Erik Faye-Lund
ecdab0dfea
It's generally frowned upon to have more than one H1 per document in HTML4. So let's put the text directly inside the header. This means we can drop the flex-based centering, which makes things a bit easier. We also need to change the padding to rem instead of em, because the em has now changed. Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com> Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
255 lines
8.9 KiB
HTML
255 lines
8.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html lang="en">
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<head>
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<meta http-equiv="content-type" content="text/html; charset=utf-8">
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<title>EGL</title>
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<link rel="stylesheet" type="text/css" href="mesa.css">
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</head>
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<body>
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<div class="header">
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The Mesa 3D Graphics Library
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</div>
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<iframe src="contents.html"></iframe>
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<div class="content">
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<h1>EGL</h1>
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<p>The current version of EGL in Mesa implements EGL 1.4. More information
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about EGL can be found at
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<a href="https://www.khronos.org/egl/">
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https://www.khronos.org/egl/</a>.</p>
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<p>The Mesa's implementation of EGL uses a driver architecture. The main
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library (<code>libEGL</code>) is window system neutral. It provides the EGL
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API entry points and helper functions for use by the drivers. Drivers are
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dynamically loaded by the main library and most of the EGL API calls are
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directly dispatched to the drivers.</p>
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<p>The driver in use decides the window system to support.</p>
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<h2>Build EGL</h2>
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<ol>
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<li>
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<p>Configure your build with the desired client APIs and enable
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the driver for your hardware. For example:</p>
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<pre>
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$ meson configure \
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-D egl=true \
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-D gles1=true \
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-D gles2=true \
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-D dri-drivers=... \
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-D gallium-drivers=...
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</pre>
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<p>The main library and OpenGL is enabled by default. The first two options
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above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The last two
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options enables the listed classic and Gallium drivers respectively.</p>
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</li>
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<li>Build and install Mesa as usual.</li>
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</ol>
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<p>In the given example, it will build and install <code>libEGL</code>,
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<code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>, and one
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or more EGL drivers.</p>
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<h3>Configure Options</h3>
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<p>There are several options that control the build of EGL at configuration
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time</p>
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<dl>
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<dt><code>-D egl=true</code></dt>
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<dd>
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<p>By default, EGL is enabled. When disabled, the main library and the drivers
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will not be built.</p>
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</dd>
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<dt><code>-D platforms=...</code></dt>
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<dd>
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<p>List the platforms (window systems) to support. Its argument is a comma
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separated string such as <code>-D platforms=x11,drm</code>. It decides
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the platforms a driver may support. The first listed platform is also used by
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the main library to decide the native platform.</p>
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<p>The available platforms are <code>x11</code>, <code>drm</code>,
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<code>wayland</code>, <code>surfaceless</code>, <code>android</code>,
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and <code>haiku</code>.
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The <code>android</code> platform can either be built as a system
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component, part of AOSP, using <code>Android.mk</code> files, or
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cross-compiled using appropriate options.
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The <code>haiku</code> platform can only be built with SCons or Meson.
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Unless for special needs, the build system should
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select the right platforms automatically.</p>
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</dd>
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<dt><code>-D gles1=true</code></dt>
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<dt><code>-D gles2=true</code></dt>
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<dd>
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<p>These options enable OpenGL ES support in OpenGL. The result is one big
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internal library that supports multiple APIs.</p>
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</dd>
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<dt><code>-D shared-glapi=true</code></dt>
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<dd>
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<p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
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This options makes <code>libGL</code> use the shared <code>libglapi</code>. This
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is required if applications mix OpenGL and OpenGL ES.</p>
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</dd>
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</dl>
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<h2>Use EGL</h2>
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<h3>Demos</h3>
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<p>There are demos for the client APIs supported by EGL. They can be found in
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mesa/demos repository.</p>
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<h3>Environment Variables</h3>
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<p>There are several environment variables that control the behavior of EGL at
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runtime</p>
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<dl>
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<dt><code>EGL_PLATFORM</code></dt>
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<dd>
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<p>This variable specifies the native platform. The valid values are the same
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as those for <code>-D platforms=...</code>. When the variable is not set,
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the main library uses the first platform listed in
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<code>-D platforms=...</code> as the native platform.</p>
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<p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
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create displays for non-native platforms. These extensions are usually used by
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applications that support non-native platforms. Setting this variable is
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probably required only for some of the demos found in mesa/demo repository.</p>
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</dd>
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<dt><code>EGL_LOG_LEVEL</code></dt>
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<dd>
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<p>This changes the log level of the main library and the drivers. The valid
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values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
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<code>fatal</code>.</p>
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</dd>
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</dl>
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<h2>EGL Drivers</h2>
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<dl>
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<dt><code>egl_dri2</code></dt>
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<dd>
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<p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
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It functions as a DRI driver loader. For <code>x11</code> support, it talks to
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the X server directly using (XCB-)DRI2 protocol.</p>
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<p>This driver can share DRI drivers with <code>libGL</code>.</p>
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</dd>
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</dl>
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<h2>Packaging</h2>
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<p>The ABI between the main library and its drivers are not stable. Nor is
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there a plan to stabilize it at the moment.</p>
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<h2>Developers</h2>
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<p>The sources of the main library and drivers can be found at
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<code>src/egl/</code>.</p>
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<h3>Lifetime of Display Resources</h3>
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<p>Contexts and surfaces are examples of display resources. They might live
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longer than the display that creates them.</p>
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<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
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display resources should be destroyed. Similarly, when a thread is released
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through <code>eglReleaseThread</code>, all current display resources should be
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released. Another way to destroy or release resources is through functions
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such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
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<p>When a resource that is current to some thread is destroyed, the resource
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should not be destroyed immediately. EGL requires the resource to live until
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it is no longer current. A driver usually calls
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<code>eglIs<Resource>Bound</code> to check if a resource is bound
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(current) to any thread in the destroy callbacks. If it is still bound, the
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resource is not destroyed.</p>
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<p>The main library will mark destroyed current resources as unlinked. In a
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driver's <code>MakeCurrent</code> callback,
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<code>eglIs<Resource>Linked</code> can then be called to check if a newly
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released resource is linked to a display. If it is not, the last reference to
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the resource is removed and the driver should destroy the resource. But it
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should be careful here because <code>MakeCurrent</code> might be called with an
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uninitialized display.</p>
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<p>This is the only mechanism provided by the main library to help manage the
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resources. The drivers are responsible to the correct behavior as defined by
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EGL.</p>
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<h3><code>EGL_RENDER_BUFFER</code></h3>
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<p>In EGL, the color buffer a context should try to render to is decided by the
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binding surface. It should try to render to the front buffer if the binding
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surface has <code>EGL_RENDER_BUFFER</code> set to
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<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
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surface with <code>EGL_RENDER_BUFFER</code> set to
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<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
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buffer. However, the context is allowed to make the final decision as to which
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color buffer it wants to or is able to render to.</p>
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<p>For pbuffer surfaces, the render buffer is always
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<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
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always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
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requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
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result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
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<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
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config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
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pbuffer surfaces.</p>
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<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
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single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
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is desirable that a driver allocates a private color buffer for each pbuffer
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surface created. If the window system the driver supports has native pbuffers,
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or if the native pixmaps have more than one color buffers, the driver should
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carefully attach the native color buffers to the EGL surfaces, re-route them if
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required.</p>
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<p>There is no defined behavior as to, for example, how
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<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
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now, it is desired that the draw buffer in a client API be fixed for pixmap and
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pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
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client API renders to the specified render buffer for pixmap and pbuffer
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surfaces.</p>
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<h3><code>EGLDisplay</code> Mutex</h3>
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The <code>EGLDisplay</code> will be locked before calling any of the dispatch
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functions (well, except for GetProcAddress which does not take an
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<code>EGLDisplay</code>). This guarantees that the same dispatch function will
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not be called with the sample display at the same time. If a driver has access
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to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
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should as well lock the display before using it.
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</div>
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</body>
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</html>
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