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11 The Mesa
3D Graphics Library
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19 <p>The current version of EGL in Mesa implements EGL
1.4. More information
20 about EGL can be found at
21 <a href=
"https://www.khronos.org/egl/">
22 https://www.khronos.org/egl/
</a>.
</p>
24 <p>The Mesa's implementation of EGL uses a driver architecture. The main
25 library (
<code>libEGL
</code>) is window system neutral. It provides the EGL
26 API entry points and helper functions for use by the drivers. Drivers are
27 dynamically loaded by the main library and most of the EGL API calls are
28 directly dispatched to the drivers.
</p>
30 <p>The driver in use decides the window system to support.
</p>
36 <p>Configure your build with the desired client APIs and enable
37 the driver for your hardware. For example:
</p>
45 -D gallium-drivers=...
48 <p>The main library and OpenGL is enabled by default. The first two options
49 above enables
<a href=
"opengles.html">OpenGL ES
1.x and
2.x
</a>. The last two
50 options enables the listed classic and Gallium drivers respectively.
</p>
54 <li>Build and install Mesa as usual.
</li>
57 <p>In the given example, it will build and install
<code>libEGL
</code>,
58 <code>libGL
</code>,
<code>libGLESv1_CM
</code>,
<code>libGLESv2
</code>, and one
59 or more EGL drivers.
</p>
61 <h3>Configure Options
</h3>
63 <p>There are several options that control the build of EGL at configuration
67 <dt><code>-D egl=true
</code></dt>
70 <p>By default, EGL is enabled. When disabled, the main library and the drivers
71 will not be built.
</p>
75 <dt><code>-D platforms=...
</code></dt>
78 <p>List the platforms (window systems) to support. Its argument is a comma
79 separated string such as
<code>-D platforms=x11,drm
</code>. It decides
80 the platforms a driver may support. The first listed platform is also used by
81 the main library to decide the native platform.
</p>
83 <p>The available platforms are
<code>x11
</code>,
<code>drm
</code>,
84 <code>wayland
</code>,
<code>surfaceless
</code>,
<code>android
</code>,
85 and
<code>haiku
</code>.
86 The
<code>android
</code> platform can either be built as a system
87 component, part of AOSP, using
<code>Android.mk
</code> files, or
88 cross-compiled using appropriate options.
89 The
<code>haiku
</code> platform can only be built with SCons or Meson.
90 Unless for special needs, the build system should
91 select the right platforms automatically.
</p>
95 <dt><code>-D gles1=true
</code></dt>
96 <dt><code>-D gles2=true
</code></dt>
99 <p>These options enable OpenGL ES support in OpenGL. The result is one big
100 internal library that supports multiple APIs.
</p>
104 <dt><code>-D shared-glapi=true
</code></dt>
107 <p>By default,
<code>libGL
</code> has its own copy of
<code>libglapi
</code>.
108 This options makes
<code>libGL
</code> use the shared
<code>libglapi
</code>. This
109 is required if applications mix OpenGL and OpenGL ES.
</p>
119 <p>There are demos for the client APIs supported by EGL. They can be found in
120 mesa/demos repository.
</p>
122 <h3>Environment Variables
</h3>
124 <p>There are several environment variables that control the behavior of EGL at
128 <dt><code>EGL_PLATFORM
</code></dt>
131 <p>This variable specifies the native platform. The valid values are the same
132 as those for
<code>-D platforms=...
</code>. When the variable is not set,
133 the main library uses the first platform listed in
134 <code>-D platforms=...
</code> as the native platform.
</p>
136 <p>Extensions like
<code>EGL_MESA_drm_display
</code> define new functions to
137 create displays for non-native platforms. These extensions are usually used by
138 applications that support non-native platforms. Setting this variable is
139 probably required only for some of the demos found in mesa/demo repository.
</p>
143 <dt><code>EGL_LOG_LEVEL
</code></dt>
146 <p>This changes the log level of the main library and the drivers. The valid
147 values are:
<code>debug
</code>,
<code>info
</code>,
<code>warning
</code>, and
148 <code>fatal
</code>.
</p>
156 <dt><code>egl_dri2
</code></dt>
159 <p>This driver supports both
<code>x11
</code> and
<code>drm
</code> platforms.
160 It functions as a DRI driver loader. For
<code>x11
</code> support, it talks to
161 the X server directly using (XCB-)DRI2 protocol.
</p>
163 <p>This driver can share DRI drivers with
<code>libGL
</code>.
</p>
170 <p>The ABI between the main library and its drivers are not stable. Nor is
171 there a plan to stabilize it at the moment.
</p>
175 <p>The sources of the main library and drivers can be found at
176 <code>src/egl/
</code>.
</p>
178 <h3>Lifetime of Display Resources
</h3>
180 <p>Contexts and surfaces are examples of display resources. They might live
181 longer than the display that creates them.
</p>
183 <p>In EGL, when a display is terminated through
<code>eglTerminate
</code>, all
184 display resources should be destroyed. Similarly, when a thread is released
185 through
<code>eglReleaseThread
</code>, all current display resources should be
186 released. Another way to destroy or release resources is through functions
187 such as
<code>eglDestroySurface
</code> or
<code>eglMakeCurrent
</code>.
</p>
189 <p>When a resource that is current to some thread is destroyed, the resource
190 should not be destroyed immediately. EGL requires the resource to live until
191 it is no longer current. A driver usually calls
192 <code>eglIs
<Resource
>Bound
</code> to check if a resource is bound
193 (current) to any thread in the destroy callbacks. If it is still bound, the
194 resource is not destroyed.
</p>
196 <p>The main library will mark destroyed current resources as unlinked. In a
197 driver's
<code>MakeCurrent
</code> callback,
198 <code>eglIs
<Resource
>Linked
</code> can then be called to check if a newly
199 released resource is linked to a display. If it is not, the last reference to
200 the resource is removed and the driver should destroy the resource. But it
201 should be careful here because
<code>MakeCurrent
</code> might be called with an
202 uninitialized display.
</p>
204 <p>This is the only mechanism provided by the main library to help manage the
205 resources. The drivers are responsible to the correct behavior as defined by
208 <h3><code>EGL_RENDER_BUFFER
</code></h3>
210 <p>In EGL, the color buffer a context should try to render to is decided by the
211 binding surface. It should try to render to the front buffer if the binding
212 surface has
<code>EGL_RENDER_BUFFER
</code> set to
213 <code>EGL_SINGLE_BUFFER
</code>; If the same context is later bound to a
214 surface with
<code>EGL_RENDER_BUFFER
</code> set to
215 <code>EGL_BACK_BUFFER
</code>, the context should try to render to the back
216 buffer. However, the context is allowed to make the final decision as to which
217 color buffer it wants to or is able to render to.
</p>
219 <p>For pbuffer surfaces, the render buffer is always
220 <code>EGL_BACK_BUFFER
</code>. And for pixmap surfaces, the render buffer is
221 always
<code>EGL_SINGLE_BUFFER
</code>. Unlike window surfaces, EGL spec
222 requires their
<code>EGL_RENDER_BUFFER
</code> values to be honored. As a
223 result, a driver should never set
<code>EGL_PIXMAP_BIT
</code> or
224 <code>EGL_PBUFFER_BIT
</code> bits of a config if the contexts created with the
225 config won't be able to honor the
<code>EGL_RENDER_BUFFER
</code> of pixmap or
226 pbuffer surfaces.
</p>
228 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
229 single-buffered, in that
<code>eglSwapBuffers
</code> has no effect on them. It
230 is desirable that a driver allocates a private color buffer for each pbuffer
231 surface created. If the window system the driver supports has native pbuffers,
232 or if the native pixmaps have more than one color buffers, the driver should
233 carefully attach the native color buffers to the EGL surfaces, re-route them if
236 <p>There is no defined behavior as to, for example, how
237 <code>glDrawBuffer
</code> interacts with
<code>EGL_RENDER_BUFFER
</code>. Right
238 now, it is desired that the draw buffer in a client API be fixed for pixmap and
239 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
240 client API renders to the specified render buffer for pixmap and pbuffer
243 <h3><code>EGLDisplay
</code> Mutex
</h3>
245 The
<code>EGLDisplay
</code> will be locked before calling any of the dispatch
246 functions (well, except for GetProcAddress which does not take an
247 <code>EGLDisplay
</code>). This guarantees that the same dispatch function will
248 not be called with the sample display at the same time. If a driver has access
249 to an
<code>EGLDisplay
</code> without going through the EGL APIs, the driver
250 should as well lock the display before using it.