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>Configure your build with the desired client APIs and enable 37 the driver for your hardware. For example:</p> 38 39 <pre> 40 $ meson configure \ 41 -D egl=true \ 42 -D gles1=true \ 43 -D gles2=true \ 44 -D dri-drivers=... \ 45 -D gallium-drivers=... 46 </pre> 47 48 <p>The main library and OpenGL is enabled by default. The first two options 49 above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The last two 50 options enables the listed classic and Gallium drivers respectively.</p> 51 52 </li> 53 54 <li>Build and install Mesa as usual.</li> 55 </ol> 56 57 <p>In the given example, it will build and install <code>libEGL</code>, 58 <code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>, and one 59 or more EGL drivers.</p> 60 61 <h3>Configure Options</h3> 62 63 <p>There are several options that control the build of EGL at configuration 64 time</p> 65 66 <dl> 67 <dt><code>-D egl=true</code></dt> 68 <dd> 69 70 <p>By default, EGL is enabled. When disabled, the main library and the drivers 71 will not be built.</p> 72 73 </dd> 74 75 <dt><code>-D platforms=...</code></dt> 76 <dd> 77 78 <p>List the platforms (window systems) to support. Its argument is a comma 79 separated string such as <code>-D platforms=x11,drm</code>. It decides 80 the platforms a driver may support. The first listed platform is also used by 81 the main library to decide the native platform.</p> 82 83 <p>The available platforms are <code>x11</code>, <code>drm</code>, 84 <code>wayland</code>, <code>surfaceless</code>, <code>android</code>, 85 and <code>haiku</code>. 86 The <code>android</code> platform can either be built as a system 87 component, part of AOSP, using <code>Android.mk</code> files, or 88 cross-compiled using appropriate options. 89 The <code>haiku</code> platform can only be built with SCons or Meson. 90 Unless for special needs, the build system should 91 select the right platforms automatically.</p> 92 93 </dd> 94 95 <dt><code>-D gles1=true</code></dt> 96 <dt><code>-D gles2=true</code></dt> 97 <dd> 98 99 <p>These options enable OpenGL ES support in OpenGL. The result is one big 100 internal library that supports multiple APIs.</p> 101 102 </dd> 103 104 <dt><code>-D shared-glapi=true</code></dt> 105 <dd> 106 107 <p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>. 108 This options makes <code>libGL</code> use the shared <code>libglapi</code>. This 109 is required if applications mix OpenGL and OpenGL ES.</p> 110 111 </dd> 112 113 </dl> 114 115 <h2>Use EGL</h2> 116 117 <h3>Demos</h3> 118 119 <p>There are demos for the client APIs supported by EGL. They can be found in 120 mesa/demos repository.</p> 121 122 <h3>Environment Variables</h3> 123 124 <p>There are several environment variables that control the behavior of EGL at 125 runtime</p> 126 127 <dl> 128 <dt><code>EGL_PLATFORM</code></dt> 129 <dd> 130 131 <p>This variable specifies the native platform. The valid values are the same 132 as those for <code>-D platforms=...</code>. When the variable is not set, 133 the main library uses the first platform listed in 134 <code>-D platforms=...</code> as the native platform.</p> 135 136 <p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to 137 create displays for non-native platforms. These extensions are usually used by 138 applications that support non-native platforms. Setting this variable is 139 probably required only for some of the demos found in mesa/demo repository.</p> 140 141 </dd> 142 143 <dt><code>EGL_LOG_LEVEL</code></dt> 144 <dd> 145 146 <p>This changes the log level of the main library and the drivers. The valid 147 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and 148 <code>fatal</code>.</p> 149 150 </dd> 151 </dl> 152 153 <h2>EGL Drivers</h2> 154 155 <dl> 156 <dt><code>egl_dri2</code></dt> 157 <dd> 158 159 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms. 160 It functions as a DRI driver loader. For <code>x11</code> support, it talks to 161 the X server directly using (XCB-)DRI2 protocol.</p> 162 163 <p>This driver can share DRI drivers with <code>libGL</code>.</p> 164 165 </dd> 166 </dl> 167 168 <h2>Packaging</h2> 169 170 <p>The ABI between the main library and its drivers are not stable. Nor is 171 there a plan to stabilize it at the moment.</p> 172 173 <h2>Developers</h2> 174 175 <p>The sources of the main library and drivers can be found at 176 <code>src/egl/</code>.</p> 177 178 <h3>Lifetime of Display Resources</h3> 179 180 <p>Contexts and surfaces are examples of display resources. They might live 181 longer than the display that creates them.</p> 182 183 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all 184 display resources should be destroyed. Similarly, when a thread is released 185 through <code>eglReleaseThread</code>, all current display resources should be 186 released. Another way to destroy or release resources is through functions 187 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p> 188 189 <p>When a resource that is current to some thread is destroyed, the resource 190 should not be destroyed immediately. EGL requires the resource to live until 191 it is no longer current. A driver usually calls 192 <code>eglIs<Resource>Bound</code> to check if a resource is bound 193 (current) to any thread in the destroy callbacks. If it is still bound, the 194 resource is not destroyed.</p> 195 196 <p>The main library will mark destroyed current resources as unlinked. In a 197 driver's <code>MakeCurrent</code> callback, 198 <code>eglIs<Resource>Linked</code> can then be called to check if a newly 199 released resource is linked to a display. If it is not, the last reference to 200 the resource is removed and the driver should destroy the resource. But it 201 should be careful here because <code>MakeCurrent</code> might be called with an 202 uninitialized display.</p> 203 204 <p>This is the only mechanism provided by the main library to help manage the 205 resources. The drivers are responsible to the correct behavior as defined by 206 EGL.</p> 207 208 <h3><code>EGL_RENDER_BUFFER</code></h3> 209 210 <p>In EGL, the color buffer a context should try to render to is decided by the 211 binding surface. It should try to render to the front buffer if the binding 212 surface has <code>EGL_RENDER_BUFFER</code> set to 213 <code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a 214 surface with <code>EGL_RENDER_BUFFER</code> set to 215 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back 216 buffer. However, the context is allowed to make the final decision as to which 217 color buffer it wants to or is able to render to.</p> 218 219 <p>For pbuffer surfaces, the render buffer is always 220 <code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is 221 always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec 222 requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a 223 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or 224 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the 225 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or 226 pbuffer surfaces.</p> 227 228 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be 229 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It 230 is desirable that a driver allocates a private color buffer for each pbuffer 231 surface created. If the window system the driver supports has native pbuffers, 232 or if the native pixmaps have more than one color buffers, the driver should 233 carefully attach the native color buffers to the EGL surfaces, re-route them if 234 required.</p> 235 236 <p>There is no defined behavior as to, for example, how 237 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right 238 now, it is desired that the draw buffer in a client API be fixed for pixmap and 239 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the 240 client API renders to the specified render buffer for pixmap and pbuffer 241 surfaces.</p> 242 243 <h3><code>EGLDisplay</code> Mutex</h3> 244 245 The <code>EGLDisplay</code> will be locked before calling any of the dispatch 246 functions (well, except for GetProcAddress which does not take an 247 <code>EGLDisplay</code>). This guarantees that the same dispatch function will 248 not be called with the sample display at the same time. If a driver has access 249 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver 250 should as well lock the display before using it. 251 252 </div> 253 </body> 254 </html> 255
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