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1<html> 2 3<title>Mesa EGL</title> 4 5<head><link rel="stylesheet" type="text/css" href="mesa.css"></head> 6 7<body> 8 9<h1>Mesa EGL</h1> 10 11<p>The current version of EGL in Mesa implements EGL 1.4. More information 12about EGL can be found at 13<a href="http://www.khronos.org/egl/" target="_parent"> 14http://www.khronos.org/egl/</a>.</p> 15 16<p>The Mesa's implementation of EGL uses a driver architecture. The main 17library (<code>libEGL</code>) is window system neutral. It provides the EGL 18API entry points and helper functions for use by the drivers. Drivers are 19dynamically loaded by the main library and most of the EGL API calls are 20directly dispatched to the drivers.</p> 21 22<p>The driver in use decides the window system to support. For drivers that 23support hardware rendering, there are usually multiple drivers supporting the 24same window system. Each one of of them supports a certain range of graphics 25cards.</p> 26 27<h2>Build EGL</h2> 28 29<ol> 30<li> 31<p>Run <code>configure</code> with the desired state trackers and enable 32the Gallium driver for your hardware. For example</p> 33 34<pre> 35 $ /configure --enable-gles-overlay --with-state-trackers=egl,vega --enable-gallium-{swrast,intel} 36</pre> 37 38<p>The main library and OpenGL is enabled by default. The first option enables 39<a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The <code>egl</code> state 40tracker is needed by a number of EGL drivers. EGL drivers will be covered 41later. The <a href="openvg.html">vega state tracker</a> provides OpenVG 421.x.</p> 43</li> 44 45<li>Build and install Mesa as usual.</li> 46</ol> 47 48<p>In the given example, it will build and install <code>libEGL</code>, 49<code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>, 50<code>libOpenVG</code>, and one or more EGL drivers.</p> 51 52<h3>Configure Options</h3> 53 54<p>There are several options that control the build of EGL at configuration 55time</p> 56 57<ul> 58<li><code>--enable-egl</code> 59 60<p>By default, EGL is enabled. When disabled, the main library and the drivers 61will not be built.</p> 62 63</li> 64 65<li><code>--with-egl-driver-dir</code> 66 67<p>The directory EGL drivers should be installed to. If not specified, EGL 68drivers will be installed to <code>${libdir}/egl</code>.</p> 69 70</li> 71 72<li><code>--with-egl-displays</code> 73 74<p>List the window system(s) to support. It is by default <code>x11</code>, 75which supports the X Window System. Its argument is a comma separated string 76like, for example, <code>--with-egl-displays=x11,kms</code>. Because an EGL 77driver decides which window system to support, this example will enable two 78(sets of) EGL drivers. One supports the X window system and the other supports 79bare KMS (kernel modesetting).</p> 80 81</li> 82 83<li><code>--with-state-trackers</code> 84 85<p>The argument is a comma separated string. It is usually used to specify the 86rendering APIs, such as OpenVG, to build. But it should be noted that a number 87of EGL drivers depend on the <code>egl</code> state tracker. They will 88<em>not</em> be built without the <code>egl</code> state tracker.</p> 89 90</li> 91 92<li><code>--enable-gles-overlay</code> 93 94<p>OpenGL and OpenGL ES are not controlled by 95<code>--with-state-trackers</code>. OpenGL is always built. To build OpenGL 96ES, this option must be explicitly given.</p> 97 98</li> 99 100<li><code>--enable-gles1</code> and <code>--enable-gles2</code> 101 102<p>Unlike <code>--enable-gles-overlay</code>, which builds one library for each 103rendering API, these options enable OpenGL ES support in OpenGL. The result is 104one big library that supports multiple APIs. This is used by DRI drivers and 105<code>egl_dri2</code> EGL driver. 106 107</li> 108 109<li><code>--enable-gallium-swrast</code> 110 111<p>This option is not specific to EGL. But if there is no driver for your 112hardware, or you are experiencing problems with the hardware driver, you can 113enable the swrast DRM driver. It is a dummy driver and EGL will fallback to 114software rendering automatically.</p> 115 116</li> 117</ul> 118 119<h2>Use EGL</h2> 120 121<p>There are demos for the client APIs supported by EGL. They can be found in 122<code>progs/egl/</code>, You can use them to test your build. For example,</p> 123 124<pre> 125 $ cd progs/egl/eglut 126 $ make 127 $ cd /opengles1 128 $ make 129 $ /torus_x11 130</pre> 131 132<h3>Environment Variables</h3> 133 134<p>There are several environment variables that control the behavior of EGL at 135runtime</p> 136 137<ul> 138<li><code>EGL_DRIVERS_PATH</code> 139 140<p>By default, the main library will look for drivers in the directory where 141the drivers are installed to. This variable specifies a list of 142colon-separated directories where the main library will look for drivers, in 143addition to the default directory. This variable is ignored for setuid/setgid 144binaries.</p> 145 146</li> 147 148<li><code>EGL_DRIVER</code> 149 150<p>This variable specifies a full path to an EGL driver and it forces the 151specified EGL driver to be loaded. It comes in handy when one wants to test a 152specific driver. This variable is ignored for setuid/setgid binaries.</p> 153 154</li> 155 156<li><code>EGL_DISPLAY</code> 157 158<p>When <code>EGL_DRIVER</code> is not set, the main library loads <em>all</em> 159EGL drivers that support a certain window system. <code>EGL_DISPLAY</code> can 160be used to specify the window system and the valid values are, for example, 161<code>x11</code> or <code>kms</code>. When the variable is not set, the main 162library defaults the value to the first window system listed in 163<code>--with-egl-displays</code> at configuration time. 164 165</li> 166 167<li><code>EGL_LOG_LEVEL</code> 168 169<p>This changes the log level of the main library and the drivers. The valid 170values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and 171<code>fatal</code>.</p> 172 173</li> 174 175<li><code>EGL_SOFTWARE</code> 176 177<p>For drivers that support both hardware and software rendering, setting this 178variable to true forces the use of software rendering.</p> 179 180</li> 181</ul> 182 183<h2>EGL Drivers</h2> 184 185<p>There are two categories of EGL drivers: Gallium and classic.</p> 186 187<p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4. The 188support for optional EGL functions and EGL extensions is usually more complete 189than the classic ones. These drivers depend on the <code>egl</code> state 190tracker to build. The available drivers are</p> 191 192<ul> 193<li><code>egl_<dpy>_i915</code></li> 194<li><code>egl_<dpy>_i965</code></li> 195<li><code>egl_<dpy>_radeon</code></li> 196<li><code>egl_<dpy>_nouveau</code></li> 197<li><code>egl_<dpy>_swrast</code></li> 198<li><code>egl_<dpy>_vmwgfx</code></li> 199</ul> 200 201<p><code><dpy></code> is given by <code>--with-egl-displays</code> at 202configuration time. There will be one EGL driver for each combination of the 203displays listed and the hardware drivers enabled.</p> 204 205<p>Classic EGL drivers, on the other hand, supports only OpenGL as its 206rendering API. They can be found under <code>src/egl/drivers/</code>. There 207are 3 of them</p> 208 209<ul> 210<li><code>egl_glx</code> 211 212<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement 213the EGL API. It supports both direct and indirect rendering when the GLX does. 214It is accelerated when the GLX is. As such, it cannot provide functions that 215is not available in GLX or GLX extensions.</p> 216</li> 217 218<li><code>egl_dri2</code> 219 220<p>This driver supports the X Window System as its window system. It functions 221as a DRI2 driver loader. Unlike <code>egl_glx</code>, it has no dependency on 222<code>libGL</code>. It talks to the X server directly using DRI2 protocol.</p> 223 224</li> 225<li><code>egl_dri</code> 226 227<p>This driver lacks maintenance and does <em>not</em> build. It is similiar 228to <code>egl_dri2</code> in that it functions as a DRI(1) driver loader. But 229unlike <code>egl_dri2</code>, it supports Linux framebuffer devices as its 230window system and supports EGL_MESA_screen_surface extension. As DRI1 drivers 231are phasing out, it might eventually be replaced by <code>egl_dri2</code>.</p> 232 233</li> 234</ul> 235 236<p>To use the classic drivers, one must manually set <code>EGL_DRIVER</code> at 237runtime.</p> 238 239<h2>Developers</h2> 240 241<p>The sources of the main library and the classic drivers can be found at 242<code>src/egl/</code>. The sources of the <code>egl</code> state tracker can 243be found at <code>src/gallium/state_trackers/egl/</code>.</p> 244 245<p>The suggested way to learn to write a EGL driver is to see how other drivers 246are written. <code>egl_glx</code> should be a good reference. It works in any 247environment that has GLX support, and it is simpler than most drivers.</p> 248 249<h3>Lifetime of Display Resources</h3> 250 251<p>Contexts and surfaces are examples of display resources. They might live 252longer than the display that creates them.</p> 253 254<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all 255display resources should be destroyed. Similarly, when a thread is released 256throught <code>eglReleaseThread</code>, all current display resources should be 257released. Another way to destory or release resources is through functions 258such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p> 259 260<p>When a resource that is current to some thread is destroyed, the resource 261should not be destroyed immediately. EGL requires the resource to live until 262it is no longer current. A driver usually calls 263<code>eglIs<Resource>Bound</code> to check if a resource is bound 264(current) to any thread in the destroy callbacks. If it is still bound, the 265resource is not destroyed.</p> 266 267<p>The main library will mark destroyed current resources as unlinked. In a 268driver's <code>MakeCurrent</code> callback, 269<code>eglIs<Resource>Linked</code> can then be called to check if a newly 270released resource is linked to a display. If it is not, the last reference to 271the resource is removed and the driver should destroy the resource. But it 272should be careful here because <code>MakeCurrent</code> might be called with an 273uninitialized display.</p> 274 275<p>This is the only mechanism provided by the main library to help manage the 276resources. The drivers are responsible to the correct behavior as defined by 277EGL.</p> 278 279<h3><code>EGL_RENDER_BUFFER</code></h3> 280 281<p>In EGL, the color buffer a context should try to render to is decided by the 282binding surface. It should try to render to the front buffer if the binding 283surface has <code>EGL_RENDER_BUFFER</code> set to 284<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a 285surface with <code>EGL_RENDER_BUFFER</code> set to 286<code>EGL_BACK_BUFFER</code>, the context should try to render to the back 287buffer. However, the context is allowed to make the final decision as to which 288color buffer it wants to or is able to render to.</p> 289 290<p>For pbuffer surfaces, the render buffer is always 291<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is 292always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec 293requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a 294result, a driver should never set <code>EGL_PIXMAP_BIT</code> or 295<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the 296config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or 297pbuffer surfaces.</p> 298 299<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be 300single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It 301is desirable that a driver allocates a private color buffer for each pbuffer 302surface created. If the window system the driver supports has native pbuffers, 303or if the native pixmaps have more than one color buffers, the driver should 304carefully attach the native color buffers to the EGL surfaces, re-route them if 305required.</p> 306 307<p>There is no defined behavior as to, for example, how 308<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right 309now, it is desired that the draw buffer in a client API be fixed for pixmap and 310pbuffer surfaces. Therefore, the driver is responsible to guarantee that the 311client API renders to the specified render buffer for pixmap and pbuffer 312surfaces.</p> 313 314<h3><code>EGLDisplay</code> Mutex</h3> 315 316The <code>EGLDisplay</code> will be locked before calling any of the dispatch 317functions (well, except for GetProcAddress which does not take an 318<code>EGLDisplay</code>). This guarantees that the same dispatch function will 319not be called with the sample display at the same time. If a driver has access 320to an <code>EGLDisplay</code> without going through the EGL APIs, the driver 321should as well lock the display before using it. 322 323<h3>TODOs</h3> 324 325<ul> 326<li>Pass the conformance tests</li> 327<li>Better automatic driver selection: <code>EGL_DISPLAY</code> loads all 328drivers and might eat too much memory.</li> 329 330</ul> 331 332</body> 333</html> 334