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 20 about EGL can be found at 21 <a href="http://www.khronos.org/egl/"> 22 http://www.khronos.org/egl/</a>.</p> 23 24 <p>The Mesa's implementation of EGL uses a driver architecture. The main 25 library (<code>libEGL</code>) is window system neutral. It provides the EGL 26 API entry points and helper functions for use by the drivers. Drivers are 27 dynamically loaded by the main library and most of the EGL API calls are 28 directly 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 37 the 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 46 above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The last two 47 options 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 56 or 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 61 time</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 68 will 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 76 drivers 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 84 separated string such as <code>--with-egl-platforms=x11,drm</code>. It decides 85 the platforms a driver may support. The first listed platform is also used by 86 the main library to decide the native platform: the platform the EGL native 87 types 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>, 92 and <code>haiku</code>. 93 The <code>android</code> platform can either be built as a system 94 component, part of AOSP, using <code>Android.mk</code> files, or 95 cross-compiled using appropriate <code>configure</code> options. 96 The <code>haiku</code> platform can only be built with SCons. 97 Unless for special needs, the build system should 98 select 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 107 internal 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>. 115 This options makes <code>libGL</code> use the shared <code>libglapi</code>. This 116 is 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 127 mesa/demos repository.</p> 128 129 <h3>Environment Variables</h3> 130 131 <p>There are several environment variables that control the behavior of EGL at 132 runtime</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 139 the drivers are installed to. This variable specifies a list of 140 colon-separated directories where the main library will look for drivers, in 141 addition to the default directory. This variable is ignored for setuid/setgid 142 binaries.</p> 143 144 <p>This variable is usually set to test an uninstalled build. For example, one 145 may 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 160 forces the specified EGL driver to be loaded. It comes in handy when one wants 161 to test a specific driver. This variable is ignored for setuid/setgid 162 binaries.</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 170 as those for <code>--with-egl-platforms</code>. When the variable is not set, 171 the 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 175 create displays for non-native platforms. These extensions are usually used by 176 applications that support non-native platforms. Setting this variable is 177 probably 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 185 values 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. 198 It functions as a DRI driver loader. For <code>x11</code> support, it talks to 199 the 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 208 there 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 218 longer than the display that creates them.</p> 219 220 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all 221 display resources should be destroyed. Similarly, when a thread is released 222 through <code>eglReleaseThread</code>, all current display resources should be 223 released. Another way to destroy or release resources is through functions 224 such 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 227 should not be destroyed immediately. EGL requires the resource to live until 228 it 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 231 resource is not destroyed.</p> 232 233 <p>The main library will mark destroyed current resources as unlinked. In a 234 driver's <code>MakeCurrent</code> callback, 235 <code>eglIs<Resource>Linked</code> can then be called to check if a newly 236 released resource is linked to a display. If it is not, the last reference to 237 the resource is removed and the driver should destroy the resource. But it 238 should be careful here because <code>MakeCurrent</code> might be called with an 239 uninitialized display.</p> 240 241 <p>This is the only mechanism provided by the main library to help manage the 242 resources. The drivers are responsible to the correct behavior as defined by 243 EGL.</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 248 binding surface. It should try to render to the front buffer if the binding 249 surface has <code>EGL_RENDER_BUFFER</code> set to 250 <code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a 251 surface with <code>EGL_RENDER_BUFFER</code> set to 252 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back 253 buffer. However, the context is allowed to make the final decision as to which 254 color 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 258 always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec 259 requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a 260 result, 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 262 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or 263 pbuffer surfaces.</p> 264 265 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be 266 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It 267 is desirable that a driver allocates a private color buffer for each pbuffer 268 surface created. If the window system the driver supports has native pbuffers, 269 or if the native pixmaps have more than one color buffers, the driver should 270 carefully attach the native color buffers to the EGL surfaces, re-route them if 271 required.</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 275 now, it is desired that the draw buffer in a client API be fixed for pixmap and 276 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the 277 client API renders to the specified render buffer for pixmap and pbuffer 278 surfaces.</p> 279 280 <h3><code>EGLDisplay</code> Mutex</h3> 281 282 The <code>EGLDisplay</code> will be locked before calling any of the dispatch 283 functions (well, except for GetProcAddress which does not take an 284 <code>EGLDisplay</code>). This guarantees that the same dispatch function will 285 not be called with the sample display at the same time. If a driver has access 286 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver 287 should as well lock the display before using it. 288 289 </div> 290 </body> 291 </html> 292
