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="http://www.khronos.org/egl/"> 22http://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 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-egl-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-egl-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: the platform the EGL native 87types such as <code>EGLNativeDisplayType</code> or 88<code>EGLNativeWindowType</code> defined for.</p> 89 90<p>The available platforms are <code>x11</code>, <code>drm</code>, 91<code>wayland</code>, <code>surfaceless</code>, <code>android</code>, 92and <code>haiku</code>. 93The <code>android</code> platform can either be built as a system 94component, part of AOSP, using <code>Android.mk</code> files, or 95cross-compiled using appropriate <code>configure</code> options. 96The <code>haiku</code> platform can only be built with SCons. 97Unless for special needs, the build system should 98select the right platforms automatically.</p> 99 100</dd> 101 102<dt><code>--enable-gles1</code></dt> 103<dt><code>--enable-gles2</code></dt> 104<dd> 105 106<p>These options enable OpenGL ES support in OpenGL. The result is one big 107internal library that supports multiple APIs.</p> 108 109</dd> 110 111<dt><code>--enable-shared-glapi</code></dt> 112<dd> 113 114<p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>. 115This options makes <code>libGL</code> use the shared <code>libglapi</code>. This 116is required if applications mix OpenGL and OpenGL ES.</p> 117 118</dd> 119 120</dl> 121 122<h2>Use EGL</h2> 123 124<h3>Demos</h3> 125 126<p>There are demos for the client APIs supported by EGL. They can be found in 127mesa/demos repository.</p> 128 129<h3>Environment Variables</h3> 130 131<p>There are several environment variables that control the behavior of EGL at 132runtime</p> 133 134<dl> 135<dt><code>EGL_DRIVERS_PATH</code></dt> 136<dd> 137 138<p>By default, the main library will look for drivers in the directory where 139the drivers are installed to. This variable specifies a list of 140colon-separated directories where the main library will look for drivers, in 141addition to the default directory. This variable is ignored for setuid/setgid 142binaries.</p> 143 144<p>This variable is usually set to test an uninstalled build. For example, one 145may set</p> 146 147<pre> 148 $ export LD_LIBRARY_PATH=$mesa/lib 149 $ export EGL_DRIVERS_PATH=$mesa/lib/egl 150</pre> 151 152<p>to test a build without installation</p> 153 154</dd> 155 156<dt><code>EGL_DRIVER</code></dt> 157<dd> 158 159<p>This variable specifies a full path to or the name of an EGL driver. It 160forces the specified EGL driver to be loaded. It comes in handy when one wants 161to test a specific driver. This variable is ignored for setuid/setgid 162binaries.</p> 163 164</dd> 165 166<dt><code>EGL_PLATFORM</code></dt> 167<dd> 168 169<p>This variable specifies the native platform. The valid values are the same 170as those for <code>--with-egl-platforms</code>. When the variable is not set, 171the main library uses the first platform listed in 172<code>--with-egl-platforms</code> as the native platform.</p> 173 174<p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to 175create displays for non-native platforms. These extensions are usually used by 176applications that support non-native platforms. Setting this variable is 177probably required only for some of the demos found in mesa/demo repository.</p> 178 179</dd> 180 181<dt><code>EGL_LOG_LEVEL</code></dt> 182<dd> 183 184<p>This changes the log level of the main library and the drivers. The valid 185values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and 186<code>fatal</code>.</p> 187 188</dd> 189</dl> 190 191<h2>EGL Drivers</h2> 192 193<dl> 194<dt><code>egl_dri2</code></dt> 195<dd> 196 197<p>This driver supports both <code>x11</code> and <code>drm</code> platforms. 198It functions as a DRI driver loader. For <code>x11</code> support, it talks to 199the X server directly using (XCB-)DRI2 protocol.</p> 200 201<p>This driver can share DRI drivers with <code>libGL</code>.</p> 202 203</dd> 204 205<h2>Packaging</h2> 206 207<p>The ABI between the main library and its drivers are not stable. Nor is 208there a plan to stabilize it at the moment.</p> 209 210<h2>Developers</h2> 211 212<p>The sources of the main library and drivers can be found at 213<code>src/egl/</code>.</p> 214 215<h3>Lifetime of Display Resources</h3> 216 217<p>Contexts and surfaces are examples of display resources. They might live 218longer than the display that creates them.</p> 219 220<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all 221display resources should be destroyed. Similarly, when a thread is released 222through <code>eglReleaseThread</code>, all current display resources should be 223released. Another way to destroy or release resources is through functions 224such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p> 225 226<p>When a resource that is current to some thread is destroyed, the resource 227should not be destroyed immediately. EGL requires the resource to live until 228it is no longer current. A driver usually calls 229<code>eglIs<Resource>Bound</code> to check if a resource is bound 230(current) to any thread in the destroy callbacks. If it is still bound, the 231resource is not destroyed.</p> 232 233<p>The main library will mark destroyed current resources as unlinked. In a 234driver's <code>MakeCurrent</code> callback, 235<code>eglIs<Resource>Linked</code> can then be called to check if a newly 236released resource is linked to a display. If it is not, the last reference to 237the resource is removed and the driver should destroy the resource. But it 238should be careful here because <code>MakeCurrent</code> might be called with an 239uninitialized display.</p> 240 241<p>This is the only mechanism provided by the main library to help manage the 242resources. The drivers are responsible to the correct behavior as defined by 243EGL.</p> 244 245<h3><code>EGL_RENDER_BUFFER</code></h3> 246 247<p>In EGL, the color buffer a context should try to render to is decided by the 248binding surface. It should try to render to the front buffer if the binding 249surface has <code>EGL_RENDER_BUFFER</code> set to 250<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a 251surface with <code>EGL_RENDER_BUFFER</code> set to 252<code>EGL_BACK_BUFFER</code>, the context should try to render to the back 253buffer. However, the context is allowed to make the final decision as to which 254color buffer it wants to or is able to render to.</p> 255 256<p>For pbuffer surfaces, the render buffer is always 257<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is 258always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec 259requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a 260result, a driver should never set <code>EGL_PIXMAP_BIT</code> or 261<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the 262config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or 263pbuffer surfaces.</p> 264 265<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be 266single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It 267is desirable that a driver allocates a private color buffer for each pbuffer 268surface created. If the window system the driver supports has native pbuffers, 269or if the native pixmaps have more than one color buffers, the driver should 270carefully attach the native color buffers to the EGL surfaces, re-route them if 271required.</p> 272 273<p>There is no defined behavior as to, for example, how 274<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right 275now, it is desired that the draw buffer in a client API be fixed for pixmap and 276pbuffer surfaces. Therefore, the driver is responsible to guarantee that the 277client API renders to the specified render buffer for pixmap and pbuffer 278surfaces.</p> 279 280<h3><code>EGLDisplay</code> Mutex</h3> 281 282The <code>EGLDisplay</code> will be locked before calling any of the dispatch 283functions (well, except for GetProcAddress which does not take an 284<code>EGLDisplay</code>). This guarantees that the same dispatch function will 285not be called with the sample display at the same time. If a driver has access 286to an <code>EGLDisplay</code> without going through the EGL APIs, the driver 287should as well lock the display before using it. 288 289</div> 290</body> 291</html> 292