egl.html revision c6320c5eb20d1ab20ad7800aceedc5dd8762dfeb
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 --enable-openvg --enable-gallium-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 second option enables 40<a href="openvg.html">OpenVG</a>. 41</p> 42 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-platforms</code> 73 74<p>List the platforms (window systems) to support. Its argument is a comma 75seprated string such as <code>--with-egl-platforms=x11,drm</code>. It decides 76the platforms a driver may support. The first listed platform is also used by 77the main library to decide the native platform: the platform the EGL native 78types such as <code>EGLNativeDisplayType</code> or 79<code>EGLNativeWindowType</code> defined for.</p> 80 81<p>The available platforms are <code>x11</code>, <code>drm</code>, 82<code>fbdev</code>, and <code>gdi</code>. The <code>gdi</code> platform can 83only be built with SCons.</p> 84 85</li> 86 87<li><code>--enable-gles-overlay</code> 88 89<p>OpenGL is built by default. To build OpenGL ES, this option must be 90explicitly given.</p> 91 92</li> 93 94<li><code>--enable-gles1</code> and <code>--enable-gles2</code> 95 96<p>Unlike <code>--enable-gles-overlay</code>, which builds one library for each 97rendering API, these options enable OpenGL ES support in OpenGL. The result is 98one big library that supports multiple APIs.</p> 99 100</li> 101 102<li><code>--enable-openvg</code> 103 104<p>OpenVG must be explicitly enabled by this option.</p> 105 106</li> 107 108</ul> 109 110<h2>Use EGL</h2> 111 112<h3>Demos</h3> 113 114<p>There are demos for the client APIs supported by EGL. They can be found in 115mesa/demos repository.</p> 116 117<h3>Environment Variables</h3> 118 119<p>There are several environment variables that control the behavior of EGL at 120runtime</p> 121 122<ul> 123<li><code>EGL_DRIVERS_PATH</code> 124 125<p>By default, the main library will look for drivers in the directory where 126the drivers are installed to. This variable specifies a list of 127colon-separated directories where the main library will look for drivers, in 128addition to the default directory. This variable is ignored for setuid/setgid 129binaries.</p> 130 131</li> 132 133<li><code>EGL_DRIVER</code> 134 135<p>This variable specifies a full path to an EGL driver and it forces the 136specified EGL driver to be loaded. It comes in handy when one wants to test a 137specific driver. This variable is ignored for setuid/setgid binaries.</p> 138 139<p><code>egl_gallium</code> dynamically loads hardware drivers and client API 140modules found in <code>EGL_DRIVERS_PATH</code>. Thus, specifying this variable 141alone is not sufficient for <code>egl_gallium</code> for an uninstalled 142build.</p> 143 144</li> 145 146<li><code>EGL_PLATFORM</code> 147 148<p>This variable specifies the native platform. The valid values are the same 149as those for <code>--with-egl-platforms</code>. When the variable is not set, 150the main library uses the first platform listed in 151<code>--with-egl-platforms</code> as the native platform</p> 152 153</li> 154 155<li><code>EGL_LOG_LEVEL</code> 156 157<p>This changes the log level of the main library and the drivers. The valid 158values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and 159<code>fatal</code>.</p> 160 161</li> 162 163<li><code>EGL_SOFTWARE</code> 164 165<p>For drivers that support both hardware and software rendering, setting this 166variable to true forces the use of software rendering.</p> 167 168</li> 169</ul> 170 171<h2>EGL Drivers</h2> 172 173<ul> 174<li><code>egl_gallium</code> 175 176<p>This driver is based on Gallium3D. It supports all rendering APIs and 177hardwares supported by Gallium3D. It is the only driver that supports OpenVG. 178The supported platforms are X11, DRM, FBDEV, and GDI.</p> 179 180</li> 181 182<li><code>egl_glx</code> 183 184<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement 185the EGL API. It supports both direct and indirect rendering when the GLX does. 186It is accelerated when the GLX is. As such, it cannot provide functions that 187is not available in GLX or GLX extensions.</p> 188</li> 189 190<li><code>egl_dri2</code> 191 192<p>This driver supports the X Window System as its window system. It functions 193as a DRI2 driver loader. Unlike <code>egl_glx</code>, it has no dependency on 194<code>libGL</code>. It talks to the X server directly using (XCB-)DRI2 195protocol.</p> 196 197</li> 198</ul> 199 200<h2>Developers</h2> 201 202<p>The sources of the main library and the classic drivers can be found at 203<code>src/egl/</code>. The sources of the <code>egl</code> state tracker can 204be found at <code>src/gallium/state_trackers/egl/</code>.</p> 205 206<p>The suggested way to learn to write a EGL driver is to see how other drivers 207are written. <code>egl_glx</code> should be a good reference. It works in any 208environment that has GLX support, and it is simpler than most drivers.</p> 209 210<h3>Lifetime of Display Resources</h3> 211 212<p>Contexts and surfaces are examples of display resources. They might live 213longer than the display that creates them.</p> 214 215<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all 216display resources should be destroyed. Similarly, when a thread is released 217throught <code>eglReleaseThread</code>, all current display resources should be 218released. Another way to destory or release resources is through functions 219such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p> 220 221<p>When a resource that is current to some thread is destroyed, the resource 222should not be destroyed immediately. EGL requires the resource to live until 223it is no longer current. A driver usually calls 224<code>eglIs<Resource>Bound</code> to check if a resource is bound 225(current) to any thread in the destroy callbacks. If it is still bound, the 226resource is not destroyed.</p> 227 228<p>The main library will mark destroyed current resources as unlinked. In a 229driver's <code>MakeCurrent</code> callback, 230<code>eglIs<Resource>Linked</code> can then be called to check if a newly 231released resource is linked to a display. If it is not, the last reference to 232the resource is removed and the driver should destroy the resource. But it 233should be careful here because <code>MakeCurrent</code> might be called with an 234uninitialized display.</p> 235 236<p>This is the only mechanism provided by the main library to help manage the 237resources. The drivers are responsible to the correct behavior as defined by 238EGL.</p> 239 240<h3><code>EGL_RENDER_BUFFER</code></h3> 241 242<p>In EGL, the color buffer a context should try to render to is decided by the 243binding surface. It should try to render to the front buffer if the binding 244surface has <code>EGL_RENDER_BUFFER</code> set to 245<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a 246surface with <code>EGL_RENDER_BUFFER</code> set to 247<code>EGL_BACK_BUFFER</code>, the context should try to render to the back 248buffer. However, the context is allowed to make the final decision as to which 249color buffer it wants to or is able to render to.</p> 250 251<p>For pbuffer surfaces, the render buffer is always 252<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is 253always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec 254requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a 255result, a driver should never set <code>EGL_PIXMAP_BIT</code> or 256<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the 257config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or 258pbuffer surfaces.</p> 259 260<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be 261single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It 262is desirable that a driver allocates a private color buffer for each pbuffer 263surface created. If the window system the driver supports has native pbuffers, 264or if the native pixmaps have more than one color buffers, the driver should 265carefully attach the native color buffers to the EGL surfaces, re-route them if 266required.</p> 267 268<p>There is no defined behavior as to, for example, how 269<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right 270now, it is desired that the draw buffer in a client API be fixed for pixmap and 271pbuffer surfaces. Therefore, the driver is responsible to guarantee that the 272client API renders to the specified render buffer for pixmap and pbuffer 273surfaces.</p> 274 275<h3><code>EGLDisplay</code> Mutex</h3> 276 277The <code>EGLDisplay</code> will be locked before calling any of the dispatch 278functions (well, except for GetProcAddress which does not take an 279<code>EGLDisplay</code>). This guarantees that the same dispatch function will 280not be called with the sample display at the same time. If a driver has access 281to an <code>EGLDisplay</code> without going through the EGL APIs, the driver 282should as well lock the display before using it. 283 284<h3>TODOs</h3> 285 286<ul> 287<li>Pass the conformance tests</li> 288<li>Mixed use of OpenGL, OpenGL ES 1.1, and OpenGL ES 2.0 is supported. But 289which one of <code>libGL.so</code>, <code>libGLESv1_CM.so</code>, and 290<code>libGLESv2.so</code> should an application link to? Bad things may happen 291when, say, an application is linked to <code>libGLESv2.so</code> and 292<code>libcairo</code>, which is linked to <code>libGL.so</code> instead.</li> 293 294</ul> 295 296</body> 297</html> 298