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Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]1<html>
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3<title>Mesa EGL</title>
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5<head><link rel="stylesheet" type="text/css" href="mesa.css"></head>
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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>
129<li><code>EGL_DRIVER</code>
130
Chia-I Wu7fc35812010-02-02 11:05:19 +0800[diff] [blame]131<p>This variable specifies a full path to an EGL driver and it forces the
132specified EGL driver to be loaded. It comes in handy when one wants to test a
133specific driver.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]134
135</li>
136
137<li><code>EGL_DISPLAY</code>
138
139<p>When <code>EGL_DRIVER</code> is not set, the main library loads <em>all</em>
140EGL drivers that support a certain window system. <code>EGL_DISPLAY</code> can
141be used to specify the window system and the valid values are, for example,
142<code>x11</code> or <code>kms</code>. When the variable is not set, the main
143library defaults the value to the first window system listed in
144<code>--with-egl-displays</code> at configuration time.
145
146</li>
147
148<li><code>EGL_LOG_LEVEL</code>
149
150<p>This changes the log level of the main library and the drivers. The valid
151values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
152<code>fatal</code>.</p>
153
154</li>
155
156<li><code>EGL_SOFTWARE</code>
157
158<p>For drivers that support both hardware and software rendering, setting this
159variable to true forces the use of software rendering.</p>
160
161</li>
162</ul>
163
164<h2>EGL Drivers</h2>
165
166<p>There are two categories of EGL drivers: Gallium and classic.</p>
167
168<p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4. The
169support for optional EGL functions and EGL extensions is usually more complete
Chia-I Wu3c967a92010-01-22 16:31:43 +0800[diff] [blame]170than the classic ones. These drivers depend on the <code>egl</code> state
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]171tracker to build. The available drivers are</p>
172
173<ul>
174<li><code>egl_&lt;dpy&gt;_i915</code></li>
175<li><code>egl_&lt;dpy&gt;_i965</code></li>
176<li><code>egl_&lt;dpy&gt;_radeon</code></li>
177<li><code>egl_&lt;dpy&gt;_nouveau</code></li>
Chia-I Wua1306f42010-01-22 15:51:51 +0800[diff] [blame]178<li><code>egl_&lt;dpy&gt;_swrast</code></li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]179<li><code>egl_&lt;dpy&gt;_vmwgfx</code></li>
180</ul>
181
182<p><code>&lt;dpy&gt;</code> is given by <code>--with-egl-displays</code> at
183configuration time. There will be one EGL driver for each combination of the
184displays listed and the hardware drivers enabled.</p>
185
186<p>Classic EGL drivers, on the other hand, supports only OpenGL as its
187rendering API. They can be found under <code>src/egl/drivers/</code>. There
188are 3 of them</p>
189
190<ul>
191<li><code>egl_glx</code>
192
193<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
194the EGL API. It supports both direct and indirect rendering when the GLX does.
195It is accelerated when the GLX is. As such, it cannot provide functions that
196is not available in GLX or GLX extensions.</p>
197</li>
198
199<li><code>egl_xdri</code>
200
201<p>This driver supports the X Window System as its window system. It functions
Chia-I Wu29732f92010-01-22 15:05:31 +0800[diff] [blame]202as a DRI driver loader and can load DRI/DRI2/DRISW drivers. Unlike
203<code>egl_glx</code>, it has no dependency on <code>libGL</code>. It talks to
204the X server directly using DRI or DRI2 protocols. It also talks minimal GLX
205protocol for things like available visuals or fbconfigs. With direct access to
206the DRI drivers, it has the potential to support more EGL functions that are
207not possible with <code>egl_glx</code>.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]208
209</li>
210<li><code>egl_dri</code>
211
212<p>This driver lacks maintenance and does <em>not</em> build. It is similiar
213to <code>egl_xdri</code> in that it functions as a DRI driver loader. But
214unlike <code>egl_xdri</code>, it supports Linux framebuffer devices as its
215window system and supports EGL_MESA_screen_surface extension. It loads only
216DRI1 drivers. As DRI1 drivers is phasing out, it might be better to rewrite
217the driver to support KMS and DRI2.</p>
218
219</li>
220</ul>
221
222<p>To use the classic drivers, one must manually set <code>EGL_DRIVER</code> at
223runtime.</p>
224
225<h2>Developers</h2>
226
Chia-I Wu14cbf322010-01-27 23:18:22 +0800[diff] [blame]227<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]228<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]229be found at <code>src/gallium/state_trackers/egl/</code>.</p>
230
231<p>The suggested way to learn to write a EGL driver is to see how other drivers
232are written. <code>egl_glx</code> should be a good reference. It works in any
233environment that has GLX support, and it is simpler than most drivers.</p>
234
235<h3>Lifetime of Display Resources</h3>
236
237<p>Contexts and surfaces are examples of display resources. They might live
238longer than the display that creates them.</p>
239
240<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
241display resources should be destroyed. Similarly, when a thread is released
242throught <code>eglReleaseThread</code>, all current display resources should be
243released. Another way to destory or release resources is through functions
244such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
245
246<p>When a resource that is current to some thread is destroyed, the resource
247should not be destroyed immediately. EGL requires the resource to live until
248it is no longer current. A driver usually calls
249<code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
250(current) to any thread in the destroy callbacks. If it is still bound, the
251resource is not destroyed.</p>
252
253<p>The main library will mark destroyed current resources as unlinked. In a
254driver's <code>MakeCurrent</code> callback,
255<code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
256released resource is linked to a display. If it is not, the last reference to
257the resource is removed and the driver should destroy the resource. But it
258should be careful here because <code>MakeCurrent</code> might be called with an
259uninitialized display.</p>
260
261<p>This is the only mechanism provided by the main library to help manage the
262resources. The drivers are responsible to the correct behavior as defined by
263EGL.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]264
265<h3>TODOs</h3>
266
267<ul>
268<li>Thread safety</li>
269<li>Pass the conformance tests</li>
270<li>Better automatic driver selection: <code>EGL_DISPLAY</code> loads all
271drivers and might eat too much memory.</li>
Chia-I Wua6342af2010-01-26 10:54:45 +0800[diff] [blame]272<li>Stop using <code>glxinit.c</code> and sources from <code>src/glx/x11/</code></li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]273
274</ul>
275
276</body>
277</html>