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="https://www.khronos.org/egl/"> 22 https://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 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-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-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.</p> 87 88 <p>The available platforms are <code>x11</code>, <code>drm</code>, 89 <code>wayland</code>, <code>surfaceless</code>, <code>android</code>, 90 and <code>haiku</code>. 91 The <code>android</code> platform can either be built as a system 92 component, part of AOSP, using <code>Android.mk</code> files, or 93 cross-compiled using appropriate <code>configure</code> options. 94 The <code>haiku</code> platform can only be built with SCons. 95 Unless for special needs, the build system should 96 select 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 105 internal 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>. 113 This options makes <code>libGL</code> use the shared <code>libglapi</code>. This 114 is 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 125 mesa/demos repository.</p> 126 127 <h3>Environment Variables</h3> 128 129 <p>There are several environment variables that control the behavior of EGL at 130 runtime</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 137 as those for <code>--with-platforms</code>. When the variable is not set, 138 the 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 142 create displays for non-native platforms. These extensions are usually used by 143 applications that support non-native platforms. Setting this variable is 144 probably 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 152 values 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. 165 It functions as a DRI driver loader. For <code>x11</code> support, it talks to 166 the 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 175 there 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 185 longer than the display that creates them.</p> 186 187 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all 188 display resources should be destroyed. Similarly, when a thread is released 189 through <code>eglReleaseThread</code>, all current display resources should be 190 released. Another way to destroy or release resources is through functions 191 such 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 194 should not be destroyed immediately. EGL requires the resource to live until 195 it 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 198 resource is not destroyed.</p> 199 200 <p>The main library will mark destroyed current resources as unlinked. In a 201 driver's <code>MakeCurrent</code> callback, 202 <code>eglIs<Resource>Linked</code> can then be called to check if a newly 203 released resource is linked to a display. If it is not, the last reference to 204 the resource is removed and the driver should destroy the resource. But it 205 should be careful here because <code>MakeCurrent</code> might be called with an 206 uninitialized display.</p> 207 208 <p>This is the only mechanism provided by the main library to help manage the 209 resources. The drivers are responsible to the correct behavior as defined by 210 EGL.</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 215 binding surface. It should try to render to the front buffer if the binding 216 surface has <code>EGL_RENDER_BUFFER</code> set to 217 <code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a 218 surface with <code>EGL_RENDER_BUFFER</code> set to 219 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back 220 buffer. However, the context is allowed to make the final decision as to which 221 color 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 225 always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec 226 requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a 227 result, 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 229 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or 230 pbuffer surfaces.</p> 231 232 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be 233 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It 234 is desirable that a driver allocates a private color buffer for each pbuffer 235 surface created. If the window system the driver supports has native pbuffers, 236 or if the native pixmaps have more than one color buffers, the driver should 237 carefully attach the native color buffers to the EGL surfaces, re-route them if 238 required.</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 242 now, it is desired that the draw buffer in a client API be fixed for pixmap and 243 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the 244 client API renders to the specified render buffer for pixmap and pbuffer 245 surfaces.</p> 246 247 <h3><code>EGLDisplay</code> Mutex</h3> 248 249 The <code>EGLDisplay</code> will be locked before calling any of the dispatch 250 functions (well, except for GetProcAddress which does not take an 251 <code>EGLDisplay</code>). This guarantees that the same dispatch function will 252 not be called with the sample display at the same time. If a driver has access 253 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver 254 should as well lock the display before using it. 255 256 </div> 257 </body> 258 </html> 259
