1<?xml version="1.0" encoding="UTF-8"?> 2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN" 3 "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd"> 4<refentry xml:base="" id="eglIntro"> 5 <refentryinfo> 6 <copyright> 7 <year>2003-2014</year> 8 <holder>The Khronos Group Inc.</holder> 9 </copyright> 10 </refentryinfo> 11 <refmeta> 12 <refentrytitle>eglIntro</refentrytitle> 13 <manvolnum>3G</manvolnum> 14 </refmeta> 15 <refnamediv> 16 <refname>eglIntro</refname> 17 <refpurpose> 18 introduction to managing client API rendering through the 19 <acronym>EGL</acronym> API. 20 </refpurpose> 21 </refnamediv> 22 <refsect1 id="overview"><title>Overview</title> 23 <para> 24 The <firstterm>Khronos Native Platform Graphics 25 Interface</firstterm> (EGL) provides a means for rendering 26 using a <firstterm>client API</firstterm> such as OpenGL ES 27 (a 3D renderer for embedded systems), OpenGL (a functional 28 superset of OpenGL ES for desktop systems), and OpenVG (a 2D 29 vector graphics renderer) together with a native window 30 system, such as Microsoft Windows or the X Window System. 31 </para> 32 <para> 33 Depending on its implementation EGL might be more or less 34 tightly integrated into the native window system. Most EGL 35 functions require an EGL display connection, which can be 36 obtained by calling 37 <citerefentry><refentrytitle>eglGetDisplay</refentrytitle></citerefentry> 38 and passing in a native display handle or 39 <constant>EGL_DEFAULT_DISPLAY</constant>. To initialize and 40 query what EGL version is supported on the display 41 connection, call 42 <citerefentry><refentrytitle>eglInitialize</refentrytitle></citerefentry>. 43 </para> 44 <para> 45 Native window systems supporting EGL make a subset of their 46 visuals (which may also referred to as pixel formats, frame 47 buffer configurations, or other similar terms) available for 48 client API rendering. Windows and pixmaps created with these 49 visuals may also be rendered into using the native window 50 system API. 51 </para> 52 <para> 53 An EGL <firstterm>surface</firstterm> extends a native 54 window or pixmap with additional <firstterm>auxillary 55 buffers</firstterm>. These buffers include a color buffer, a 56 depth buffer, a stencil buffer, and an alpha mask buffer. 57 Some or all of the buffers listed are included in each EGL 58 frame buffer configuration. 59 </para> 60 <para> 61 EGL supports rendering into three types of surfaces: 62 windows, pixmaps and pixel buffers (pbuffers). EGL window 63 and pixmap surfaces are associated with corresponding 64 resources of the native window system. EGL pixel buffers are 65 EGL only resources, and do not accept rendering through the 66 native window system. 67 </para> 68 <para> 69 To render using a client API into an EGL surface, you must 70 determine the appropriate EGL frame buffer configuration, 71 which supports the rendering features the application 72 requires. 73 <citerefentry><refentrytitle>eglChooseConfig</refentrytitle></citerefentry> 74 returns an <type>EGLConfig</type> matching the required 75 attributes, if any. A complete list of EGL frame buffer 76 configurations can be obtained by calling 77 <citerefentry><refentrytitle>eglGetConfigs</refentrytitle></citerefentry>. 78 Attributes of a particular EGL frame buffer configuration 79 can be queried by calling 80 <citerefentry><refentrytitle>eglGetConfigAttrib</refentrytitle></citerefentry>. 81 </para> 82 <para> 83 For EGL window and pixmap surfaces, a suitable native window 84 or pixmap with a matching native visual must be created 85 first. For a given EGL frame buffer configuration, the 86 native visual type and ID can be retrieved with a call to 87 <citerefentry><refentrytitle>eglGetConfigAttrib</refentrytitle></citerefentry>. 88 For pixel buffers, no underlying native resource is 89 required. 90 </para> 91 <para> 92 To create an EGL window surface from a native window, call 93 <citerefentry><refentrytitle>eglCreateWindowSurface</refentrytitle></citerefentry>. 94 To create an EGL pixmap surface from a native pixmap, call 95 <citerefentry><refentrytitle>eglCreatePixmapSurface</refentrytitle></citerefentry>. 96 To create a pixel buffer (pbuffer) surface (which has no 97 associated native buffer), call 98 <citerefentry><refentrytitle>eglCreatePbufferSurface</refentrytitle></citerefentry> 99 To create a pixel buffer (pbuffer) surface whose color 100 buffer is provided by an OpenVG <type>VGImage</type>, call 101 <citerefentry><refentrytitle>eglCreatePbufferFromClientBuffer</refentrytitle></citerefentry>. 102 Use 103 <citerefentry><refentrytitle>eglDestroySurface</refentrytitle></citerefentry> 104 to release previously allocated resources. 105 </para> 106 <para> 107 An EGL rendering context is required to bind client API 108 rendering to an EGL surface. An EGL surface and an EGL 109 rendering context must have compatible EGL frame buffer 110 configurations. To create an EGL rendering context, call 111 <citerefentry><refentrytitle>eglCreateContext</refentrytitle></citerefentry>. 112 The type of client API context created (OpenGL ES, OpenVG, 113 etc.) can be changed by first calling 114 <citerefentry><refentrytitle>eglBindAPI</refentrytitle></citerefentry>. 115 </para> 116 <para> 117 An EGL rendering context may be bound to one or two EGL 118 surfaces by calling 119 <citerefentry><refentrytitle>eglMakeCurrent</refentrytitle></citerefentry>. 120 This context/surface(s) association specifies the 121 <firstterm>current context</firstterm> and 122 <firstterm>current surface</firstterm>, and is used by all 123 client API rendering commands for the bound context until 124 <citerefentry><refentrytitle>eglMakeCurrent</refentrytitle></citerefentry> 125 is called with different arguments. 126 </para> 127 <para> 128 Both native and client API commands may be used to operate 129 on certain surfaces, however, the two command streams are 130 not synchronized. Synchronization can be explicitly 131 specified using by calling 132 <citerefentry><refentrytitle>eglWaitCLient</refentrytitle></citerefentry>, 133 <citerefentry><refentrytitle>eglWaitNative</refentrytitle></citerefentry>, 134 and possibly by calling other native window system commands. 135 </para> 136 </refsect1> 137 <refsect1 id="examples"><title>Examples</title> 138 <para> 139 Below is a minimal example of creating an RGBA-format window that 140 allows rendering with OpenGL ES. 141 The window is cleared to yellow when the program runs. For simplicity, 142 the program does not check for any errors. 143 </para> 144<programlisting> 145#include <stdlib.h> 146#include <unistd.h> 147#include <EGL/egl.h> 148#include <GLES/gl.h> 149typedef ... NativeWindowType; 150extern NativeWindowType createNativeWindow(void); 151static EGLint const attribute_list[] = { 152 EGL_RED_SIZE, 1, 153 EGL_GREEN_SIZE, 1, 154 EGL_BLUE_SIZE, 1, 155 EGL_NONE 156}; 157int main(int argc, char ** argv) 158{ 159 EGLDisplay display; 160 EGLConfig config; 161 EGLContext context; 162 EGLSurface surface; 163 NativeWindowType native_window; 164 EGLint num_config; 165 166 /* get an EGL display connection */ 167 display = eglGetDisplay(EGL_DEFAULT_DISPLAY); 168 169 /* initialize the EGL display connection */ 170 eglInitialize(display, NULL, NULL); 171 172 /* get an appropriate EGL frame buffer configuration */ 173 eglChooseConfig(display, attribute_list, &config, 1, &num_config); 174 175 /* create an EGL rendering context */ 176 context = eglCreateContext(display, config, EGL_NO_CONTEXT, NULL); 177 178 /* create a native window */ 179 native_window = createNativeWindow(); 180 181 /* create an EGL window surface */ 182 surface = eglCreateWindowSurface(display, config, native_window, NULL); 183 184 /* connect the context to the surface */ 185 eglMakeCurrent(display, surface, surface, context); 186 187 /* clear the color buffer */ 188 glClearColor(1.0, 1.0, 0.0, 1.0); 189 glClear(GL_COLOR_BUFFER_BIT); 190 glFlush(); 191 192 eglSwapBuffers(display, surface); 193 194 sleep(10); 195 return EXIT_SUCCESS; 196} 197</programlisting> 198 </refsect1> 199 <refsect1 id="usingeglextensions"><title>Using EGL Extensions</title> 200 <para> 201 All supported EGL extensions will have a corresponding definition in 202 <filename>egl.h</filename> and a token in the extensions string returned 203 by 204 <citerefentry><refentrytitle>eglQueryString</refentrytitle></citerefentry>. 205 </para> 206 </refsect1> 207 <refsect1 id="futureeglversions"><title>Future EGL Versions</title> 208 <para> 209 <citerefentry><refentrytitle>eglInitialize</refentrytitle></citerefentry> 210 and 211 <citerefentry><refentrytitle>eglQueryString</refentrytitle></citerefentry> 212 can be used to determine at run-time what version of EGL is available. 213 To check the EGL version at compile-time, test whether 214 <constant>EGL_VERSION_<replaceable>x</replaceable>_<replaceable>y</replaceable></constant> 215 is defined, where <replaceable>x</replaceable> and 216 <replaceable>y</replaceable> are the major and minor version 217 numbers. 218 </para> 219 </refsect1> 220 <refsect1 id="files"><title>Files</title> 221 <variablelist> 222 <varlistentry> 223 <term><filename>GLES/egl.h</filename></term> 224 <listitem><para> 225 EGL header file 226 </para></listitem> 227 </varlistentry> 228 </variablelist> 229 </refsect1> 230 <refsect1 id="seealso"><title>See Also</title> 231 <para> 232<!-- 233 <citerefentry><refentrytitle>glIntro</refentrytitle></citerefentry>, 234 <citerefentry><refentrytitle>glFinish</refentrytitle></citerefentry>, 235 <citerefentry><refentrytitle>glFlush</refentrytitle></citerefentry>, 236--> 237 <citerefentry><refentrytitle>eglBindAPI</refentrytitle></citerefentry>, 238 <citerefentry><refentrytitle>eglChooseConfig</refentrytitle></citerefentry>, 239 <citerefentry><refentrytitle>eglCreateContext</refentrytitle></citerefentry>, 240 <citerefentry><refentrytitle>eglCreatePbufferFromClientBuffer</refentrytitle></citerefentry>, 241 <citerefentry><refentrytitle>eglCreatePbufferSurface</refentrytitle></citerefentry>, 242 <citerefentry><refentrytitle>eglCreatePixmapSurface</refentrytitle></citerefentry>, 243 <citerefentry><refentrytitle>eglCreateWindowSurface</refentrytitle></citerefentry>, 244 <citerefentry><refentrytitle>eglDestroyContext</refentrytitle></citerefentry>, 245 <citerefentry><refentrytitle>eglDestroySurface</refentrytitle></citerefentry>, 246 <citerefentry><refentrytitle>eglGetConfigs</refentrytitle></citerefentry>, 247 <citerefentry><refentrytitle>eglGetDisplay</refentrytitle></citerefentry>, 248 <citerefentry><refentrytitle>eglInitialize</refentrytitle></citerefentry>, 249 <citerefentry><refentrytitle>eglMakeCurrent</refentrytitle></citerefentry>, 250 <citerefentry><refentrytitle>eglQueryString</refentrytitle></citerefentry>, 251 <citerefentry><refentrytitle>eglSwapBuffers</refentrytitle></citerefentry>, 252 <citerefentry><refentrytitle>eglTerminate</refentrytitle></citerefentry>, 253 <citerefentry><refentrytitle>eglWaitGL</refentrytitle></citerefentry>, 254 <citerefentry><refentrytitle>eglWaitNative</refentrytitle></citerefentry> 255 </para> 256 </refsect1> 257 <refsect3 id="Copyright"><title></title> 258 <!-- Content included from copyright.inc.xsl --> 259 <imageobject> 260 <imagedata fileref="KhronosLogo.jpg" format="jpg" /> 261 </imageobject> 262 <para /> 263 </refsect3> 264</refentry> 265
