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 client APIs and enable
32 the driver for your hardware. For example</p>
35 $ ./configure --enable-gles2 --enable-openvg --enable-gallium-nouveau
38 <p>The main library and OpenGL is enabled by default. The first option above
39 enables <a href="opengles.html">OpenGL ES 2.x</a>. The second option enables
40 <a href="openvg.html">OpenVG</a>.</p>
44 <li>Build and install Mesa as usual.</li>
47 <p>In the given example, it will build and install <code>libEGL</code>,
48 <code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>,
49 <code>libOpenVG</code>, and one or more EGL drivers.</p>
51 <h3>Configure Options</h3>
53 <p>There are several options that control the build of EGL at configuration
57 <li><code>--enable-egl</code>
59 <p>By default, EGL is enabled. When disabled, the main library and the drivers
60 will not be built.</p>
64 <li><code>--with-egl-driver-dir</code>
66 <p>The directory EGL drivers should be installed to. If not specified, EGL
67 drivers will be installed to <code>${libdir}/egl</code>.</p>
71 <li><code>--with-egl-platforms</code>
73 <p>List the platforms (window systems) to support. Its argument is a comma
74 seprated string such as <code>--with-egl-platforms=x11,drm</code>. It decides
75 the platforms a driver may support. The first listed platform is also used by
76 the main library to decide the native platform: the platform the EGL native
77 types such as <code>EGLNativeDisplayType</code> or
78 <code>EGLNativeWindowType</code> defined for.</p>
80 <p>The available platforms are <code>x11</code>, <code>drm</code>,
81 <code>fbdev</code>, and <code>gdi</code>. The <code>gdi</code> platform can
82 only be built with SCons. Unless for special needs, the build system should
83 select the right platforms automatically.</p>
87 <li><code>--enable-gles1</code> and <code>--enable-gles2</code>
89 <p>These options enable OpenGL ES support in OpenGL. The result is
90 one big library that supports multiple APIs.</p>
94 <li><code>--enable-gles-overlay</code>
96 <p>This option enables OpenGL ES as separate libraries. This is an alternative
97 approach to enable OpenGL ES. It is only supported by
98 <code>egl_gallium</code>.</p>
102 <li><code>--enable-openvg</code>
104 <p>OpenVG must be explicitly enabled by this option.</p>
108 <li><code>--enable-gallium-egl</code>
110 <p>Explicitly enable or disable <code>egl_gallium</code>.</p>
120 <p>There are demos for the client APIs supported by EGL. They can be found in
121 mesa/demos repository.</p>
123 <h3>Environment Variables</h3>
125 <p>There are several environment variables that control the behavior of EGL at
129 <li><code>EGL_DRIVERS_PATH</code>
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
134 addition to the default directory. This variable is ignored for setuid/setgid
139 <li><code>EGL_DRIVER</code>
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
143 specific driver. This variable is ignored for setuid/setgid binaries.</p>
147 <li><code>EGL_PLATFORM</code>
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
152 <code>--with-egl-platforms</code> as the native platform.</p>
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>
161 <li><code>EGL_LOG_LEVEL</code>
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>
169 <li><code>EGL_SOFTWARE</code>
171 <p>For drivers that support both hardware and software rendering, setting this
172 variable to true forces the use of software rendering.</p>
180 <li><code>egl_dri2</code>
182 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
183 It functions as a DRI2 driver loader. For <code>x11</code> support, it talks
184 to the X server directly using (XCB-)DRI2 protocol.</p>
188 <li><code>egl_gallium</code>
190 <p>This driver is based on Gallium3D. It supports all rendering APIs and
191 hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
192 The supported platforms are X11, DRM, FBDEV, and GDI.</p>
196 <li><code>egl_glx</code>
198 <p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
199 the EGL API. It supports both direct and indirect rendering when the GLX does.
200 It is accelerated when the GLX is. As such, it cannot provide functions that
201 is not available in GLX or GLX extensions.</p>
207 <p>The sources of the main library and the classic drivers can be found at
208 <code>src/egl/</code>. The sources of the <code>egl</code> state tracker can
209 be found at <code>src/gallium/state_trackers/egl/</code>.</p>
211 <p>The suggested way to learn to write a EGL driver is to see how other drivers
212 are written. <code>egl_glx</code> should be a good reference. It works in any
213 environment that has GLX support, and it is simpler than most drivers.</p>
215 <h3>Lifetime of Display Resources</h3>
217 <p>Contexts and surfaces are examples of display resources. They might live
218 longer than the display that creates them.</p>
220 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
221 display resources should be destroyed. Similarly, when a thread is released
222 throught <code>eglReleaseThread</code>, all current display resources should be
223 released. Another way to destory or release resources is through functions
224 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
226 <p>When a resource that is current to some thread is destroyed, the resource
227 should not be destroyed immediately. EGL requires the resource to live until
228 it is no longer current. A driver usually calls
229 <code>eglIs<Resource>Bound</code> to check if a resource is bound
230 (current) to any thread in the destroy callbacks. If it is still bound, the
231 resource is not destroyed.</p>
233 <p>The main library will mark destroyed current resources as unlinked. In a
234 driver's <code>MakeCurrent</code> callback,
235 <code>eglIs<Resource>Linked</code> can then be called to check if a newly
236 released resource is linked to a display. If it is not, the last reference to
237 the resource is removed and the driver should destroy the resource. But it
238 should be careful here because <code>MakeCurrent</code> might be called with an
239 uninitialized display.</p>
241 <p>This is the only mechanism provided by the main library to help manage the
242 resources. The drivers are responsible to the correct behavior as defined by
245 <h3><code>EGL_RENDER_BUFFER</code></h3>
247 <p>In EGL, the color buffer a context should try to render to is decided by the
248 binding surface. It should try to render to the front buffer if the binding
249 surface has <code>EGL_RENDER_BUFFER</code> set to
250 <code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
251 surface with <code>EGL_RENDER_BUFFER</code> set to
252 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
253 buffer. However, the context is allowed to make the final decision as to which
254 color buffer it wants to or is able to render to.</p>
256 <p>For pbuffer surfaces, the render buffer is always
257 <code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
258 always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
259 requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
260 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
261 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
262 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
263 pbuffer surfaces.</p>
265 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
266 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
267 is desirable that a driver allocates a private color buffer for each pbuffer
268 surface created. If the window system the driver supports has native pbuffers,
269 or if the native pixmaps have more than one color buffers, the driver should
270 carefully attach the native color buffers to the EGL surfaces, re-route them if
273 <p>There is no defined behavior as to, for example, how
274 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
275 now, it is desired that the draw buffer in a client API be fixed for pixmap and
276 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
277 client API renders to the specified render buffer for pixmap and pbuffer
280 <h3><code>EGLDisplay</code> Mutex</h3>
282 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
283 functions (well, except for GetProcAddress which does not take an
284 <code>EGLDisplay</code>). This guarantees that the same dispatch function will
285 not be called with the sample display at the same time. If a driver has access
286 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
287 should as well lock the display before using it.
292 <li>Pass the conformance tests</li>
293 <li>Mixed use of OpenGL, OpenGL ES 1.1, and OpenGL ES 2.0 is supported. But
294 which one of <code>libGL.so</code>, <code>libGLESv1_CM.so</code>, and
295 <code>libGLESv2.so</code> should an application link to? Bad things may happen
296 when, say, an application is linked to <code>libGLESv2.so</code> and
297 <code>libcairo</code>, which is linked to <code>libGL.so</code> instead.</li>