<p>The current version of EGL in Mesa implements EGL 1.4. More information
about EGL can be found at
-<a href="http://www.khronos.org/egl/">http://www.khronos.org/egl/</a>.</p>
+<a href="http://www.khronos.org/egl/" target="_parent">
+http://www.khronos.org/egl/</a>.</p>
<p>The Mesa's implementation of EGL uses a driver architecture. The main
library (<code>libEGL</code>) is window system neutral. It provides the EGL
the Gallium driver for your hardware. For example</p>
<pre>
- $ ./configure --with-state-trackers=egl_g3d,es,vega --enable-gallium-intel
+ $ ./configure --with-state-trackers=egl,es,vega --enable-gallium-{swrast,intel}
</pre>
-<p>The main library will be enabled by default. The <code>egl_g3d</code> state
+<p>The main library will be enabled by default. The <code>egl</code> state
tracker is needed by a number of EGL drivers. EGL drivers will be covered
later. The <a href="opengles.html">es state tracker</a> provides OpenGL ES 1.x
and 2.x and the <a href="openvg.html">vega state tracker</a> provides OpenVG
</li>
+<li><code>--with-egl-driver-dir</code>
+
+<p>The directory EGL drivers should be installed to. If not specified, EGL
+drivers will be installed to <code>${libdir}/egl</code>.</p>
+
+</li>
+
<li><code>--with-egl-displays</code>
<p>List the window system(s) to support. It is by default <code>x11</code>,
<p>The argument is a comma separated string. It is usually used to specify the
rendering APIs, like OpenGL ES or OpenVG, to build. But it should be noted
-that a number of EGL drivers depend on the <code>egl_g3d</code> state tracker.
-They will <em>not</em> be built without the <code>egl_g3d</code> state
-tracker.</p>
+that a number of EGL drivers depend on the <code>egl</code> state tracker.
+They will <em>not</em> be built without the <code>egl</code> state tracker.</p>
+
+</li>
+
+<li><code>--enable-gallium-swrast</code>
+
+<p>This option is not specific to EGL. But if there is no driver for your
+hardware, or you are experiencing problems with the hardware driver, you can
+enable the swrast DRM driver. It is a dummy driver and EGL will fallback to
+software rendering automatically.</p>
</li>
</ul>
runtime</p>
<ul>
+<li><code>EGL_DRIVERS_PATH</code>
+
+<p>By default, the main library will look for drivers in the directory where
+the drivers are installed to. This variable specifies a list of
+colon-separated directories where the main library will look for drivers, in
+addition to the default directory. This variable is ignored for setuid/setgid
+binaries.</p>
+
+</li>
+
<li><code>EGL_DRIVER</code>
-<p>This variable forces the specified EGL driver to be loaded. It comes in
-handy when one wants to test a specific driver.</p>
+<p>This variable specifies a full path to an EGL driver and it forces the
+specified EGL driver to be loaded. It comes in handy when one wants to test a
+specific driver. This variable is ignored for setuid/setgid binaries.</p>
</li>
<p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4. The
support for optional EGL functions and EGL extensions is usually more complete
-than the classic ones. These drivers depend on the <code>egl_g3d</code> state
+than the classic ones. These drivers depend on the <code>egl</code> state
tracker to build. The available drivers are</p>
<ul>
<li><code>egl_<dpy>_i965</code></li>
<li><code>egl_<dpy>_radeon</code></li>
<li><code>egl_<dpy>_nouveau</code></li>
+<li><code>egl_<dpy>_swrast</code></li>
<li><code>egl_<dpy>_vmwgfx</code></li>
</ul>
is not available in GLX or GLX extensions.</p>
</li>
-<li><code>egl_xdri</code>
+<li><code>egl_dri2</code>
<p>This driver supports the X Window System as its window system. It functions
-as a DRI driver loader. Unlike <code>egl_glx</code>, it has no dependency on
-<code>libGL</code>. It talks to the X server directly using DRI or DRI2
-protocols. It also talks minimal GLX protocol for things like available
-visuals or fbconfigs. With direct access to the DRI drivers, it has the
-potential to support more EGL functions that are not possible with
-<code>egl_glx</code></p>
+as a DRI2 driver loader. Unlike <code>egl_glx</code>, it has no dependency on
+<code>libGL</code>. It talks to the X server directly using DRI2 protocol.</p>
</li>
<li><code>egl_dri</code>
<p>This driver lacks maintenance and does <em>not</em> build. It is similiar
-to <code>egl_xdri</code> in that it functions as a DRI driver loader. But
-unlike <code>egl_xdri</code>, it supports Linux framebuffer devices as its
-window system and supports EGL_MESA_screen_surface extension. It loads only
-DRI1 drivers. As DRI1 drivers is phasing out, it might be better to rewrite
-the driver to support KMS and DRI2.</p>
+to <code>egl_dri2</code> in that it functions as a DRI(1) driver loader. But
+unlike <code>egl_dri2</code>, it supports Linux framebuffer devices as its
+window system and supports EGL_MESA_screen_surface extension. As DRI1 drivers
+are phasing out, it might eventually be replaced by <code>egl_dri2</code>.</p>
</li>
</ul>
<h2>Developers</h2>
-The sources of the main library and the classic drivers can be found at
-<code>src/egl/</code>. The sources of the <code>egl_g3d</code> state tracker
-can be found at <code>src/gallium/state_trackers/egl_g3d/</code>.
+<p>The sources of the main library and the classic drivers can be found at
+<code>src/egl/</code>. The sources of the <code>egl</code> state tracker can
+be found at <code>src/gallium/state_trackers/egl/</code>.</p>
+
+<p>The suggested way to learn to write a EGL driver is to see how other drivers
+are written. <code>egl_glx</code> should be a good reference. It works in any
+environment that has GLX support, and it is simpler than most drivers.</p>
+
+<h3>Lifetime of Display Resources</h3>
+
+<p>Contexts and surfaces are examples of display resources. They might live
+longer than the display that creates them.</p>
+
+<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
+display resources should be destroyed. Similarly, when a thread is released
+throught <code>eglReleaseThread</code>, all current display resources should be
+released. Another way to destory or release resources is through functions
+such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
+
+<p>When a resource that is current to some thread is destroyed, the resource
+should not be destroyed immediately. EGL requires the resource to live until
+it is no longer current. A driver usually calls
+<code>eglIs<Resource>Bound</code> to check if a resource is bound
+(current) to any thread in the destroy callbacks. If it is still bound, the
+resource is not destroyed.</p>
+
+<p>The main library will mark destroyed current resources as unlinked. In a
+driver's <code>MakeCurrent</code> callback,
+<code>eglIs<Resource>Linked</code> can then be called to check if a newly
+released resource is linked to a display. If it is not, the last reference to
+the resource is removed and the driver should destroy the resource. But it
+should be careful here because <code>MakeCurrent</code> might be called with an
+uninitialized display.</p>
+
+<p>This is the only mechanism provided by the main library to help manage the
+resources. The drivers are responsible to the correct behavior as defined by
+EGL.</p>
+
+<h3><code>EGL_RENDER_BUFFER</code></h3>
+
+<p>In EGL, the color buffer a context should try to render to is decided by the
+binding surface. It should try to render to the front buffer if the binding
+surface has <code>EGL_RENDER_BUFFER</code> set to
+<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
+surface with <code>EGL_RENDER_BUFFER</code> set to
+<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
+buffer. However, the context is allowed to make the final decision as to which
+color buffer it wants to or is able to render to.</p>
+
+<p>For pbuffer surfaces, the render buffer is always
+<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
+always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
+requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
+result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
+<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
+config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
+pbuffer surfaces.</p>
+
+<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
+single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
+is desirable that a driver allocates a private color buffer for each pbuffer
+surface created. If the window system the driver supports has native pbuffers,
+or if the native pixmaps have more than one color buffers, the driver should
+carefully attach the native color buffers to the EGL surfaces, re-route them if
+required.</p>
+
+<p>There is no defined behavior as to, for example, how
+<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
+now, it is desired that the draw buffer in a client API be fixed for pixmap and
+pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
+client API renders to the specified render buffer for pixmap and pbuffer
+surfaces.</p>
<h3>TODOs</h3>
projects / mesa.git / blobdiff