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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	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	32	$ ./configure --enable-gles2 --enable-openvg --enable-gallium-nouveau
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	33	</pre>
				34
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	35	<p>The main library and OpenGL is enabled by default. The first option above
				36	enables <a href="opengles.html">OpenGL ES 2.x</a>. The second option enables
				37	<a href="openvg.html">OpenVG</a>.</p>
Chia-I Wu	c6320c5	2010-10-28 17:25:07 +0800	[diff] [blame]	38
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	39	</li>
				40
				41	<li>Build and install Mesa as usual.</li>
				42	</ol>
				43
				44	<p>In the given example, it will build and install <code>libEGL</code>,
Chia-I Wu	2e3c4e4	2010-05-07 14:13:08 +0800	[diff] [blame]	45	<code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>,
				46	<code>libOpenVG</code>, and one or more EGL drivers.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	47
				48	<h3>Configure Options</h3>
				49
				50	<p>There are several options that control the build of EGL at configuration
				51	time</p>
				52
				53	<ul>
				54	<li><code>--enable-egl</code>
				55
				56	<p>By default, EGL is enabled. When disabled, the main library and the drivers
				57	will not be built.</p>
				58
				59	</li>
				60
Chia-I Wu	a6342af	2010-01-26 10:54:45 +0800	[diff] [blame]	61	<li><code>--with-egl-driver-dir</code>
				62
				63	<p>The directory EGL drivers should be installed to. If not specified, EGL
				64	drivers will be installed to <code>${libdir}/egl</code>.</p>
				65
				66	</li>
				67
Chia-I Wu	da39d5d	2010-06-17 16:07:46 +0800	[diff] [blame]	68	<li><code>--with-egl-platforms</code>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	69
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	70	<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]	71	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]	72	the platforms a driver may support. The first listed platform is also used by
				73	the main library to decide the native platform: the platform the EGL native
				74	types such as <code>EGLNativeDisplayType</code> or
				75	<code>EGLNativeWindowType</code> defined for.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	76
Chia-I Wu	e7424d7	2010-09-19 16:54:39 +0800	[diff] [blame]	77	<p>The available platforms are <code>x11</code>, <code>drm</code>,
Chia-I Wu	da39d5d	2010-06-17 16:07:46 +0800	[diff] [blame]	78	<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]	79	only be built with SCons. Unless for special needs, the build system should
				80	select the right platforms automatically.</p>
Chia-I Wu	2e3c4e4	2010-05-07 14:13:08 +0800	[diff] [blame]	81
				82	</li>
				83
				84	<li><code>--enable-gles1</code> and <code>--enable-gles2</code>
				85
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame^]	86	<p>These options enable OpenGL ES support in OpenGL. The result is one big
				87	internal library that supports multiple APIs.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	88
				89	</li>
Chia-I Wu	a1306f4	2010-01-22 15:51:51 +0800	[diff] [blame]	90
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	91	<li><code>--enable-gles-overlay</code>
				92
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame^]	93	<p>This option enables OpenGL ES as separate internal libraries. This is an
				94	alternative approach to enable OpenGL ES.</p>
				95
				96	<p>This is only supported by <code>egl_gallium</code>. For systems using DRI
				97	drivers, <code>--enable-gles1</code> and <code>--enable-gles2</code> are
				98	suggested instead as all drivers will benefit.</p>
Chia-I Wu	3418f74	2010-11-02 23:55:56 +0800	[diff] [blame]	99
				100	</li>
				101
Chia-I Wu	c6320c5	2010-10-28 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 Wu	3418f74	2010-11-02 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 Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	114	</ul>
				115
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	116	<h2>Use EGL</h2>
				117
Chia-I Wu	411bba3	2010-06-11 12:47:14 +0800	[diff] [blame]	118	<h3>Demos</h3>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	119
Chia-I Wu	411bba3	2010-06-11 12:47:14 +0800	[diff] [blame]	120	<p>There are demos for the client APIs supported by EGL. They can be found in
				121	mesa/demos repository.</p>
Chia-I Wu	ada4605	2010-01-21 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
				126	runtime</p>
				127
				128	<ul>
Chia-I Wu	5d8646c	2010-02-02 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
				132	the drivers are installed to. This variable specifies a list of
				133	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]	134	addition to the default directory. This variable is ignored for setuid/setgid
				135	binaries.</p>
Chia-I Wu	5d8646c	2010-02-02 15:34:55 +0800	[diff] [blame]	136
				137	</li>
				138
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	139	<li><code>EGL_DRIVER</code>
				140
Chia-I Wu	7fc3581	2010-02-02 11:05:19 +0800	[diff] [blame]	141	<p>This variable specifies a full path to an EGL driver and it forces the
				142	specified EGL driver to be loaded. It comes in handy when one wants to test a
Chia-I Wu	6fd8b6a	2010-02-02 16:47:53 +0800	[diff] [blame]	143	specific driver. This variable is ignored for setuid/setgid binaries.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	144
				145	</li>
				146
Chia-I Wu	da39d5d	2010-06-17 16:07:46 +0800	[diff] [blame]	147	<li><code>EGL_PLATFORM</code>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	148
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	149	<p>This variable specifies the native platform. The valid values are the same
				150	as those for <code>--with-egl-platforms</code>. When the variable is not set,
				151	the main library uses the first platform listed in
Chia-I Wu	3418f74	2010-11-02 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
				155	create displays for non-native platforms. These extensions are usually used by
				156	applications that support non-native platforms. Setting this variable is
				157	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]	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
				164	values 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
				172	variable to true forces the use of software rendering.</p>
				173
				174	</li>
				175	</ul>
				176
				177	<h2>EGL Drivers</h2>
				178
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	179	<ul>
Chia-I Wu	3418f74	2010-11-02 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.
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame^]	183	It functions as a DRI driver loader. For <code>x11</code> support, it talks to
				184	the X server directly using (XCB-)DRI2 protocol.</p>
				185
				186	<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]	187
				188	</li>
				189
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	190	<li><code>egl_gallium</code>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	191
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	192	<p>This driver is based on Gallium3D. It supports all rendering APIs and
				193	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]	194	The supported platforms are X11, DRM, FBDEV, and GDI.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	195
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame^]	196	<p>This driver comes with its own hardware drivers
				197	(<code>pipe_<hw></code>) and client API modules
				198	(<code>st_<api></code>).</p>
				199
Chia-I Wu	b365b15	2010-07-03 17:18:40 +0800	[diff] [blame]	200	</li>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	201
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	202	<li><code>egl_glx</code>
				203
				204	<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
				205	the EGL API. It supports both direct and indirect rendering when the GLX does.
				206	It is accelerated when the GLX is. As such, it cannot provide functions that
				207	is not available in GLX or GLX extensions.</p>
				208	</li>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	209	</ul>
				210
Chia-I Wu	65e8f81	2010-12-25 02:45:13 +0800	[diff] [blame^]	211	<h2>Packaging</h2>
				212
				213	<p>The ABI between the main library and its drivers are not stable. Nor is
				214	there a plan to stabilize it at the moment. Of the EGL drivers,
				215	<code>egl_gallium</code> has its own hardware drivers and client API modules.
				216	They are considered internal to <code>egl_gallium</code> and there is also no
				217	stable ABI between them. These should be kept in mind when packaging for
				218	distribution.</p>
				219
				220	<p>Generally, <code>egl_dri2</code> is preferred over <code>egl_gallium</code>
				221	when the system already has DRI drivers. As <code>egl_gallium</code> is loaded
				222	before <code>egl_dri2</code> when both are available, <code>egl_gallium</code>
				223	may either be disabled with <code>--disable-gallium-egl</code> or packaged
				224	separately.</p>
				225
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	226	<h2>Developers</h2>
				227
Chia-I Wu	14cbf32	2010-01-27 23:18:22 +0800	[diff] [blame]	228	<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]	229	<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]	230	be found at <code>src/gallium/state_trackers/egl/</code>.</p>
				231
				232	<p>The suggested way to learn to write a EGL driver is to see how other drivers
				233	are written. <code>egl_glx</code> should be a good reference. It works in any
				234	environment that has GLX support, and it is simpler than most drivers.</p>
				235
				236	<h3>Lifetime of Display Resources</h3>
				237
				238	<p>Contexts and surfaces are examples of display resources. They might live
				239	longer than the display that creates them.</p>
				240
				241	<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
				242	display resources should be destroyed. Similarly, when a thread is released
				243	throught <code>eglReleaseThread</code>, all current display resources should be
				244	released. Another way to destory or release resources is through functions
				245	such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
				246
				247	<p>When a resource that is current to some thread is destroyed, the resource
				248	should not be destroyed immediately. EGL requires the resource to live until
				249	it is no longer current. A driver usually calls
				250	<code>eglIs<Resource>Bound</code> to check if a resource is bound
				251	(current) to any thread in the destroy callbacks. If it is still bound, the
				252	resource is not destroyed.</p>
				253
				254	<p>The main library will mark destroyed current resources as unlinked. In a
				255	driver's <code>MakeCurrent</code> callback,
				256	<code>eglIs<Resource>Linked</code> can then be called to check if a newly
				257	released resource is linked to a display. If it is not, the last reference to
				258	the resource is removed and the driver should destroy the resource. But it
				259	should be careful here because <code>MakeCurrent</code> might be called with an
				260	uninitialized display.</p>
				261
				262	<p>This is the only mechanism provided by the main library to help manage the
				263	resources. The drivers are responsible to the correct behavior as defined by
				264	EGL.</p>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	265
Chia-I Wu	1b2b08c	2010-02-05 12:44:45 +0800	[diff] [blame]	266	<h3><code>EGL_RENDER_BUFFER</code></h3>
				267
				268	<p>In EGL, the color buffer a context should try to render to is decided by the
				269	binding surface. It should try to render to the front buffer if the binding
				270	surface has <code>EGL_RENDER_BUFFER</code> set to
				271	<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
				272	surface with <code>EGL_RENDER_BUFFER</code> set to
				273	<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
				274	buffer. However, the context is allowed to make the final decision as to which
				275	color buffer it wants to or is able to render to.</p>
				276
				277	<p>For pbuffer surfaces, the render buffer is always
				278	<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
				279	always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
				280	requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
				281	result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
				282	<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
				283	config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
				284	pbuffer surfaces.</p>
				285
				286	<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
				287	single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
				288	is desirable that a driver allocates a private color buffer for each pbuffer
				289	surface created. If the window system the driver supports has native pbuffers,
				290	or if the native pixmaps have more than one color buffers, the driver should
				291	carefully attach the native color buffers to the EGL surfaces, re-route them if
				292	required.</p>
				293
				294	<p>There is no defined behavior as to, for example, how
				295	<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
				296	now, it is desired that the draw buffer in a client API be fixed for pixmap and
				297	pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
				298	client API renders to the specified render buffer for pixmap and pbuffer
				299	surfaces.</p>
				300
Chia-I Wu	e16f577	2010-02-17 19:52:29 +0800	[diff] [blame]	301	<h3><code>EGLDisplay</code> Mutex</h3>
				302
				303	The <code>EGLDisplay</code> will be locked before calling any of the dispatch
				304	functions (well, except for GetProcAddress which does not take an
				305	<code>EGLDisplay</code>). This guarantees that the same dispatch function will
				306	not be called with the sample display at the same time. If a driver has access
				307	to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
				308	should as well lock the display before using it.
				309
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	310	<h3>TODOs</h3>
				311
				312	<ul>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	313	<li>Pass the conformance tests</li>
Chia-I Wu	6807182	2010-09-09 13:51:59 +0800	[diff] [blame]	314	<li>Mixed use of OpenGL, OpenGL ES 1.1, and OpenGL ES 2.0 is supported. But
				315	which one of <code>libGL.so</code>, <code>libGLESv1_CM.so</code>, and
				316	<code>libGLESv2.so</code> should an application link to? Bad things may happen
				317	when, say, an application is linked to <code>libGLESv2.so</code> and
				318	<code>libcairo</code>, which is linked to <code>libGL.so</code> instead.</li>
Chia-I Wu	ada4605	2010-01-21 15:29:14 +0800	[diff] [blame]	319
				320	</ul>
				321
				322	</body>
				323	</html>