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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 Wuc6320c52010-10-28 17:25:07 +0800[diff] [blame]35 $ ./configure --enable-gles-overlay --enable-openvg --enable-gallium-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
Chia-I Wuc6320c52010-10-28 17:25:07 +0800[diff] [blame]39<a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The second option enables
40<a href="openvg.html">OpenVG</a>.
41</p>
42
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]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 Wub365b152010-07-03 17:18:40 +0800[diff] [blame]74<p>List the platforms (window systems) to support. Its argument is a comma
Chia-I Wue7424d72010-09-19 16:54:39 +0800[diff] [blame]75seprated string such as <code>--with-egl-platforms=x11,drm</code>. It decides
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]76the platforms a driver may support. The first listed platform is also used by
77the main library to decide the native platform: the platform the EGL native
78types such as <code>EGLNativeDisplayType</code> or
79<code>EGLNativeWindowType</code> defined for.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]80
Chia-I Wue7424d72010-09-19 16:54:39 +0800[diff] [blame]81<p>The available platforms are <code>x11</code>, <code>drm</code>,
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]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
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]87<li><code>--enable-gles-overlay</code>
88
Chia-I Wuc6320c52010-10-28 17:25:07 +0800[diff] [blame]89<p>OpenGL is built by default. To build OpenGL ES, this option must be
90explicitly given.</p>
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]91
92</li>
93
94<li><code>--enable-gles1</code> and <code>--enable-gles2</code>
95
96<p>Unlike <code>--enable-gles-overlay</code>, which builds one library for each
97rendering API, these options enable OpenGL ES support in OpenGL. The result is
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]98one big library that supports multiple APIs.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]99
100</li>
Chia-I Wua1306f42010-01-22 15:51:51 +0800[diff] [blame]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 Wuada46052010-01-21 15:29:14 +0800[diff] [blame]108</ul>
109
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]110<h2>Use EGL</h2>
111
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]112<h3>Demos</h3>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]113
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]114<p>There are demos for the client APIs supported by EGL. They can be found in
115mesa/demos repository.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]116
117<h3>Environment Variables</h3>
118
119<p>There are several environment variables that control the behavior of EGL at
120runtime</p>
121
122<ul>
Chia-I Wu5d8646c2010-02-02 15:34:55 +0800[diff] [blame]123<li><code>EGL_DRIVERS_PATH</code>
124
125<p>By default, the main library will look for drivers in the directory where
126the drivers are installed to. This variable specifies a list of
127colon-separated directories where the main library will look for drivers, in
Chia-I Wu6fd8b6a2010-02-02 16:47:53 +0800[diff] [blame]128addition to the default directory. This variable is ignored for setuid/setgid
129binaries.</p>
Chia-I Wu5d8646c2010-02-02 15:34:55 +0800[diff] [blame]130
131</li>
132
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]133<li><code>EGL_DRIVER</code>
134
Chia-I Wu7fc35812010-02-02 11:05:19 +0800[diff] [blame]135<p>This variable specifies a full path to an EGL driver and it forces the
136specified 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]137specific driver. This variable is ignored for setuid/setgid binaries.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]138
139</li>
140
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]141<li><code>EGL_PLATFORM</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]142
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]143<p>This variable specifies the native platform. The valid values are the same
144as those for <code>--with-egl-platforms</code>. When the variable is not set,
145the main library uses the first platform listed in
146<code>--with-egl-platforms</code> as the native platform</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]147
148</li>
149
150<li><code>EGL_LOG_LEVEL</code>
151
152<p>This changes the log level of the main library and the drivers. The valid
153values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
154<code>fatal</code>.</p>
155
156</li>
157
158<li><code>EGL_SOFTWARE</code>
159
160<p>For drivers that support both hardware and software rendering, setting this
161variable to true forces the use of software rendering.</p>
162
163</li>
164</ul>
165
166<h2>EGL Drivers</h2>
167
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]168<ul>
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]169<li><code>egl_gallium</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]170
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]171<p>This driver is based on Gallium3D. It supports all rendering APIs and
172hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
Chia-I Wuc6320c52010-10-28 17:25:07 +0800[diff] [blame]173The supported platforms are X11, DRM, FBDEV, and GDI.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]174
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]175</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]176
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]177<li><code>egl_glx</code>
178
179<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
180the EGL API. It supports both direct and indirect rendering when the GLX does.
181It is accelerated when the GLX is. As such, it cannot provide functions that
182is not available in GLX or GLX extensions.</p>
183</li>
184
Chia-I Wu5f08eff2010-02-05 11:46:28 +0800[diff] [blame]185<li><code>egl_dri2</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]186
187<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]188as a DRI2 driver loader. Unlike <code>egl_glx</code>, it has no dependency on
Chia-I Wuc6320c52010-10-28 17:25:07 +0800[diff] [blame]189<code>libGL</code>. It talks to the X server directly using (XCB-)DRI2
190protocol.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]191
192</li>
193</ul>
194
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]195<h2>Developers</h2>
196
Chia-I Wu14cbf322010-01-27 23:18:22 +0800[diff] [blame]197<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]198<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]199be found at <code>src/gallium/state_trackers/egl/</code>.</p>
200
201<p>The suggested way to learn to write a EGL driver is to see how other drivers
202are written. <code>egl_glx</code> should be a good reference. It works in any
203environment that has GLX support, and it is simpler than most drivers.</p>
204
205<h3>Lifetime of Display Resources</h3>
206
207<p>Contexts and surfaces are examples of display resources. They might live
208longer than the display that creates them.</p>
209
210<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
211display resources should be destroyed. Similarly, when a thread is released
212throught <code>eglReleaseThread</code>, all current display resources should be
213released. Another way to destory or release resources is through functions
214such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
215
216<p>When a resource that is current to some thread is destroyed, the resource
217should not be destroyed immediately. EGL requires the resource to live until
218it is no longer current. A driver usually calls
219<code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
220(current) to any thread in the destroy callbacks. If it is still bound, the
221resource is not destroyed.</p>
222
223<p>The main library will mark destroyed current resources as unlinked. In a
224driver's <code>MakeCurrent</code> callback,
225<code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
226released resource is linked to a display. If it is not, the last reference to
227the resource is removed and the driver should destroy the resource. But it
228should be careful here because <code>MakeCurrent</code> might be called with an
229uninitialized display.</p>
230
231<p>This is the only mechanism provided by the main library to help manage the
232resources. The drivers are responsible to the correct behavior as defined by
233EGL.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]234
Chia-I Wu1b2b08c2010-02-05 12:44:45 +0800[diff] [blame]235<h3><code>EGL_RENDER_BUFFER</code></h3>
236
237<p>In EGL, the color buffer a context should try to render to is decided by the
238binding surface. It should try to render to the front buffer if the binding
239surface has <code>EGL_RENDER_BUFFER</code> set to
240<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
241surface with <code>EGL_RENDER_BUFFER</code> set to
242<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
243buffer. However, the context is allowed to make the final decision as to which
244color buffer it wants to or is able to render to.</p>
245
246<p>For pbuffer surfaces, the render buffer is always
247<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
248always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
249requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
250result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
251<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
252config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
253pbuffer surfaces.</p>
254
255<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
256single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
257is desirable that a driver allocates a private color buffer for each pbuffer
258surface created. If the window system the driver supports has native pbuffers,
259or if the native pixmaps have more than one color buffers, the driver should
260carefully attach the native color buffers to the EGL surfaces, re-route them if
261required.</p>
262
263<p>There is no defined behavior as to, for example, how
264<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
265now, it is desired that the draw buffer in a client API be fixed for pixmap and
266pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
267client API renders to the specified render buffer for pixmap and pbuffer
268surfaces.</p>
269
Chia-I Wue16f5772010-02-17 19:52:29 +0800[diff] [blame]270<h3><code>EGLDisplay</code> Mutex</h3>
271
272The <code>EGLDisplay</code> will be locked before calling any of the dispatch
273functions (well, except for GetProcAddress which does not take an
274<code>EGLDisplay</code>). This guarantees that the same dispatch function will
275not be called with the sample display at the same time. If a driver has access
276to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
277should as well lock the display before using it.
278
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]279<h3>TODOs</h3>
280
281<ul>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]282<li>Pass the conformance tests</li>
Chia-I Wu68071822010-09-09 13:51:59 +0800[diff] [blame]283<li>Mixed use of OpenGL, OpenGL ES 1.1, and OpenGL ES 2.0 is supported. But
284which one of <code>libGL.so</code>, <code>libGLESv1_CM.so</code>, and
285<code>libGLESv2.so</code> should an application link to? Bad things may happen
286when, say, an application is linked to <code>libGLESv2.so</code> and
287<code>libcairo</code>, which is linked to <code>libGL.so</code> instead.</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]288
289</ul>
290
291</body>
292</html>