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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 Wub365b152010-07-03 17:18:40 +0800[diff] [blame]35 $ ./configure --enable-gles-overlay --with-state-trackers=egl,vega --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
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 Wub365b152010-07-03 17:18:40 +0800[diff] [blame]74<p>List the platforms (window systems) to support. Its argument is a comma
75seprated string such as <code>--with-egl-platforms=x11,kms</code>. It decides
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 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 Wub365b152010-07-03 17:18:40 +0800[diff] [blame]90rendering APIs, such as OpenVG, to build. But it is also used to specify
91<code>egl</code> state tracker that <code>egl_gallium</code> depends on.</p>
Chia-I Wu2e3c4e42010-05-07 14:13:08 +0800[diff] [blame]92
93</li>
94
95<li><code>--enable-gles-overlay</code>
96
97<p>OpenGL and OpenGL ES are not controlled by
98<code>--with-state-trackers</code>. OpenGL is always built. To build OpenGL
99ES, this option must be explicitly given.</p>
100
101</li>
102
103<li><code>--enable-gles1</code> and <code>--enable-gles2</code>
104
105<p>Unlike <code>--enable-gles-overlay</code>, which builds one library for each
106rendering API, these options enable OpenGL ES support in OpenGL. The result is
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]107one big library that supports multiple APIs.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]108
109</li>
Chia-I Wua1306f42010-01-22 15:51:51 +0800[diff] [blame]110
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]111</ul>
112
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]113<h2>Use EGL</h2>
114
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]115<h3>Demos</h3>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]116
Chia-I Wu411bba32010-06-11 12:47:14 +0800[diff] [blame]117<p>There are demos for the client APIs supported by EGL. They can be found in
118mesa/demos repository.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]119
120<h3>Environment Variables</h3>
121
122<p>There are several environment variables that control the behavior of EGL at
123runtime</p>
124
125<ul>
Chia-I Wu5d8646c2010-02-02 15:34:55 +0800[diff] [blame]126<li><code>EGL_DRIVERS_PATH</code>
127
128<p>By default, the main library will look for drivers in the directory where
129the drivers are installed to. This variable specifies a list of
130colon-separated directories where the main library will look for drivers, in
Chia-I Wu6fd8b6a2010-02-02 16:47:53 +0800[diff] [blame]131addition to the default directory. This variable is ignored for setuid/setgid
132binaries.</p>
Chia-I Wu5d8646c2010-02-02 15:34:55 +0800[diff] [blame]133
134</li>
135
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]136<li><code>EGL_DRIVER</code>
137
Chia-I Wu7fc35812010-02-02 11:05:19 +0800[diff] [blame]138<p>This variable specifies a full path to an EGL driver and it forces the
139specified 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]140specific driver. This variable is ignored for setuid/setgid binaries.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]141
Chia-I Wu68071822010-09-09 13:51:59 +0800[diff] [blame^]142<p><code>egl_gallium</code> dynamically loads hardware drivers and client API
143modules found in <code>EGL_DRIVERS_PATH</code>. Thus, specifying this variable
144alone is not sufficient for <code>egl_gallium</code> for uninstalled build.</p>
145
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]146</li>
147
Chia-I Wuda39d5d2010-06-17 16:07:46 +0800[diff] [blame]148<li><code>EGL_PLATFORM</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]149
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]150<p>This variable specifies the native platform. The valid values are the same
151as those for <code>--with-egl-platforms</code>. When the variable is not set,
152the main library uses the first platform listed in
153<code>--with-egl-platforms</code> as the native platform</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]154
155</li>
156
157<li><code>EGL_LOG_LEVEL</code>
158
159<p>This changes the log level of the main library and the drivers. The valid
160values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
161<code>fatal</code>.</p>
162
163</li>
164
165<li><code>EGL_SOFTWARE</code>
166
167<p>For drivers that support both hardware and software rendering, setting this
168variable to true forces the use of software rendering.</p>
169
170</li>
171</ul>
172
173<h2>EGL Drivers</h2>
174
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]175<ul>
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]176<li><code>egl_gallium</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]177
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]178<p>This driver is based on Gallium3D. It supports all rendering APIs and
179hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
180The supported platforms are X11, KMS, FBDEV, and GDI.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]181
Chia-I Wub365b152010-07-03 17:18:40 +0800[diff] [blame]182</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]183
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]184<li><code>egl_glx</code>
185
186<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
187the EGL API. It supports both direct and indirect rendering when the GLX does.
188It is accelerated when the GLX is. As such, it cannot provide functions that
189is not available in GLX or GLX extensions.</p>
190</li>
191
Chia-I Wu5f08eff2010-02-05 11:46:28 +0800[diff] [blame]192<li><code>egl_dri2</code>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]193
194<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]195as a DRI2 driver loader. Unlike <code>egl_glx</code>, it has no dependency on
196<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]197
198</li>
199<li><code>egl_dri</code>
200
201<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]202to <code>egl_dri2</code> in that it functions as a DRI(1) driver loader. But
203unlike <code>egl_dri2</code>, it supports Linux framebuffer devices as its
204window system and supports EGL_MESA_screen_surface extension. As DRI1 drivers
205are phasing out, it might eventually be replaced by <code>egl_dri2</code>.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]206
207</li>
208</ul>
209
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]210<h2>Developers</h2>
211
Chia-I Wu14cbf322010-01-27 23:18:22 +0800[diff] [blame]212<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]213<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]214be found at <code>src/gallium/state_trackers/egl/</code>.</p>
215
216<p>The suggested way to learn to write a EGL driver is to see how other drivers
217are written. <code>egl_glx</code> should be a good reference. It works in any
218environment that has GLX support, and it is simpler than most drivers.</p>
219
220<h3>Lifetime of Display Resources</h3>
221
222<p>Contexts and surfaces are examples of display resources. They might live
223longer than the display that creates them.</p>
224
225<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
226display resources should be destroyed. Similarly, when a thread is released
227throught <code>eglReleaseThread</code>, all current display resources should be
228released. Another way to destory or release resources is through functions
229such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
230
231<p>When a resource that is current to some thread is destroyed, the resource
232should not be destroyed immediately. EGL requires the resource to live until
233it is no longer current. A driver usually calls
234<code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
235(current) to any thread in the destroy callbacks. If it is still bound, the
236resource is not destroyed.</p>
237
238<p>The main library will mark destroyed current resources as unlinked. In a
239driver's <code>MakeCurrent</code> callback,
240<code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
241released resource is linked to a display. If it is not, the last reference to
242the resource is removed and the driver should destroy the resource. But it
243should be careful here because <code>MakeCurrent</code> might be called with an
244uninitialized display.</p>
245
246<p>This is the only mechanism provided by the main library to help manage the
247resources. The drivers are responsible to the correct behavior as defined by
248EGL.</p>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]249
Chia-I Wu1b2b08c2010-02-05 12:44:45 +0800[diff] [blame]250<h3><code>EGL_RENDER_BUFFER</code></h3>
251
252<p>In EGL, the color buffer a context should try to render to is decided by the
253binding surface. It should try to render to the front buffer if the binding
254surface has <code>EGL_RENDER_BUFFER</code> set to
255<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
256surface with <code>EGL_RENDER_BUFFER</code> set to
257<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
258buffer. However, the context is allowed to make the final decision as to which
259color buffer it wants to or is able to render to.</p>
260
261<p>For pbuffer surfaces, the render buffer is always
262<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
263always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
264requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
265result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
266<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
267config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
268pbuffer surfaces.</p>
269
270<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
271single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
272is desirable that a driver allocates a private color buffer for each pbuffer
273surface created. If the window system the driver supports has native pbuffers,
274or if the native pixmaps have more than one color buffers, the driver should
275carefully attach the native color buffers to the EGL surfaces, re-route them if
276required.</p>
277
278<p>There is no defined behavior as to, for example, how
279<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
280now, it is desired that the draw buffer in a client API be fixed for pixmap and
281pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
282client API renders to the specified render buffer for pixmap and pbuffer
283surfaces.</p>
284
Chia-I Wue16f5772010-02-17 19:52:29 +0800[diff] [blame]285<h3><code>EGLDisplay</code> Mutex</h3>
286
287The <code>EGLDisplay</code> will be locked before calling any of the dispatch
288functions (well, except for GetProcAddress which does not take an
289<code>EGLDisplay</code>). This guarantees that the same dispatch function will
290not be called with the sample display at the same time. If a driver has access
291to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
292should as well lock the display before using it.
293
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]294<h3>TODOs</h3>
295
296<ul>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]297<li>Pass the conformance tests</li>
Chia-I Wu68071822010-09-09 13:51:59 +0800[diff] [blame^]298<li>Reference counting in main library?</li>
299<li>Mixed use of OpenGL, OpenGL ES 1.1, and OpenGL ES 2.0 is supported. But
300which one of <code>libGL.so</code>, <code>libGLESv1_CM.so</code>, and
301<code>libGLESv2.so</code> should an application link to? Bad things may happen
302when, say, an application is linked to <code>libGLESv2.so</code> and
303<code>libcairo</code>, which is linked to <code>libGL.so</code> instead.</li>
Chia-I Wuada46052010-01-21 15:29:14 +0800[diff] [blame]304
305</ul>
306
307</body>
308</html>