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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>
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]31<p>Run <code>configure</code> with the desired client APIs and enable
32the driver for your hardware. For example</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]33
34<pre>
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]35 $ ./configure --enable-gles2 --enable-openvg --enable-gallium-nouveau
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]36</pre>
37
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]38<p>The main library and OpenGL is enabled by default. The first option above
39enables <a href="opengles.html">OpenGL ES 2.x</a>. The second option enables
40<a href="openvg.html">OpenVG</a>.</p>
Chia-I Wuc6320c52010-10-28 17:25:07 +0800[diff] [blame]41
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]42</li>
43
44<li>Build and install Mesa as usual.</li>
45</ol>
46
47<p>In the given example, it will build and install <code>libEGL</code>,
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]48<code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>,
49<code>libOpenVG</code>, and one or more EGL drivers.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]50
51<h3>Configure Options</h3>
52
53<p>There are several options that control the build of EGL at configuration
54time</p>
55
56<ul>
57<li><code>--enable-egl</code>
58
59<p>By default, EGL is enabled. When disabled, the main library and the drivers
60will not be built.</p>
61
62</li>
63
Chia-I Wua6342af2010-01-26 10:54:45 +0800[diff] [blame]64<li><code>--with-egl-driver-dir</code>
65
66<p>The directory EGL drivers should be installed to. If not specified, EGL
67drivers will be installed to <code>${libdir}/egl</code>.</p>
68
69</li>
70
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]71<li><code>--with-egl-platforms</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]72
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]73<p>List the platforms (window systems) to support. Its argument is a comma
Chia-I Wue7424d72010-09-19 16:54:39 +0800[diff] [blame]74seprated string such as <code>--with-egl-platforms=x11,drm</code>. It decides
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]75the platforms a driver may support. The first listed platform is also used by
76the main library to decide the native platform: the platform the EGL native
77types such as <code>EGLNativeDisplayType</code> or
78<code>EGLNativeWindowType</code> defined for.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]79
Chia-I Wue7424d72010-09-19 16:54:39 +0800[diff] [blame]80<p>The available platforms are <code>x11</code>, <code>drm</code>,
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]81<code>fbdev</code>, and <code>gdi</code>. The <code>gdi</code> platform can
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]82only be built with SCons. Unless for special needs, the build system should
83select the right platforms automatically.</p>
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]84
85</li>
86
87<li><code>--enable-gles1</code> and <code>--enable-gles2</code>
88
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]89<p>These options enable OpenGL ES support in OpenGL. The result is
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]90one big library that supports multiple APIs.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]91
92</li>
Chia-I Wua1306f42010-01-22 15:51:51 +0800[diff] [blame]93
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]94<li><code>--enable-gles-overlay</code>
95
96<p>This option enables OpenGL ES as separate libraries. This is an alternative
97approach to enable OpenGL ES. It is only supported by
98<code>egl_gallium</code>.</p>
99
100</li>
101
Chia-I Wuc6320c52010-10-28 17:25:07 +0800[diff] [blame]102<li><code>--enable-openvg</code>
103
104<p>OpenVG must be explicitly enabled by this option.</p>
105
106</li>
107
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]108<li><code>--enable-gallium-egl</code>
109
110<p>Explicitly enable or disable <code>egl_gallium</code>.</p>
111
112</li>
113
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]114</ul>
115
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]116<h2>Use EGL</h2>
117
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]118<h3>Demos</h3>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]119
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]120<p>There are demos for the client APIs supported by EGL. They can be found in
121mesa/demos repository.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]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
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]147<li><code>EGL_PLATFORM</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]148
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]149<p>This variable specifies the native platform. The valid values are the same
150as those for <code>--with-egl-platforms</code>. When the variable is not set,
151the main library uses the first platform listed in
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]152<code>--with-egl-platforms</code> as the native platform.</p>
153
154<p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
155create displays for non-native platforms. These extensions are usually used by
156applications that support non-native platforms. Setting this variable is
157probably required only for some of the demos found in mesa/demo repository.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]158
159</li>
160
161<li><code>EGL_LOG_LEVEL</code>
162
163<p>This changes the log level of the main library and the drivers. The valid
164values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
165<code>fatal</code>.</p>
166
167</li>
168
169<li><code>EGL_SOFTWARE</code>
170
171<p>For drivers that support both hardware and software rendering, setting this
172variable to true forces the use of software rendering.</p>
173
174</li>
175</ul>
176
177<h2>EGL Drivers</h2>
178
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]179<ul>
Chia-I Wu3418f742010-11-02 23:55:56 +0800[diff] [blame]180<li><code>egl_dri2</code>
181
182<p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
183It functions as a DRI2 driver loader. For <code>x11</code> support, it talks
184to the X server directly using (XCB-)DRI2 protocol.</p>
185
186</li>
187
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]188<li><code>egl_gallium</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]189
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]190<p>This driver is based on Gallium3D. It supports all rendering APIs and
191hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
Chia-I Wuc6320c52010-10-28 17:25:07 +0800[diff] [blame]192The supported platforms are X11, DRM, FBDEV, and GDI.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]193
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]194</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]195
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]196<li><code>egl_glx</code>
197
198<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
199the EGL API. It supports both direct and indirect rendering when the GLX does.
200It is accelerated when the GLX is. As such, it cannot provide functions that
201is not available in GLX or GLX extensions.</p>
202</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]203</ul>
204
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]205<h2>Developers</h2>
206
Chia-I Wu14cbf322010-01-27 23:18:22 +0800[diff] [blame]207<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]208<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]209be found at <code>src/gallium/state_trackers/egl/</code>.</p>
210
211<p>The suggested way to learn to write a EGL driver is to see how other drivers
212are written. <code>egl_glx</code> should be a good reference. It works in any
213environment that has GLX support, and it is simpler than most drivers.</p>
214
215<h3>Lifetime of Display Resources</h3>
216
217<p>Contexts and surfaces are examples of display resources. They might live
218longer than the display that creates them.</p>
219
220<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
221display resources should be destroyed. Similarly, when a thread is released
222throught <code>eglReleaseThread</code>, all current display resources should be
223released. Another way to destory or release resources is through functions
224such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
225
226<p>When a resource that is current to some thread is destroyed, the resource
227should not be destroyed immediately. EGL requires the resource to live until
228it is no longer current. A driver usually calls
229<code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
230(current) to any thread in the destroy callbacks. If it is still bound, the
231resource is not destroyed.</p>
232
233<p>The main library will mark destroyed current resources as unlinked. In a
234driver's <code>MakeCurrent</code> callback,
235<code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
236released resource is linked to a display. If it is not, the last reference to
237the resource is removed and the driver should destroy the resource. But it
238should be careful here because <code>MakeCurrent</code> might be called with an
239uninitialized display.</p>
240
241<p>This is the only mechanism provided by the main library to help manage the
242resources. The drivers are responsible to the correct behavior as defined by
243EGL.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]244
Chia-I Wu1b2b08c2010-02-05 12:44:45 +0800[diff] [blame]245<h3><code>EGL_RENDER_BUFFER</code></h3>
246
247<p>In EGL, the color buffer a context should try to render to is decided by the
248binding surface. It should try to render to the front buffer if the binding
249surface has <code>EGL_RENDER_BUFFER</code> set to
250<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
251surface with <code>EGL_RENDER_BUFFER</code> set to
252<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
253buffer. However, the context is allowed to make the final decision as to which
254color buffer it wants to or is able to render to.</p>
255
256<p>For pbuffer surfaces, the render buffer is always
257<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
258always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
259requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
260result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
261<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
262config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
263pbuffer surfaces.</p>
264
265<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
266single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
267is desirable that a driver allocates a private color buffer for each pbuffer
268surface created. If the window system the driver supports has native pbuffers,
269or if the native pixmaps have more than one color buffers, the driver should
270carefully attach the native color buffers to the EGL surfaces, re-route them if
271required.</p>
272
273<p>There is no defined behavior as to, for example, how
274<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
275now, it is desired that the draw buffer in a client API be fixed for pixmap and
276pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
277client API renders to the specified render buffer for pixmap and pbuffer
278surfaces.</p>
279
Chia-I Wue16f5772010-02-17 19:52:29 +0800[diff] [blame]280<h3><code>EGLDisplay</code> Mutex</h3>
281
282The <code>EGLDisplay</code> will be locked before calling any of the dispatch
283functions (well, except for GetProcAddress which does not take an
284<code>EGLDisplay</code>). This guarantees that the same dispatch function will
285not be called with the sample display at the same time. If a driver has access
286to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
287should as well lock the display before using it.
288
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]289<h3>TODOs</h3>
290
291<ul>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]292<li>Pass the conformance tests</li>
Chia-I Wu68071822010-09-09 13:51:59 +0800[diff] [blame]293<li>Mixed use of OpenGL, OpenGL ES 1.1, and OpenGL ES 2.0 is supported. But
294which one of <code>libGL.so</code>, <code>libGLESv1_CM.so</code>, and
295<code>libGLESv2.so</code> should an application link to? Bad things may happen
296when, say, an application is linked to <code>libGLESv2.so</code> and
297<code>libcairo</code>, which is linked to <code>libGL.so</code> instead.</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]298
299</ul>
300
301</body>
302</html>