgfx</code></li>
196</ul>
197
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]198<p><code>&lt;dpy&gt;</code> is given by <code>--with-egl-platforms</code> at
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]199configuration time. There is usually one EGL driver for each combination of
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]200the platforms listed and the pipe drivers enabled. When the platform is pure
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]201software or pure hardware, non-working combinations will not be built.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]202
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]203<p>Classic EGL drivers, on the other hand, support only a subset of the
204available rendering APIs. They can be found under
205<code>src/egl/drivers/</code>. There are 3 of them</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]206
207<ul>
208<li><code>egl_glx</code>
209
210<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
211the EGL API. It supports both direct and indirect rendering when the GLX does.
212It is accelerated when the GLX is. As such, it cannot provide functions that
213is not available in GLX or GLX extensions.</p>
214</li>
215
Chia-I Wu5f08eff2010-02-05 11:46:28 +0800[diff] [blame]216<li><code>egl_dri2</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]217
218<p>This driver supports the X Window System as its window system. It functions
Chia-I Wu5f08eff2010-02-05 11:46:28 +0800[diff] [blame]219as a DRI2 driver loader. Unlike <code>egl_glx</code>, it has no dependency on
220<code>libGL</code>. It talks to the X server directly using DRI2 protocol.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]221
222</li>
223<li><code>egl_dri</code>
224
225<p>This driver lacks maintenance and does <em>not</em> build. It is similiar
Chia-I Wu5f08eff2010-02-05 11:46:28 +0800[diff] [blame]226to <code>egl_dri2</code> in that it functions as a DRI(1) driver loader. But
227unlike <code>egl_dri2</code>, it supports Linux framebuffer devices as its
228window system and supports EGL_MESA_screen_surface extension. As DRI1 drivers
229are phasing out, it might eventually be replaced by <code>egl_dri2</code>.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]230
231</li>
232</ul>
233
234<p>To use the classic drivers, one must manually set <code>EGL_DRIVER</code> at
235runtime.</p>
236
237<h2>Developers</h2>
238
Chia-I Wu14cbf322010-01-27 23:18:22 +0800[diff] [blame]239<p>The sources of the main library and the classic drivers can be found at
Chia-I Wu3c967a92010-01-22 16:31:43 +0800[diff] [blame]240<code>src/egl/</code>. The sources of the <code>egl</code> state tracker can
Chia-I Wu14cbf322010-01-27 23:18:22 +0800[diff] [blame]241be found at <code>src/gallium/state_trackers/egl/</code>.</p>
242
243<p>The suggested way to learn to write a EGL driver is to see how other drivers
244are written. <code>egl_glx</code> should be a good reference. It works in any
245environment that has GLX support, and it is simpler than most drivers.</p>
246
247<h3>Lifetime of Display Resources</h3>
248
249<p>Contexts and surfaces are examples of display resources. They might live
250longer than the display that creates them.</p>
251
252<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
253display resources should be destroyed. Similarly, when a thread is released
254throught <code>eglReleaseThread</code>, all current display resources should be
255released. Another way to destory or release resources is through functions
256such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
257
258<p>When a resource that is current to some thread is destroyed, the resource
259should not be destroyed immediately. EGL requires the resource to live until
260it is no longer current. A driver usually calls
261<code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
262(current) to any thread in the destroy callbacks. If it is still bound, the
263resource is not destroyed.</p>
264
265<p>The main library will mark destroyed current resources as unlinked. In a
266driver's <code>MakeCurrent</code> callback,
267<code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
268released resource is linked to a display. If it is not, the last reference to
269the resource is removed and the driver should destroy the resource. But it
270should be careful here because <code>MakeCurrent</code> might be called with an
271uninitialized display.</p>
272
273<p>This is the only mechanism provided by the main library to help manage the
274resources. The drivers are responsible to the correct behavior as defined by
275EGL.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]276
Chia-I Wu1b2b08c2010-02-05 12:44:45 +0800[diff] [blame]277<h3><code>EGL_RENDER_BUFFER</code></h3>
278
279<p>In EGL, the color buffer a context should try to render to is decided by the
280binding surface. It should try to render to the front buffer if the binding
281surface has <code>EGL_RENDER_BUFFER</code> set to
282<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
283surface with <code>EGL_RENDER_BUFFER</code> set to
284<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
285buffer. However, the context is allowed to make the final decision as to which
286color buffer it wants to or is able to render to.</p>
287
288<p>For pbuffer surfaces, the render buffer is always
289<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
290always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
291requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
292result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
293<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
294config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
295pbuffer surfaces.</p>
296
297<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
298single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
299is desirable that a driver allocates a private color buffer for each pbuffer
300surface created. If the window system the driver supports has native pbuffers,
301or if the native pixmaps have more than one color buffers, the driver should
302carefully attach the native color buffers to the EGL surfaces, re-route them if
303required.</p>
304
305<p>There is no defined behavior as to, for example, how
306<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
307now, it is desired that the draw buffer in a client API be fixed for pixmap and
308pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
309client API renders to the specified render buffer for pixmap and pbuffer
310surfaces.</p>
311
Chia-I Wue16f5772010-02-17 19:52:29 +0800[diff] [blame]312<h3><code>EGLDisplay</code> Mutex</h3>
313
314The <code>EGLDisplay</code> will be locked before calling any of the dispatch
315functions (well, except for GetProcAddress which does not take an
316<code>EGLDisplay</code>). This guarantees that the same dispatch function will
317not be called with the sample display at the same time. If a driver has access
318to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
319should as well lock the display before using it.
320
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]321<h3>TODOs</h3>
322
323<ul>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]324<li>Pass the conformance tests</li>
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]325<li>Better automatic driver selection: <code>EGL_PLATFORM</code> loads all
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]326drivers and might eat too much memory.</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]327
328</ul>
329
330</body>
331</html>