1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html lang="en"> 3<head> 4 <meta http-equiv="content-type" content="text/html; charset=utf-8"> 5 <title>Mesa EGL</title> 6 <link rel="stylesheet" type="text/css" href="mesa.css"> 7</head> 8<body> 9 10<div class="header"> 11 <h1>The Mesa 3D Graphics Library</h1> 12</div> 13 14<iframe src="contents.html"></iframe> 15<div class="content"> 16 17<h1>Mesa EGL</h1> 18 19<p>The current version of EGL in Mesa implements EGL 1.4. More information 20about EGL can be found at 21<a href="https://www.khronos.org/egl/"> 22https://www.khronos.org/egl/</a>.</p> 23 24<p>The Mesa's implementation of EGL uses a driver architecture. The main 25library (<code>libEGL</code>) is window system neutral. It provides the EGL 26API entry points and helper functions for use by the drivers. Drivers are 27dynamically loaded by the main library and most of the EGL API calls are 28directly dispatched to the drivers.</p> 29 30<p>The driver in use decides the window system to support.</p> 31 32<h2>Build EGL</h2> 33 34<ol> 35<li> 36<p>Run <code>configure</code> with the desired client APIs and enable 37the driver for your hardware. For example</p> 38 39<pre> 40 $ ./configure --enable-gles1 --enable-gles2 \ 41 --with-dri-drivers=... \ 42 --with-gallium-drivers=... 43</pre> 44 45<p>The main library and OpenGL is enabled by default. The first two options 46above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The last two 47options enables the listed classic and Gallium drivers respectively.</p> 48 49</li> 50 51<li>Build and install Mesa as usual.</li> 52</ol> 53 54<p>In the given example, it will build and install <code>libEGL</code>, 55<code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>, and one 56or more EGL drivers.</p> 57 58<h3>Configure Options</h3> 59 60<p>There are several options that control the build of EGL at configuration 61time</p> 62 63<dl> 64<dt><code>--enable-egl</code></dt> 65<dd> 66 67<p>By default, EGL is enabled. When disabled, the main library and the drivers 68will not be built.</p> 69 70</dd> 71 72<dt><code>--with-egl-driver-dir</code></dt> 73<dd> 74 75<p>The directory EGL drivers should be installed to. If not specified, EGL 76drivers will be installed to <code>${libdir}/egl</code>.</p> 77 78</dd> 79 80<dt><code>--with-platforms</code></dt> 81<dd> 82 83<p>List the platforms (window systems) to support. Its argument is a comma 84separated string such as <code>--with-platforms=x11,drm</code>. It decides 85the platforms a driver may support. The first listed platform is also used by 86the main library to decide the native platform.</p> 87 88<p>The available platforms are <code>x11</code>, <code>drm</code>, 89<code>wayland</code>, <code>surfaceless</code>, <code>android</code>, 90and <code>haiku</code>. 91The <code>android</code> platform can either be built as a system 92component, part of AOSP, using <code>Android.mk</code> files, or 93cross-compiled using appropriate <code>configure</code> options. 94The <code>haiku</code> platform can only be built with SCons. 95Unless for special needs, the build system should 96select the right platforms automatically.</p> 97 98</dd> 99 100<dt><code>--enable-gles1</code></dt> 101<dt><code>--enable-gles2</code></dt> 102<dd> 103 104<p>These options enable OpenGL ES support in OpenGL. The result is one big 105internal library that supports multiple APIs.</p> 106 107</dd> 108 109<dt><code>--enable-shared-glapi</code></dt> 110<dd> 111 112<p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>. 113This options makes <code>libGL</code> use the shared <code>libglapi</code>. This 114is required if applications mix OpenGL and OpenGL ES.</p> 115 116</dd> 117 118</dl> 119 120<h2>Use EGL</h2> 121 122<h3>Demos</h3> 123 124<p>There are demos for the client APIs supported by EGL. They can be found in 125mesa/demos repository.</p> 126 127<h3>Environment Variables</h3> 128 129<p>There are several environment variables that control the behavior of EGL at 130runtime</p> 131 132<dl> 133<dt><code>EGL_PLATFORM</code></dt> 134<dd> 135 136<p>This variable specifies the native platform. The valid values are the same 137as those for <code>--with-platforms</code>. When the variable is not set, 138the main library uses the first platform listed in 139<code>--with-platforms</code> as the native platform.</p> 140 141<p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to 142create displays for non-native platforms. These extensions are usually used by 143applications that support non-native platforms. Setting this variable is 144probably required only for some of the demos found in mesa/demo repository.</p> 145 146</dd> 147 148<dt><code>EGL_LOG_LEVEL</code></dt> 149<dd> 150 151<p>This changes the log level of the main library and the drivers. The valid 152values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and 153<code>fatal</code>.</p> 154 155</dd> 156</dl> 157 158<h2>EGL Drivers</h2> 159 160<dl> 161<dt><code>egl_dri2</code></dt> 162<dd> 163 164<p>This driver supports both <code>x11</code> and <code>drm</code> platforms. 165It functions as a DRI driver loader. For <code>x11</code> support, it talks to 166the X server directly using (XCB-)DRI2 protocol.</p> 167 168<p>This driver can share DRI drivers with <code>libGL</code>.</p> 169 170</dd> 171 172<h2>Packaging</h2> 173 174<p>The ABI between the main library and its drivers are not stable. Nor is 175there a plan to stabilize it at the moment.</p> 176 177<h2>Developers</h2> 178 179<p>The sources of the main library and drivers can be found at 180<code>src/egl/</code>.</p> 181 182<h3>Lifetime of Display Resources</h3> 183 184<p>Contexts and surfaces are examples of display resources. They might live 185longer than the display that creates them.</p> 186 187<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all 188display resources should be destroyed. Similarly, when a thread is released 189through <code>eglReleaseThread</code>, all current display resources should be 190released. Another way to destroy or release resources is through functions 191such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p> 192 193<p>When a resource that is current to some thread is destroyed, the resource 194should not be destroyed immediately. EGL requires the resource to live until 195it is no longer current. A driver usually calls 196<code>eglIs<Resource>Bound</code> to check if a resource is bound 197(current) to any thread in the destroy callbacks. If it is still bound, the 198resource is not destroyed.</p> 199 200<p>The main library will mark destroyed current resources as unlinked. In a 201driver's <code>MakeCurrent</code> callback, 202<code>eglIs<Resource>Linked</code> can then be called to check if a newly 203released resource is linked to a display. If it is not, the last reference to 204the resource is removed and the driver should destroy the resource. But it 205should be careful here because <code>MakeCurrent</code> might be called with an 206uninitialized display.</p> 207 208<p>This is the only mechanism provided by the main library to help manage the 209resources. The drivers are responsible to the correct behavior as defined by 210EGL.</p> 211 212<h3><code>EGL_RENDER_BUFFER</code></h3> 213 214<p>In EGL, the color buffer a context should try to render to is decided by the 215binding surface. It should try to render to the front buffer if the binding 216surface has <code>EGL_RENDER_BUFFER</code> set to 217<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a 218surface with <code>EGL_RENDER_BUFFER</code> set to 219<code>EGL_BACK_BUFFER</code>, the context should try to render to the back 220buffer. However, the context is allowed to make the final decision as to which 221color buffer it wants to or is able to render to.</p> 222 223<p>For pbuffer surfaces, the render buffer is always 224<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is 225always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec 226requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a 227result, a driver should never set <code>EGL_PIXMAP_BIT</code> or 228<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the 229config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or 230pbuffer surfaces.</p> 231 232<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be 233single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It 234is desirable that a driver allocates a private color buffer for each pbuffer 235surface created. If the window system the driver supports has native pbuffers, 236or if the native pixmaps have more than one color buffers, the driver should 237carefully attach the native color buffers to the EGL surfaces, re-route them if 238required.</p> 239 240<p>There is no defined behavior as to, for example, how 241<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right 242now, it is desired that the draw buffer in a client API be fixed for pixmap and 243pbuffer surfaces. Therefore, the driver is responsible to guarantee that the 244client API renders to the specified render buffer for pixmap and pbuffer 245surfaces.</p> 246 247<h3><code>EGLDisplay</code> Mutex</h3> 248 249The <code>EGLDisplay</code> will be locked before calling any of the dispatch 250functions (well, except for GetProcAddress which does not take an 251<code>EGLDisplay</code>). This guarantees that the same dispatch function will 252not be called with the sample display at the same time. If a driver has access 253to an <code>EGLDisplay</code> without going through the EGL APIs, the driver 254should as well lock the display before using it. 255 256</div> 257</body> 258</html> 259