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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>
31<p>Run <code>configure</code> with the desired state trackers and and enable
32the Gallium driver for your hardware. For example</p>
33
34<pre>
Chia-I Wua6342af2010-01-26 10:54:45 +0800[diff] [blame]35 $ ./configure --with-state-trackers=egl,es,vega --enable-gallium-{swrast,intel}
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]36</pre>
37
Chia-I Wu3c967a92010-01-22 16:31:43 +0800[diff] [blame]38<p>The main library will be enabled by default. The <code>egl</code> state
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]39tracker is needed by a number of EGL drivers. EGL drivers will be covered
40later. The <a href="opengles.html">es state tracker</a> provides OpenGL ES 1.x
41and 2.x and the <a href="openvg.html">vega state tracker</a> provides OpenVG
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>,
49<code>libGLESv1_CM</code>, <code>libGLESv2</code>, <code>libOpenVG</code>, and
50one or more EGL drivers.</p>
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 Wuada46052010-01-21 15:29:14 +0800[diff] [blame]72<li><code>--with-egl-displays</code>
73
74<p>List the window system(s) to support. It is by default <code>x11</code>,
75which supports the X Window System. Its argument is a comma separated string
76like, for example, <code>--with-egl-displays=x11,kms</code>. Because an EGL
77driver decides which window system to support, this example will enable two
78(sets of) EGL drivers. One supports the X window system and the other supports
79bare KMS (kernel modesetting).</p>
80
81</li>
82
83<li><code>--with-state-trackers</code>
84
85<p>The argument is a comma separated string. It is usually used to specify the
86rendering APIs, like OpenGL ES or OpenVG, to build. But it should be noted
Chia-I Wu3c967a92010-01-22 16:31:43 +0800[diff] [blame]87that a number of EGL drivers depend on the <code>egl</code> state tracker.
88They will <em>not</em> be built without the <code>egl</code> state tracker.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]89
90</li>
Chia-I Wua1306f42010-01-22 15:51:51 +0800[diff] [blame]91
92<li><code>--enable-gallium-swrast</code>
93
94<p>This option is not specific to EGL. But if there is no driver for your
95hardware, or you are experiencing problems with the hardware driver, you can
96enable the swrast DRM driver. It is a dummy driver and EGL will fallback to
97software rendering automatically.</p>
98
99</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]100</ul>
101
102<h3>OpenGL</h3>
103
104<p>The OpenGL state tracker is not built in the above example. It should be
105noted that the classic <code>libGL</code> is not a state tracker and cannot be
106used with EGL (unless the EGL driver in use is <code>egl_glx</code>). To build
107the OpenGL state tracker, one may append <code>glx</code> to
108<code>--with-state-trackers</code> and manually build
109<code>src/gallium/winsys/xlib/</code>.</p>
110
111<h2>Use EGL</h2>
112
113<p> The demos for OpenGL ES and OpenVG can be found in <code>progs/es1/</code>,
114<code>progs/es2/</code> and <code>progs/openvg/</code>. You can use them to
115test your build. For example,</p>
116
117<pre>
118 $ cd progs/es1/xegl
119 $ make
120 $ ./torus
121</pre>
122
123<h3>Environment Variables</h3>
124
125<p>There are several environment variables that control the behavior of EGL at
126runtime</p>
127
128<ul>
Chia-I Wu5d8646c2010-02-02 15:34:55 +0800[diff] [blame]129<li><code>EGL_DRIVERS_PATH</code>
130
131<p>By default, the main library will look for drivers in the directory where
132the drivers are installed to. This variable specifies a list of
133colon-separated directories where the main library will look for drivers, in
Chia-I Wu6fd8b6a2010-02-02 16:47:53 +0800[diff] [blame]134addition to the default directory. This variable is ignored for setuid/setgid
135binaries.</p>
Chia-I Wu5d8646c2010-02-02 15:34:55 +0800[diff] [blame]136
137</li>
138
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]139<li><code>EGL_DRIVER</code>
140
Chia-I Wu7fc35812010-02-02 11:05:19 +0800[diff] [blame]141<p>This variable specifies a full path to an EGL driver and it forces the
142specified 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]143specific driver. This variable is ignored for setuid/setgid binaries.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]144
145</li>
146
147<li><code>EGL_DISPLAY</code>
148
149<p>When <code>EGL_DRIVER</code> is not set, the main library loads <em>all</em>
150EGL drivers that support a certain window system. <code>EGL_DISPLAY</code> can
151be used to specify the window system and the valid values are, for example,
152<code>x11</code> or <code>kms</code>. When the variable is not set, the main
153library defaults the value to the first window system listed in
154<code>--with-egl-displays</code> at configuration time.
155
156</li>
157
158<li><code>EGL_LOG_LEVEL</code>
159
160<p>This changes the log level of the main library and the drivers. The valid
161values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
162<code>fatal</code>.</p>
163
164</li>
165
166<li><code>EGL_SOFTWARE</code>
167
168<p>For drivers that support both hardware and software rendering, setting this
169variable to true forces the use of software rendering.</p>
170
171</li>
172</ul>
173
174<h2>EGL Drivers</h2>
175
176<p>There are two categories of EGL drivers: Gallium and classic.</p>
177
178<p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4. The
179support for optional EGL functions and EGL extensions is usually more complete
Chia-I Wu3c967a92010-01-22 16:31:43 +0800[diff] [blame]180than the classic ones. These drivers depend on the <code>egl</code> state
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]181tracker to build. The available drivers are</p>
182
183<ul>
184<li><code>egl_&lt;dpy&gt;_i915</code></li>
185<li><code>egl_&lt;dpy&gt;_i965</code></li>
186<li><code>egl_&lt;dpy&gt;_radeon</code></li>
187<li><code>egl_&lt;dpy&gt;_nouveau</code></li>
Chia-I Wua1306f42010-01-22 15:51:51 +0800[diff] [blame]188<li><code>egl_&lt;dpy&gt;_swrast</code></li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]189<li><code>egl_&lt;dpy&gt;_vmwgfx</code></li>
190</ul>
191
192<p><code>&lt;dpy&gt;</code> is given by <code>--with-egl-displays</code> at
193configuration time. There will be one EGL driver for each combination of the
194displays listed and the hardware drivers enabled.</p>
195
196<p>Classic EGL drivers, on the other hand, supports only OpenGL as its
197rendering API. They can be found under <code>src/egl/drivers/</code>. There
198are 3 of them</p>
199
200<ul>
201<li><code>egl_glx</code>
202
203<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
204the EGL API. It supports both direct and indirect rendering when the GLX does.
205It is accelerated when the GLX is. As such, it cannot provide functions that
206is not available in GLX or GLX extensions.</p>
207</li>
208
Chia-I Wu5f08eff2010-02-05 11:46:28 +0800[diff] [blame]209<li><code>egl_dri2</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]210
211<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]212as a DRI2 driver loader. Unlike <code>egl_glx</code>, it has no dependency on
213<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]214
215</li>
216<li><code>egl_dri</code>
217
218<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]219to <code>egl_dri2</code> in that it functions as a DRI(1) driver loader. But
220unlike <code>egl_dri2</code>, it supports Linux framebuffer devices as its
221window system and supports EGL_MESA_screen_surface extension. As DRI1 drivers
222are phasing out, it might eventually be replaced by <code>egl_dri2</code>.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]223
224</li>
225</ul>
226
227<p>To use the classic drivers, one must manually set <code>EGL_DRIVER</code> at
228runtime.</p>
229
230<h2>Developers</h2>
231
Chia-I Wu14cbf322010-01-27 23:18:22 +0800[diff] [blame]232<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]233<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]234be found at <code>src/gallium/state_trackers/egl/</code>.</p>
235
236<p>The suggested way to learn to write a EGL driver is to see how other drivers
237are written. <code>egl_glx</code> should be a good reference. It works in any
238environment that has GLX support, and it is simpler than most drivers.</p>
239
240<h3>Lifetime of Display Resources</h3>
241
242<p>Contexts and surfaces are examples of display resources. They might live
243longer than the display that creates them.</p>
244
245<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
246display resources should be destroyed. Similarly, when a thread is released
247throught <code>eglReleaseThread</code>, all current display resources should be
248released. Another way to destory or release resources is through functions
249such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
250
251<p>When a resource that is current to some thread is destroyed, the resource
252should not be destroyed immediately. EGL requires the resource to live until
253it is no longer current. A driver usually calls
254<code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
255(current) to any thread in the destroy callbacks. If it is still bound, the
256resource is not destroyed.</p>
257
258<p>The main library will mark destroyed current resources as unlinked. In a
259driver's <code>MakeCurrent</code> callback,
260<code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
261released resource is linked to a display. If it is not, the last reference to
262the resource is removed and the driver should destroy the resource. But it
263should be careful here because <code>MakeCurrent</code> might be called with an
264uninitialized display.</p>
265
266<p>This is the only mechanism provided by the main library to help manage the
267resources. The drivers are responsible to the correct behavior as defined by
268EGL.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]269
Chia-I Wu1b2b08c2010-02-05 12:44:45 +0800[diff] [blame]270<h3><code>EGL_RENDER_BUFFER</code></h3>
271
272<p>In EGL, the color buffer a context should try to render to is decided by the
273binding surface. It should try to render to the front buffer if the binding
274surface has <code>EGL_RENDER_BUFFER</code> set to
275<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
276surface with <code>EGL_RENDER_BUFFER</code> set to
277<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
278buffer. However, the context is allowed to make the final decision as to which
279color buffer it wants to or is able to render to.</p>
280
281<p>For pbuffer surfaces, the render buffer is always
282<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
283always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
284requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
285result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
286<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
287config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
288pbuffer surfaces.</p>
289
290<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
291single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
292is desirable that a driver allocates a private color buffer for each pbuffer
293surface created. If the window system the driver supports has native pbuffers,
294or if the native pixmaps have more than one color buffers, the driver should
295carefully attach the native color buffers to the EGL surfaces, re-route them if
296required.</p>
297
298<p>There is no defined behavior as to, for example, how
299<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
300now, it is desired that the draw buffer in a client API be fixed for pixmap and
301pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
302client API renders to the specified render buffer for pixmap and pbuffer
303surfaces.</p>
304
Chia-I Wue16f5772010-02-17 19:52:29 +0800[diff] [blame^]305<h3><code>EGLDisplay</code> Mutex</h3>
306
307The <code>EGLDisplay</code> will be locked before calling any of the dispatch
308functions (well, except for GetProcAddress which does not take an
309<code>EGLDisplay</code>). This guarantees that the same dispatch function will
310not be called with the sample display at the same time. If a driver has access
311to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
312should as well lock the display before using it.
313
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]314<h3>TODOs</h3>
315
316<ul>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]317<li>Pass the conformance tests</li>
318<li>Better automatic driver selection: <code>EGL_DISPLAY</code> loads all
319drivers and might eat too much memory.</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]320
321</ul>
322
323</body>
324</html>