3 <title>Mesa EGL</title>
5 <head><link rel="stylesheet" type="text/css" href="mesa.css"></head>
11 <p>The current version of EGL in Mesa implements EGL 1.4. More information
12 about EGL can be found at
13 <a href="http://www.khronos.org/egl/" target="_parent">
14 http://www.khronos.org/egl/</a>.</p>
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>
22 <p>The driver in use decides the window system to support. For drivers that
23 support hardware rendering, there are usually multiple drivers supporting the
24 same window system. Each one of of them supports a certain range of graphics
31 <p>Run <code>configure</code> with the desired state trackers and and enable
32 the Gallium driver for your hardware. For example</p>
35 $ ./configure --with-state-trackers=egl,es,vega --enable-gallium-{swrast,intel}
38 <p>The main library will be enabled by default. The <code>egl</code> state
39 tracker is needed by a number of EGL drivers. EGL drivers will be covered
40 later. The <a href="opengles.html">es state tracker</a> provides OpenGL ES 1.x
41 and 2.x and the <a href="openvg.html">vega state tracker</a> provides OpenVG
45 <li>Build and install Mesa as usual.</li>
48 <p>In the given example, it will build and install <code>libEGL</code>,
49 <code>libGLESv1_CM</code>, <code>libGLESv2</code>, <code>libOpenVG</code>, and
50 one or more EGL drivers.</p>
52 <h3>Configure Options</h3>
54 <p>There are several options that control the build of EGL at configuration
58 <li><code>--enable-egl</code>
60 <p>By default, EGL is enabled. When disabled, the main library and the drivers
61 will not be built.</p>
65 <li><code>--with-egl-driver-dir</code>
67 <p>The directory EGL drivers should be installed to. If not specified, EGL
68 drivers will be installed to <code>${libdir}/egl</code>.</p>
72 <li><code>--with-egl-displays</code>
74 <p>List the window system(s) to support. It is by default <code>x11</code>,
75 which supports the X Window System. Its argument is a comma separated string
76 like, for example, <code>--with-egl-displays=x11,kms</code>. Because an EGL
77 driver decides which window system to support, this example will enable two
78 (sets of) EGL drivers. One supports the X window system and the other supports
79 bare KMS (kernel modesetting).</p>
83 <li><code>--with-state-trackers</code>
85 <p>The argument is a comma separated string. It is usually used to specify the
86 rendering APIs, like OpenGL ES or OpenVG, to build. But it should be noted
87 that a number of EGL drivers depend on the <code>egl</code> state tracker.
88 They will <em>not</em> be built without the <code>egl</code> state tracker.</p>
92 <li><code>--enable-gallium-swrast</code>
94 <p>This option is not specific to EGL. But if there is no driver for your
95 hardware, or you are experiencing problems with the hardware driver, you can
96 enable the swrast DRM driver. It is a dummy driver and EGL will fallback to
97 software rendering automatically.</p>
104 <p>The OpenGL state tracker is not built in the above example. It should be
105 noted that the classic <code>libGL</code> is not a state tracker and cannot be
106 used with EGL (unless the EGL driver in use is <code>egl_glx</code>). To build
107 the OpenGL state tracker, one may append <code>glx</code> to
108 <code>--with-state-trackers</code> and manually build
109 <code>src/gallium/winsys/xlib/</code>.</p>
113 <p> The demos for OpenGL ES and OpenVG can be found in <code>progs/es1/</code>,
114 <code>progs/es2/</code> and <code>progs/openvg/</code>. You can use them to
115 test your build. For example,</p>
123 <h3>Environment Variables</h3>
125 <p>There are several environment variables that control the behavior of EGL at
129 <li><code>EGL_DRIVER</code>
131 <p>This variable specifies a full path to an EGL driver and it forces the
132 specified EGL driver to be loaded. It comes in handy when one wants to test a
137 <li><code>EGL_DISPLAY</code>
139 <p>When <code>EGL_DRIVER</code> is not set, the main library loads <em>all</em>
140 EGL drivers that support a certain window system. <code>EGL_DISPLAY</code> can
141 be used to specify the window system and the valid values are, for example,
142 <code>x11</code> or <code>kms</code>. When the variable is not set, the main
143 library defaults the value to the first window system listed in
144 <code>--with-egl-displays</code> at configuration time.
148 <li><code>EGL_LOG_LEVEL</code>
150 <p>This changes the log level of the main library and the drivers. The valid
151 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
152 <code>fatal</code>.</p>
156 <li><code>EGL_SOFTWARE</code>
158 <p>For drivers that support both hardware and software rendering, setting this
159 variable to true forces the use of software rendering.</p>
166 <p>There are two categories of EGL drivers: Gallium and classic.</p>
168 <p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4. The
169 support for optional EGL functions and EGL extensions is usually more complete
170 than the classic ones. These drivers depend on the <code>egl</code> state
171 tracker to build. The available drivers are</p>
174 <li><code>egl_<dpy>_i915</code></li>
175 <li><code>egl_<dpy>_i965</code></li>
176 <li><code>egl_<dpy>_radeon</code></li>
177 <li><code>egl_<dpy>_nouveau</code></li>
178 <li><code>egl_<dpy>_swrast</code></li>
179 <li><code>egl_<dpy>_vmwgfx</code></li>
182 <p><code><dpy></code> is given by <code>--with-egl-displays</code> at
183 configuration time. There will be one EGL driver for each combination of the
184 displays listed and the hardware drivers enabled.</p>
186 <p>Classic EGL drivers, on the other hand, supports only OpenGL as its
187 rendering API. They can be found under <code>src/egl/drivers/</code>. There
191 <li><code>egl_glx</code>
193 <p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
194 the EGL API. It supports both direct and indirect rendering when the GLX does.
195 It is accelerated when the GLX is. As such, it cannot provide functions that
196 is not available in GLX or GLX extensions.</p>
199 <li><code>egl_xdri</code>
201 <p>This driver supports the X Window System as its window system. It functions
202 as a DRI driver loader and can load DRI/DRI2/DRISW drivers. Unlike
203 <code>egl_glx</code>, it has no dependency on <code>libGL</code>. It talks to
204 the X server directly using DRI or DRI2 protocols. It also talks minimal GLX
205 protocol for things like available visuals or fbconfigs. With direct access to
206 the DRI drivers, it has the potential to support more EGL functions that are
207 not possible with <code>egl_glx</code>.</p>
210 <li><code>egl_dri</code>
212 <p>This driver lacks maintenance and does <em>not</em> build. It is similiar
213 to <code>egl_xdri</code> in that it functions as a DRI driver loader. But
214 unlike <code>egl_xdri</code>, it supports Linux framebuffer devices as its
215 window system and supports EGL_MESA_screen_surface extension. It loads only
216 DRI1 drivers. As DRI1 drivers is phasing out, it might be better to rewrite
217 the driver to support KMS and DRI2.</p>
222 <p>To use the classic drivers, one must manually set <code>EGL_DRIVER</code> at
227 <p>The sources of the main library and the classic drivers can be found at
228 <code>src/egl/</code>. The sources of the <code>egl</code> state tracker can
229 be found at <code>src/gallium/state_trackers/egl/</code>.</p>
231 <p>The suggested way to learn to write a EGL driver is to see how other drivers
232 are written. <code>egl_glx</code> should be a good reference. It works in any
233 environment that has GLX support, and it is simpler than most drivers.</p>
235 <h3>Lifetime of Display Resources</h3>
237 <p>Contexts and surfaces are examples of display resources. They might live
238 longer than the display that creates them.</p>
240 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
241 display resources should be destroyed. Similarly, when a thread is released
242 throught <code>eglReleaseThread</code>, all current display resources should be
243 released. Another way to destory or release resources is through functions
244 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
246 <p>When a resource that is current to some thread is destroyed, the resource
247 should not be destroyed immediately. EGL requires the resource to live until
248 it is no longer current. A driver usually calls
249 <code>eglIs<Resource>Bound</code> to check if a resource is bound
250 (current) to any thread in the destroy callbacks. If it is still bound, the
251 resource is not destroyed.</p>
253 <p>The main library will mark destroyed current resources as unlinked. In a
254 driver's <code>MakeCurrent</code> callback,
255 <code>eglIs<Resource>Linked</code> can then be called to check if a newly
256 released resource is linked to a display. If it is not, the last reference to
257 the resource is removed and the driver should destroy the resource. But it
258 should be careful here because <code>MakeCurrent</code> might be called with an
259 uninitialized display.</p>
261 <p>This is the only mechanism provided by the main library to help manage the
262 resources. The drivers are responsible to the correct behavior as defined by
268 <li>Thread safety</li>
269 <li>Pass the conformance tests</li>
270 <li>Better automatic driver selection: <code>EGL_DISPLAY</code> loads all
271 drivers and might eat too much memory.</li>
272 <li>Stop using <code>glxinit.c</code> and sources from <code>src/glx/x11/</code></li>