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Chia-I Wu	ada4605	2010-01-21 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
				12	about EGL can be found at
Brian Paul	aeff9f9	2010-01-21 08:13:32 -0700	[diff] [blame]	13	<a href="http://www.khronos.org/egl/" target="_parent">
				14	http://www.khronos.org/egl/</a>.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	15
				16	<p>The Mesa's implementation of EGL uses a driver architecture. The main
				17	library (<code>libEGL</code>) is window system neutral. It provides the EGL
				18	API entry points and helper functions for use by the drivers. Drivers are
				19	dynamically loaded by the main library and most of the EGL API calls are
				20	directly dispatched to the drivers.</p>
				21
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame]	22	<p>The driver in use decides the window system to support.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	23
				24	<h2>Build EGL</h2>
				25
				26	<ol>
				27	<li>
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	28	<p>Run <code>configure</code> with the desired client APIs and enable
				29	the driver for your hardware. For example</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	30
				31	<pre>
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	32	$ ./configure --enable-gles1 --enable-gles2 \
				33	--with-dri-drivers=... \
				34	--with-gallium-drivers=...
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	35	</pre>
				36
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	37	<p>The main library and OpenGL is enabled by default. The first two options
				38	above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The last two
				39	options enables the listed classic and and Gallium drivers respectively.</p>
Chia-I Wu	c6320c5	2010-10-28 17:25:07 +0800	[diff] [blame]	40
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	41	</li>
				42
				43	<li>Build and install Mesa as usual.</li>
				44	</ol>
				45
				46	<p>In the given example, it will build and install <code>libEGL</code>,
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	47	<code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>, and one
				48	or more EGL drivers.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	49
				50	<h3>Configure Options</h3>
				51
				52	<p>There are several options that control the build of EGL at configuration
				53	time</p>
				54
				55	<ul>
				56	<li><code>--enable-egl</code>
				57
				58	<p>By default, EGL is enabled. When disabled, the main library and the drivers
				59	will not be built.</p>
				60
				61	</li>
				62
Chia-I Wu	a6342af	2010-01-26 10:54:45 +0800	[diff] [blame]	63	<li><code>--with-egl-driver-dir</code>
				64
				65	<p>The directory EGL drivers should be installed to. If not specified, EGL
				66	drivers will be installed to <code>${libdir}/egl</code>.</p>
				67
				68	</li>
				69
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	70	<li><code>--enable-gallium-egl</code>
				71
				72	<p>Enable the optional <code>egl_gallium</code> driver.</p>
				73
				74	</li>
				75
Chia-I Wu	da39d5d	2010-06-17 16:07:46 +0800	[diff] [blame]	76	<li><code>--with-egl-platforms</code>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	77
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	78	<p>List the platforms (window systems) to support. Its argument is a comma
Chia-I Wu	e7424d7	2010-09-19 16:54:39 +0800	[diff] [blame]	79	seprated string such as <code>--with-egl-platforms=x11,drm</code>. It decides
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	80	the platforms a driver may support. The first listed platform is also used by
				81	the main library to decide the native platform: the platform the EGL native
				82	types such as <code>EGLNativeDisplayType</code> or
				83	<code>EGLNativeWindowType</code> defined for.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	84
Chia-I Wu	e7424d7	2010-09-19 16:54:39 +0800	[diff] [blame]	85	<p>The available platforms are <code>x11</code>, <code>drm</code>,
Chia-I Wu	da39d5d	2010-06-17 16:07:46 +0800	[diff] [blame]	86	<code>fbdev</code>, and <code>gdi</code>. The <code>gdi</code> platform can
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	87	only be built with SCons. Unless for special needs, the build system should
				88	select the right platforms automatically.</p>
Chia-I Wu	2e3c4e4	2010-05-07 14:13:08 +0800	[diff] [blame]	89
				90	</li>
				91
				92	<li><code>--enable-gles1</code> and <code>--enable-gles2</code>
				93
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame]	94	<p>These options enable OpenGL ES support in OpenGL. The result is one big
				95	internal library that supports multiple APIs.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	96
				97	</li>
Chia-I Wu	a1306f4	2010-01-22 15:51:51 +0800	[diff] [blame]	98
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	99	<li><code>--enable-shared-glapi</code>
Chia-I Wu	c6320c5	2010-10-28 17:25:07 +0800	[diff] [blame]	100
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	101	<p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
				102	This options makes <code>libGL</code> use the shared <code>libglapi</code>. This
				103	is required if applications mix OpenGL and OpenGL ES.</p>
Chia-I Wu	c6320c5	2010-10-28 17:25:07 +0800	[diff] [blame]	104
				105	</li>
				106
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	107	<li><code>--enable-openvg</code>
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	108
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	109	<p>OpenVG must be explicitly enabled by this option.</p>
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	110
				111	</li>
				112
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	113	</ul>
				114
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	115	<h2>Use EGL</h2>
				116
Chia-I Wu	411bba3	2010-06-11 12:47:14 +0800	[diff] [blame]	117	<h3>Demos</h3>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	118
Chia-I Wu	411bba3	2010-06-11 12:47:14 +0800	[diff] [blame]	119	<p>There are demos for the client APIs supported by EGL. They can be found in
				120	mesa/demos repository.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	121
				122	<h3>Environment Variables</h3>
				123
				124	<p>There are several environment variables that control the behavior of EGL at
				125	runtime</p>
				126
				127	<ul>
Chia-I Wu	5d8646c	2010-02-02 15:34:55 +0800	[diff] [blame]	128	<li><code>EGL_DRIVERS_PATH</code>
				129
				130	<p>By default, the main library will look for drivers in the directory where
				131	the drivers are installed to. This variable specifies a list of
				132	colon-separated directories where the main library will look for drivers, in
Chia-I Wu	6fd8b6a	2010-02-02 16:47:53 +0800	[diff] [blame]	133	addition to the default directory. This variable is ignored for setuid/setgid
				134	binaries.</p>
Chia-I Wu	5d8646c	2010-02-02 15:34:55 +0800	[diff] [blame]	135
Chia-I Wu	cba7786	2011-01-04 00:53:19 +0800	[diff] [blame]	136	<p>This variable is usually set to test an uninstalled build. For example, one
				137	may set</p>
				138
				139	<pre>
				140	$ export LD_LIBRARY_PATH=$mesa/lib
				141	$ export EGL_DRIVERS_PATH=$mesa/lib/egl
				142	</pre>
				143
				144	<p>to test a build without installation</p>
				145
Chia-I Wu	5d8646c	2010-02-02 15:34:55 +0800	[diff] [blame]	146	</li>
				147
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	148	<li><code>EGL_DRIVER</code>
				149
Chia-I Wu	c98ea26	2011-01-07 16:30:08 +0800	[diff] [blame]	150	<p>This variable specifies a full path to or the name of an EGL driver. It
				151	forces the specified EGL driver to be loaded. It comes in handy when one wants
				152	to test a specific driver. This variable is ignored for setuid/setgid
				153	binaries.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	154
				155	</li>
				156
Chia-I Wu	da39d5d	2010-06-17 16:07:46 +0800	[diff] [blame]	157	<li><code>EGL_PLATFORM</code>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	158
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	159	<p>This variable specifies the native platform. The valid values are the same
				160	as those for <code>--with-egl-platforms</code>. When the variable is not set,
				161	the main library uses the first platform listed in
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	162	<code>--with-egl-platforms</code> as the native platform.</p>
				163
				164	<p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
				165	create displays for non-native platforms. These extensions are usually used by
				166	applications that support non-native platforms. Setting this variable is
				167	probably required only for some of the demos found in mesa/demo repository.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	168
				169	</li>
				170
				171	<li><code>EGL_LOG_LEVEL</code>
				172
				173	<p>This changes the log level of the main library and the drivers. The valid
				174	values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
				175	<code>fatal</code>.</p>
				176
				177	</li>
				178
				179	<li><code>EGL_SOFTWARE</code>
				180
				181	<p>For drivers that support both hardware and software rendering, setting this
				182	variable to true forces the use of software rendering.</p>
				183
				184	</li>
				185	</ul>
				186
				187	<h2>EGL Drivers</h2>
				188
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	189	<ul>
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	190	<li><code>egl_dri2</code>
				191
				192	<p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame]	193	It functions as a DRI driver loader. For <code>x11</code> support, it talks to
				194	the X server directly using (XCB-)DRI2 protocol.</p>
				195
				196	<p>This driver can share DRI drivers with <code>libGL</code>.</p>
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	197
				198	</li>
				199
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	200	<li><code>egl_gallium</code>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	201
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	202	<p>This driver is based on Gallium3D. It supports all rendering APIs and
				203	hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
Chia-I Wu	c6320c5	2010-10-28 17:25:07 +0800	[diff] [blame]	204	The supported platforms are X11, DRM, FBDEV, and GDI.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	205
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame]	206	<p>This driver comes with its own hardware drivers
				207	(<code>pipe_<hw></code>) and client API modules
				208	(<code>st_<api></code>).</p>
				209
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	210	</li>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	211
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	212	<li><code>egl_glx</code>
				213
				214	<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
				215	the EGL API. It supports both direct and indirect rendering when the GLX does.
				216	It is accelerated when the GLX is. As such, it cannot provide functions that
				217	is not available in GLX or GLX extensions.</p>
				218	</li>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	219	</ul>
				220
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame]	221	<h2>Packaging</h2>
				222
				223	<p>The ABI between the main library and its drivers are not stable. Nor is
				224	there a plan to stabilize it at the moment. Of the EGL drivers,
				225	<code>egl_gallium</code> has its own hardware drivers and client API modules.
				226	They are considered internal to <code>egl_gallium</code> and there is also no
				227	stable ABI between them. These should be kept in mind when packaging for
				228	distribution.</p>
				229
				230	<p>Generally, <code>egl_dri2</code> is preferred over <code>egl_gallium</code>
				231	when the system already has DRI drivers. As <code>egl_gallium</code> is loaded
				232	before <code>egl_dri2</code> when both are available, <code>egl_gallium</code>
Chia-I Wu	8eea050	2011-06-20 11:14:56 +0900	[diff] [blame]	233	is disabled by default.</p>
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame]	234
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	235	<h2>Developers</h2>
				236
Chia-I Wu	14cbf32	2010-01-27 23:18:22 +0800	[diff] [blame]	237	<p>The sources of the main library and the classic drivers can be found at
Chia-I Wu	3c967a9	2010-01-22 16:31:43 +0800	[diff] [blame]	238	<code>src/egl/</code>. The sources of the <code>egl</code> state tracker can
Chia-I Wu	14cbf32	2010-01-27 23:18:22 +0800	[diff] [blame]	239	be found at <code>src/gallium/state_trackers/egl/</code>.</p>
				240
				241	<p>The suggested way to learn to write a EGL driver is to see how other drivers
				242	are written. <code>egl_glx</code> should be a good reference. It works in any
				243	environment that has GLX support, and it is simpler than most drivers.</p>
				244
				245	<h3>Lifetime of Display Resources</h3>
				246
				247	<p>Contexts and surfaces are examples of display resources. They might live
				248	longer than the display that creates them.</p>
				249
				250	<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
				251	display resources should be destroyed. Similarly, when a thread is released
				252	throught <code>eglReleaseThread</code>, all current display resources should be
				253	released. Another way to destory or release resources is through functions
				254	such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
				255
				256	<p>When a resource that is current to some thread is destroyed, the resource
				257	should not be destroyed immediately. EGL requires the resource to live until
				258	it is no longer current. A driver usually calls
				259	<code>eglIs<Resource>Bound</code> to check if a resource is bound
				260	(current) to any thread in the destroy callbacks. If it is still bound, the
				261	resource is not destroyed.</p>
				262
				263	<p>The main library will mark destroyed current resources as unlinked. In a
				264	driver's <code>MakeCurrent</code> callback,
				265	<code>eglIs<Resource>Linked</code> can then be called to check if a newly
				266	released resource is linked to a display. If it is not, the last reference to
				267	the resource is removed and the driver should destroy the resource. But it
				268	should be careful here because <code>MakeCurrent</code> might be called with an
				269	uninitialized display.</p>
				270
				271	<p>This is the only mechanism provided by the main library to help manage the
				272	resources. The drivers are responsible to the correct behavior as defined by
				273	EGL.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	274
Chia-I Wu	1b2b08c	2010-02-05 12:44:45 +0800	[diff] [blame]	275	<h3><code>EGL_RENDER_BUFFER</code></h3>
				276
				277	<p>In EGL, the color buffer a context should try to render to is decided by the
				278	binding surface. It should try to render to the front buffer if the binding
				279	surface has <code>EGL_RENDER_BUFFER</code> set to
				280	<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
				281	surface with <code>EGL_RENDER_BUFFER</code> set to
				282	<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
				283	buffer. However, the context is allowed to make the final decision as to which
				284	color buffer it wants to or is able to render to.</p>
				285
				286	<p>For pbuffer surfaces, the render buffer is always
				287	<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
				288	always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
				289	requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
				290	result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
				291	<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
				292	config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
				293	pbuffer surfaces.</p>
				294
				295	<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
				296	single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
				297	is desirable that a driver allocates a private color buffer for each pbuffer
				298	surface created. If the window system the driver supports has native pbuffers,
				299	or if the native pixmaps have more than one color buffers, the driver should
				300	carefully attach the native color buffers to the EGL surfaces, re-route them if
				301	required.</p>
				302
				303	<p>There is no defined behavior as to, for example, how
				304	<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
				305	now, it is desired that the draw buffer in a client API be fixed for pixmap and
				306	pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
				307	client API renders to the specified render buffer for pixmap and pbuffer
				308	surfaces.</p>
				309
Chia-I Wu	e16f577	2010-02-17 19:52:29 +0800	[diff] [blame]	310	<h3><code>EGLDisplay</code> Mutex</h3>
				311
				312	The <code>EGLDisplay</code> will be locked before calling any of the dispatch
				313	functions (well, except for GetProcAddress which does not take an
				314	<code>EGLDisplay</code>). This guarantees that the same dispatch function will
				315	not be called with the sample display at the same time. If a driver has access
				316	to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
				317	should as well lock the display before using it.
				318
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	319	</body>
				320	</html>