docs/egl.html - platform/external/mesa3d - Gitiles

 <html>

 <title>Mesa EGL</title>

 <head><link rel="stylesheet" type="text/css" href="mesa.css"></head>

 <body>

 <h1>Mesa EGL</h1>

 <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/" 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
 API entry points and helper functions for use by the drivers.  Drivers are
 dynamically loaded by the main library and most of the EGL API calls are
 directly dispatched to the drivers.</p>

 <p>The driver in use decides the window system to support.  For drivers that
 support hardware rendering, there are usually multiple drivers supporting the
 same window system.  Each one of of them supports a certain range of graphics
 cards.</p>

 <h2>Build EGL</h2>

 <ol>
 <li>
 <p>Run <code>configure</code> with the desired state trackers and enable
 the Gallium driver for your hardware.  For example</p>

 <pre>
   $ ./configure --enable-gles-overlay --with-state-trackers=egl,vega --enable-gallium-intel
 </pre>

 <p>The main library and OpenGL is enabled by default.  The first option enables
 <a href="opengles.html">OpenGL ES 1.x and 2.x</a>.  The <code>egl</code> state
 tracker is needed by a number of EGL drivers.  EGL drivers will be covered
 later.  The <a href="openvg.html">vega state tracker</a> provides OpenVG
 1.x.</p>
 </li>

 <li>Build and install Mesa as usual.</li>
 </ol>

 <p>In the given example, it will build and install <code>libEGL</code>,
 <code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>,
 <code>libOpenVG</code>, and one or more EGL drivers.</p>

 <h3>Configure Options</h3>

 <p>There are several options that control the build of EGL at configuration
 time</p>

 <ul>
 <li><code>--enable-egl</code>

 <p>By default, EGL is enabled.  When disabled, the main library and the drivers
 will not be built.</p>

 </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-platforms</code>

 <p>List the platforms (window systems) to support.  Its argument is a comma
 seprated string such as <code>--with-egl-platforms=x11,kms</code>.  It decides
 the platforms a driver may support.  The first listed platform is also used by
 the main library to decide the native platform: the platform the EGL native
 types such as <code>EGLNativeDisplayType</code> or
 <code>EGLNativeWindowType</code> defined for.</p>

 <p>The available platforms are <code>x11</code>, <code>kms</code>,
 <code>fbdev</code>, and <code>gdi</code>.  The <code>gdi</code> platform can
 only be built with SCons.</p>

 </li>

 <li><code>--with-state-trackers</code>

 <p>The argument is a comma separated string.  It is usually used to specify the
 rendering APIs, such as OpenVG, to build.  But it is also used to specify
 <code>egl</code> state tracker that <code>egl_gallium</code> depends on.</p>

 </li>

 <li><code>--enable-gles-overlay</code>

 <p>OpenGL and OpenGL ES are not controlled by
 <code>--with-state-trackers</code>.  OpenGL is always built.  To build OpenGL
 ES, this option must be explicitly given.</p>

 </li>

 <li><code>--enable-gles1</code> and <code>--enable-gles2</code>

 <p>Unlike <code>--enable-gles-overlay</code>, which builds one library for each
 rendering API, these options enable OpenGL ES support in OpenGL.  The result is
 one big library that supports multiple APIs.</p>

 </li>

 </ul>

 <h2>Use EGL</h2>

 <h3>Demos</h3>

 <p>There are demos for the client APIs supported by EGL.  They can be found in
 mesa/demos repository.</p>

 <h3>Environment Variables</h3>

 <p>There are several environment variables that control the behavior of EGL at
 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 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>

 <li><code>EGL_PLATFORM</code>

 <p>This variable specifies the native platform.  The valid values are the same
 as those for <code>--with-egl-platforms</code>.  When the variable is not set,
 the main library uses the first platform listed in
 <code>--with-egl-platforms</code> as the native platform</p>

 </li>

 <li><code>EGL_LOG_LEVEL</code>

 <p>This changes the log level of the main library and the drivers.  The valid
 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 <code>fatal</code>.</p>

 </li>

 <li><code>EGL_SOFTWARE</code>

 <p>For drivers that support both hardware and software rendering, setting this
 variable to true forces the use of software rendering.</p>

 </li>
 </ul>

 <h2>EGL Drivers</h2>

 <ul>
 <li><code>egl_gallium</code>

 <p>This driver is based on Gallium3D.  It supports all rendering APIs and
 hardwares supported by Gallium3D.  It is the only driver that supports OpenVG.
 The supported platforms are X11, KMS, FBDEV, and GDI.</p>

 </li>

 <li><code>egl_glx</code>

 <p>This driver provides a wrapper to GLX.  It uses exclusively GLX to implement
 the EGL API.  It supports both direct and indirect rendering when the GLX does.
 It is accelerated when the GLX is.  As such, it cannot provide functions that
 is not available in GLX or GLX extensions.</p>
 </li>

 <li><code>egl_dri2</code>

 <p>This driver supports the X Window System as its window system.  It functions
 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_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>

 <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&lt;Resource&gt;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&lt;Resource&gt;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><code>EGLDisplay</code> Mutex</h3>

 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 functions (well, except for GetProcAddress which does not take an
 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 not be called with the sample display at the same time.  If a driver has access
 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 should as well lock the display before using it.

 <h3>TODOs</h3>

 <ul>
 <li>Pass the conformance tests</li>
 <li>Better automatic driver selection: <code>EGL_PLATFORM</code> loads all
 drivers and might eat too much memory.</li>

 </ul>

 </body>
 </html>
	<html>

	<title>Mesa EGL</title>

	<head><link rel="stylesheet" type="text/css" href="mesa.css"></head>

	<body>

	<h1>Mesa EGL</h1>

	<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/" 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
	API entry points and helper functions for use by the drivers. Drivers are
	dynamically loaded by the main library and most of the EGL API calls are
	directly dispatched to the drivers.</p>

	<p>The driver in use decides the window system to support. For drivers that
	support hardware rendering, there are usually multiple drivers supporting the
	same window system. Each one of of them supports a certain range of graphics
	cards.</p>

	<h2>Build EGL</h2>

	<ol>
	<li>
	<p>Run <code>configure</code> with the desired state trackers and enable
	the Gallium driver for your hardware. For example</p>

	<pre>
	$ ./configure --enable-gles-overlay --with-state-trackers=egl,vega --enable-gallium-intel
	</pre>

	<p>The main library and OpenGL is enabled by default. The first option enables
	<a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The <code>egl</code> state
	tracker is needed by a number of EGL drivers. EGL drivers will be covered
	later. The <a href="openvg.html">vega state tracker</a> provides OpenVG
	1.x.</p>
	</li>

	<li>Build and install Mesa as usual.</li>
	</ol>

	<p>In the given example, it will build and install <code>libEGL</code>,
	<code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>,
	<code>libOpenVG</code>, and one or more EGL drivers.</p>

	<h3>Configure Options</h3>

	<p>There are several options that control the build of EGL at configuration
	time</p>

	<ul>
	<li><code>--enable-egl</code>

	<p>By default, EGL is enabled. When disabled, the main library and the drivers
	will not be built.</p>

	</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-platforms</code>

	<p>List the platforms (window systems) to support. Its argument is a comma
	seprated string such as <code>--with-egl-platforms=x11,kms</code>. It decides
	the platforms a driver may support. The first listed platform is also used by
	the main library to decide the native platform: the platform the EGL native
	types such as <code>EGLNativeDisplayType</code> or
	<code>EGLNativeWindowType</code> defined for.</p>

	<p>The available platforms are <code>x11</code>, <code>kms</code>,
	<code>fbdev</code>, and <code>gdi</code>. The <code>gdi</code> platform can
	only be built with SCons.</p>

	</li>

	<li><code>--with-state-trackers</code>

	<p>The argument is a comma separated string. It is usually used to specify the
	rendering APIs, such as OpenVG, to build. But it is also used to specify
	<code>egl</code> state tracker that <code>egl_gallium</code> depends on.</p>

	</li>

	<li><code>--enable-gles-overlay</code>

	<p>OpenGL and OpenGL ES are not controlled by
	<code>--with-state-trackers</code>. OpenGL is always built. To build OpenGL
	ES, this option must be explicitly given.</p>

	</li>

	<li><code>--enable-gles1</code> and <code>--enable-gles2</code>

	<p>Unlike <code>--enable-gles-overlay</code>, which builds one library for each
	rendering API, these options enable OpenGL ES support in OpenGL. The result is
	one big library that supports multiple APIs.</p>

	</li>

	</ul>

	<h2>Use EGL</h2>

	<h3>Demos</h3>

	<p>There are demos for the client APIs supported by EGL. They can be found in
	mesa/demos repository.</p>

	<h3>Environment Variables</h3>

	<p>There are several environment variables that control the behavior of EGL at
	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 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>

	<li><code>EGL_PLATFORM</code>

	<p>This variable specifies the native platform. The valid values are the same
	as those for <code>--with-egl-platforms</code>. When the variable is not set,
	the main library uses the first platform listed in
	<code>--with-egl-platforms</code> as the native platform</p>

	</li>

	<li><code>EGL_LOG_LEVEL</code>

	<p>This changes the log level of the main library and the drivers. The valid
	values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
	<code>fatal</code>.</p>

	</li>

	<li><code>EGL_SOFTWARE</code>

	<p>For drivers that support both hardware and software rendering, setting this
	variable to true forces the use of software rendering.</p>

	</li>
	</ul>

	<h2>EGL Drivers</h2>

	<ul>
	<li><code>egl_gallium</code>

	<p>This driver is based on Gallium3D. It supports all rendering APIs and
	hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
	The supported platforms are X11, KMS, FBDEV, and GDI.</p>

	</li>

	<li><code>egl_glx</code>

	<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
	the EGL API. It supports both direct and indirect rendering when the GLX does.
	It is accelerated when the GLX is. As such, it cannot provide functions that
	is not available in GLX or GLX extensions.</p>
	</li>

	<li><code>egl_dri2</code>

	<p>This driver supports the X Window System as its window system. It functions
	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_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>

	<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><code>EGLDisplay</code> Mutex</h3>

	The <code>EGLDisplay</code> will be locked before calling any of the dispatch
	functions (well, except for GetProcAddress which does not take an
	<code>EGLDisplay</code>). This guarantees that the same dispatch function will
	not be called with the sample display at the same time. If a driver has access
	to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
	should as well lock the display before using it.

	<h3>TODOs</h3>

	<ul>
	<li>Pass the conformance tests</li>
	<li>Better automatic driver selection: <code>EGL_PLATFORM</code> loads all
	drivers and might eat too much memory.</li>

	</ul>

	</body>
	</html>