| 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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| 2 | <html lang="en">
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| 3 | <head>
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| 4 | <meta http-equiv="content-type" content="text/html; charset=utf-8">
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| 5 | <title>Mesa EGL</title>
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| 6 | <link rel="stylesheet" type="text/css" href="mesa.css">
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| 7 | </head>
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| 8 | <body>
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| 9 |
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| 10 | <div class="header">
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| 11 | <h1>The Mesa 3D Graphics Library</h1>
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| 12 | </div>
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| 13 |
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| 14 | <iframe src="contents.html"></iframe>
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| 15 | <div class="content">
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| 16 |
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| 17 | <h1>Mesa EGL</h1>
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| 18 |
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| 19 | <p>The current version of EGL in Mesa implements EGL 1.4. More information
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| 20 | about EGL can be found at
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| 21 | <a href="https://www.khronos.org/egl/">
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| 22 | https://www.khronos.org/egl/</a>.</p>
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| 23 |
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| 24 | <p>The Mesa's implementation of EGL uses a driver architecture. The main
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| 25 | library (<code>libEGL</code>) is window system neutral. It provides the EGL
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| 26 | API entry points and helper functions for use by the drivers. Drivers are
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| 27 | dynamically loaded by the main library and most of the EGL API calls are
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| 28 | directly dispatched to the drivers.</p>
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| 29 |
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| 30 | <p>The driver in use decides the window system to support.</p>
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| 31 |
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| 32 | <h2>Build EGL</h2>
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| 33 |
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| 34 | <ol>
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| 35 | <li>
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| 36 | <p>Run <code>configure</code> with the desired client APIs and enable
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| 37 | the driver for your hardware. For example</p>
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| 38 |
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| 39 | <pre>
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| 40 | $ ./configure --enable-gles1 --enable-gles2 \
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| 41 | --with-dri-drivers=... \
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| 42 | --with-gallium-drivers=...
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| 43 | </pre>
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| 44 |
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| 45 | <p>The main library and OpenGL is enabled by default. The first two options
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| 46 | above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The last two
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| 47 | options enables the listed classic and Gallium drivers respectively.</p>
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| 48 |
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| 49 | </li>
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| 50 |
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| 51 | <li>Build and install Mesa as usual.</li>
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| 52 | </ol>
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| 53 |
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| 54 | <p>In the given example, it will build and install <code>libEGL</code>,
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| 55 | <code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>, and one
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| 56 | or more EGL drivers.</p>
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| 57 |
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| 58 | <h3>Configure Options</h3>
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| 59 |
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| 60 | <p>There are several options that control the build of EGL at configuration
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| 61 | time</p>
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| 62 |
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| 63 | <dl>
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| 64 | <dt><code>--enable-egl</code></dt>
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| 65 | <dd>
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| 66 |
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| 67 | <p>By default, EGL is enabled. When disabled, the main library and the drivers
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| 68 | will not be built.</p>
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| 69 |
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| 70 | </dd>
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| 71 |
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| 72 | <dt><code>--with-egl-driver-dir</code></dt>
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| 73 | <dd>
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| 74 |
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| 75 | <p>The directory EGL drivers should be installed to. If not specified, EGL
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| 76 | drivers will be installed to <code>${libdir}/egl</code>.</p>
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| 77 |
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| 78 | </dd>
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| 79 |
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| 80 | <dt><code>--with-platforms</code></dt>
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| 81 | <dd>
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| 82 |
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| 83 | <p>List the platforms (window systems) to support. Its argument is a comma
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| 84 | separated string such as <code>--with-platforms=x11,drm</code>. It decides
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| 85 | the platforms a driver may support. The first listed platform is also used by
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| 86 | the main library to decide the native platform.</p>
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| 87 |
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| 88 | <p>The available platforms are <code>x11</code>, <code>drm</code>,
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| 89 | <code>wayland</code>, <code>surfaceless</code>, <code>android</code>,
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| 90 | and <code>haiku</code>.
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| 91 | The <code>android</code> platform can either be built as a system
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| 92 | component, part of AOSP, using <code>Android.mk</code> files, or
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| 93 | cross-compiled using appropriate <code>configure</code> options.
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| 94 | The <code>haiku</code> platform can only be built with SCons.
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| 95 | Unless for special needs, the build system should
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| 96 | select the right platforms automatically.</p>
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| 97 |
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| 98 | </dd>
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| 99 |
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| 100 | <dt><code>--enable-gles1</code></dt>
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| 101 | <dt><code>--enable-gles2</code></dt>
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| 102 | <dd>
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| 103 |
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| 104 | <p>These options enable OpenGL ES support in OpenGL. The result is one big
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| 105 | internal library that supports multiple APIs.</p>
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| 106 |
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| 107 | </dd>
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| 108 |
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| 109 | <dt><code>--enable-shared-glapi</code></dt>
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| 110 | <dd>
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| 111 |
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| 112 | <p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
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| 113 | This options makes <code>libGL</code> use the shared <code>libglapi</code>. This
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| 114 | is required if applications mix OpenGL and OpenGL ES.</p>
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| 115 |
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| 116 | </dd>
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| 117 |
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| 118 | </dl>
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| 119 |
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| 120 | <h2>Use EGL</h2>
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| 121 |
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| 122 | <h3>Demos</h3>
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| 123 |
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| 124 | <p>There are demos for the client APIs supported by EGL. They can be found in
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| 125 | mesa/demos repository.</p>
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| 126 |
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| 127 | <h3>Environment Variables</h3>
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| 128 |
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| 129 | <p>There are several environment variables that control the behavior of EGL at
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| 130 | runtime</p>
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| 131 |
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| 132 | <dl>
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| 133 | <dt><code>EGL_PLATFORM</code></dt>
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| 134 | <dd>
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| 135 |
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| 136 | <p>This variable specifies the native platform. The valid values are the same
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| 137 | as those for <code>--with-platforms</code>. When the variable is not set,
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| 138 | the main library uses the first platform listed in
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| 139 | <code>--with-platforms</code> as the native platform.</p>
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| 140 |
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| 141 | <p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
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| 142 | create displays for non-native platforms. These extensions are usually used by
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| 143 | applications that support non-native platforms. Setting this variable is
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| 144 | probably required only for some of the demos found in mesa/demo repository.</p>
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| 145 |
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| 146 | </dd>
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| 147 |
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| 148 | <dt><code>EGL_LOG_LEVEL</code></dt>
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| 149 | <dd>
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| 150 |
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| 151 | <p>This changes the log level of the main library and the drivers. The valid
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| 152 | values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
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| 153 | <code>fatal</code>.</p>
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| 154 |
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| 155 | </dd>
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| 156 | </dl>
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| 157 |
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| 158 | <h2>EGL Drivers</h2>
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| 159 |
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| 160 | <dl>
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| 161 | <dt><code>egl_dri2</code></dt>
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| 162 | <dd>
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| 163 |
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| 164 | <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
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| 165 | It functions as a DRI driver loader. For <code>x11</code> support, it talks to
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| 166 | the X server directly using (XCB-)DRI2 protocol.</p>
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| 167 |
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| 168 | <p>This driver can share DRI drivers with <code>libGL</code>.</p>
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| 169 |
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| 170 | </dd>
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| 171 |
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| 172 | <h2>Packaging</h2>
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| 173 |
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| 174 | <p>The ABI between the main library and its drivers are not stable. Nor is
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| 175 | there a plan to stabilize it at the moment.</p>
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| 176 |
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| 177 | <h2>Developers</h2>
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| 178 |
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| 179 | <p>The sources of the main library and drivers can be found at
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| 180 | <code>src/egl/</code>.</p>
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| 181 |
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| 182 | <h3>Lifetime of Display Resources</h3>
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| 183 |
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| 184 | <p>Contexts and surfaces are examples of display resources. They might live
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| 185 | longer than the display that creates them.</p>
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| 186 |
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| 187 | <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
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| 188 | display resources should be destroyed. Similarly, when a thread is released
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| 189 | through <code>eglReleaseThread</code>, all current display resources should be
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| 190 | released. Another way to destroy or release resources is through functions
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| 191 | such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
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| 192 |
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| 193 | <p>When a resource that is current to some thread is destroyed, the resource
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| 194 | should not be destroyed immediately. EGL requires the resource to live until
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| 195 | it is no longer current. A driver usually calls
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| 196 | <code>eglIs<Resource>Bound</code> to check if a resource is bound
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| 197 | (current) to any thread in the destroy callbacks. If it is still bound, the
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| 198 | resource is not destroyed.</p>
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| 199 |
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| 200 | <p>The main library will mark destroyed current resources as unlinked. In a
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| 201 | driver's <code>MakeCurrent</code> callback,
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| 202 | <code>eglIs<Resource>Linked</code> can then be called to check if a newly
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| 203 | released resource is linked to a display. If it is not, the last reference to
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| 204 | the resource is removed and the driver should destroy the resource. But it
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| 205 | should be careful here because <code>MakeCurrent</code> might be called with an
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| 206 | uninitialized display.</p>
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| 207 |
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| 208 | <p>This is the only mechanism provided by the main library to help manage the
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| 209 | resources. The drivers are responsible to the correct behavior as defined by
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| 210 | EGL.</p>
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| 211 |
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| 212 | <h3><code>EGL_RENDER_BUFFER</code></h3>
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| 213 |
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| 214 | <p>In EGL, the color buffer a context should try to render to is decided by the
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| 215 | binding surface. It should try to render to the front buffer if the binding
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| 216 | surface has <code>EGL_RENDER_BUFFER</code> set to
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| 217 | <code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
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| 218 | surface with <code>EGL_RENDER_BUFFER</code> set to
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| 219 | <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
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| 220 | buffer. However, the context is allowed to make the final decision as to which
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| 221 | color buffer it wants to or is able to render to.</p>
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| 222 |
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| 223 | <p>For pbuffer surfaces, the render buffer is always
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| 224 | <code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
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| 225 | always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
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| 226 | requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
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| 227 | result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
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| 228 | <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
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| 229 | config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
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| 230 | pbuffer surfaces.</p>
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| 231 |
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| 232 | <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
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| 233 | single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
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| 234 | is desirable that a driver allocates a private color buffer for each pbuffer
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| 235 | surface created. If the window system the driver supports has native pbuffers,
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| 236 | or if the native pixmaps have more than one color buffers, the driver should
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| 237 | carefully attach the native color buffers to the EGL surfaces, re-route them if
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| 238 | required.</p>
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| 239 |
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| 240 | <p>There is no defined behavior as to, for example, how
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| 241 | <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
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| 242 | now, it is desired that the draw buffer in a client API be fixed for pixmap and
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| 243 | pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
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| 244 | client API renders to the specified render buffer for pixmap and pbuffer
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| 245 | surfaces.</p>
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| 246 |
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| 247 | <h3><code>EGLDisplay</code> Mutex</h3>
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| 248 |
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| 249 | The <code>EGLDisplay</code> will be locked before calling any of the dispatch
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| 250 | functions (well, except for GetProcAddress which does not take an
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| 251 | <code>EGLDisplay</code>). This guarantees that the same dispatch function will
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| 252 | not be called with the sample display at the same time. If a driver has access
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| 253 | to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
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| 254 | should as well lock the display before using it.
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| 255 |
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| 256 | </div>
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| 257 | </body>
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| 258 | </html>
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