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Breadcrumbs go here --> <li><a href="all-examples.html">Examples</a></li> <li>Hello GL ES Example</li> </ul> </div> <div class="toolbuttons toolblock"> <ul> <li id="smallA" class="t_button">A</li> <li id="medA" class="t_button active">A</li> <li id="bigA" class="t_button">A</li> <li id="print" class="t_button"><a href="javascript:this.print();"> <span>Print</span></a></li> </ul> </div> </div> <div class="content mainContent"> <div class="toc"> <h3><a name="toc">Contents</a></h3> <ul> <li class="level1"><a href="#using-qglwidget">Using QGLWidget</a></li> <li class="level1"><a href="#porting-opengl-to-opengl-es">Porting OpenGL to OpenGL ES</a></li> <li class="level1"><a href="#using-qglpainter">Using QGLPainter</a></li> <li class="level1"><a href="#summary">Summary</a></li> </ul> </div> <h1 class="title">Hello GL ES Example</h1> <span class="subtitle"></span> <!-- $$$opengl/hellogl_es-description --> <div class="descr"> <a name="details"></a> <p>Files:</p> <ul> <li><a href="opengl-hellogl-es-bubble-cpp.html">opengl/hellogl_es/bubble.cpp</a></li> <li><a href="opengl-hellogl-es-bubble-h.html">opengl/hellogl_es/bubble.h</a></li> <li><a href="opengl-hellogl-es-glwidget-cpp.html">opengl/hellogl_es/glwidget.cpp</a></li> <li><a href="opengl-hellogl-es-glwidget-h.html">opengl/hellogl_es/glwidget.h</a></li> <li><a href="opengl-hellogl-es-mainwindow-cpp.html">opengl/hellogl_es/mainwindow.cpp</a></li> <li><a href="opengl-hellogl-es-mainwindow-h.html">opengl/hellogl_es/mainwindow.h</a></li> <li><a href="opengl-hellogl-es-main-cpp.html">opengl/hellogl_es/main.cpp</a></li> <li><a href="opengl-hellogl-es-hellogl-es-pro.html">opengl/hellogl_es/hellogl_es.pro</a></li> <li><a href="opengl-hellogl-es-texture-qrc.html">opengl/hellogl_es/texture.qrc</a></li> </ul> <p>The Hello GL ES example is the <a href="opengl-hellogl.html">Hello GL Example</a> ported to OpenGL ES. It also included some effects from the OpenGL <a href="opengl-overpainting.html">Overpainting Example</a>.<p class="centerAlign"><img src="images/hellogl-es-example.png" alt="" /></p><p>A complete introduction to OpenGL ES and a description of all differences between OpenGL and OpenGL ES is out of the scope of this document; but we will describe some of the major issues and differences.</p> <p>Since Hello GL ES is a direct port of standard OpenGL code, it is a fairly good example for porting OpenGL code to OpenGL ES.</p> <a name="using-qglwidget"></a> <h2>Using QGLWidget</h2> <p><a href="qglwidget.html">QGLWidget</a> can be used for OpenGL ES similar to the way it is used with standard OpenGL; but there are some differences. We use EGL 1.0 to embedd the OpenGL ES window within the native window manager. In <a href="qglwidget.html#initializeGL">QGLWidget::initializeGL</a>() we initialize OpenGL ES.</p> <a name="porting-opengl-to-opengl-es"></a> <h2>Porting OpenGL to OpenGL ES</h2> <p>Since OpenGL ES is missing the immediate mode and does not support quads, we have to create triangle arrays.</p> <p>We create a quad by adding vertices to a <a href="qlist.html">QList</a> of vertices. We create both sides of the quad and hardcode a distance of 0.05f. We also compute the correct normal for each face and store them in another <a href="qlist.html">QList</a>.</p> <pre class="cpp"> <span class="type">void</span> GLWidget<span class="operator">::</span>quad(<span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> x1<span class="operator">,</span> <span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> y1<span class="operator">,</span> <span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> x2<span class="operator">,</span> <span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> y2<span class="operator">,</span> <span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> x3<span class="operator">,</span> <span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> y3<span class="operator">,</span> <span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> x4<span class="operator">,</span> <span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> y4) { <span class="type"><a href="qtglobal.html#qreal-typedef">qreal</a></span> nx<span class="operator">,</span> ny<span class="operator">,</span> nz; vertices <span class="operator"><</span><span class="operator"><</span> x1 <span class="operator"><</span><span class="operator"><</span> y1 <span class="operator"><</span><span class="operator"><</span> <span class="operator">-</span><span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x2 <span class="operator"><</span><span class="operator"><</span> y2 <span class="operator"><</span><span class="operator"><</span> <span class="operator">-</span><span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x4 <span class="operator"><</span><span class="operator"><</span> y4 <span class="operator"><</span><span class="operator"><</span> <span class="operator">-</span><span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x3 <span class="operator"><</span><span class="operator"><</span> y3 <span class="operator"><</span><span class="operator"><</span> <span class="operator">-</span><span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x4 <span class="operator"><</span><span class="operator"><</span> y4 <span class="operator"><</span><span class="operator"><</span> <span class="operator">-</span><span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x2 <span class="operator"><</span><span class="operator"><</span> y2 <span class="operator"><</span><span class="operator"><</span> <span class="operator">-</span><span class="number">0.05f</span>; CrossProduct(nx<span class="operator">,</span> ny<span class="operator">,</span> nz<span class="operator">,</span> x2 <span class="operator">-</span> x1<span class="operator">,</span> y2 <span class="operator">-</span> y1<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> x4 <span class="operator">-</span> x1<span class="operator">,</span> y4 <span class="operator">-</span> y1<span class="operator">,</span> <span class="number">0</span>); Normalize(nx<span class="operator">,</span> ny<span class="operator">,</span> nz); normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; vertices <span class="operator"><</span><span class="operator"><</span> x4 <span class="operator"><</span><span class="operator"><</span> y4 <span class="operator"><</span><span class="operator"><</span> <span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x2 <span class="operator"><</span><span class="operator"><</span> y2 <span class="operator"><</span><span class="operator"><</span> <span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x1 <span class="operator"><</span><span class="operator"><</span> y1 <span class="operator"><</span><span class="operator"><</span> <span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x2 <span class="operator"><</span><span class="operator"><</span> y2 <span class="operator"><</span><span class="operator"><</span> <span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x4 <span class="operator"><</span><span class="operator"><</span> y4 <span class="operator"><</span><span class="operator"><</span> <span class="number">0.05f</span>; vertices <span class="operator"><</span><span class="operator"><</span> x3 <span class="operator"><</span><span class="operator"><</span> y3 <span class="operator"><</span><span class="operator"><</span> <span class="number">0.05f</span>; CrossProduct(nx<span class="operator">,</span> ny<span class="operator">,</span> nz<span class="operator">,</span> x2 <span class="operator">-</span> x4<span class="operator">,</span> y2 <span class="operator">-</span> y4<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> x1 <span class="operator">-</span> x4<span class="operator">,</span> y1 <span class="operator">-</span> y4<span class="operator">,</span> <span class="number">0</span>); Normalize(nx<span class="operator">,</span> ny<span class="operator">,</span> nz); normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; normals <span class="operator"><</span><span class="operator"><</span> nx <span class="operator"><</span><span class="operator"><</span> ny <span class="operator"><</span><span class="operator"><</span> nz; }</pre> <p>And then we convert the complete list of vertexes and the list of normals into the native OpenGL ES format that we can use with the OpenGL ES API.</p> <pre class="cpp"> m_vertexNumber <span class="operator">=</span> vertices<span class="operator">.</span>size(); createdVertices <span class="operator">=</span> <span class="keyword">new</span> GLfloat<span class="operator">[</span>m_vertexNumber<span class="operator">]</span>; createdNormals <span class="operator">=</span> <span class="keyword">new</span> GLfloat<span class="operator">[</span>m_vertexNumber<span class="operator">]</span>; <span class="keyword">for</span> (<span class="type">int</span> i <span class="operator">=</span> <span class="number">0</span>;i <span class="operator"><</span> m_vertexNumber;i<span class="operator">+</span><span class="operator">+</span>) { createdVertices<span class="operator">[</span>i<span class="operator">]</span> <span class="operator">=</span> vertices<span class="operator">.</span>at(i) <span class="operator">*</span> <span class="number">2</span>; createdNormals<span class="operator">[</span>i<span class="operator">]</span> <span class="operator">=</span> normals<span class="operator">.</span>at(i); } vertices<span class="operator">.</span>clear(); normals<span class="operator">.</span>clear(); }</pre> <p>In <tt>paintQtLogo()</tt> we draw the triangle array using OpenGL ES. We use q_vertexTypeEnum to abstract the fact that our vertex and normal arrays are either in float or in fixed point format.</p> <pre class="cpp"> <span class="type">void</span> GLWidget<span class="operator">::</span>paintQtLogo() { glDisable(GL_TEXTURE_2D); glEnableClientState(GL_VERTEX_ARRAY); glVertexPointer(<span class="number">3</span><span class="operator">,</span>GL_FLOAT<span class="operator">,</span><span class="number">0</span><span class="operator">,</span> createdVertices); glEnableClientState(GL_NORMAL_ARRAY); glNormalPointer(GL_FLOAT<span class="operator">,</span><span class="number">0</span><span class="operator">,</span>createdNormals); glDrawArrays(GL_TRIANGLES<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> m_vertexNumber <span class="operator">/</span> <span class="number">3</span>); }</pre> <a name="using-qglpainter"></a> <h2>Using QGLPainter</h2> <p>Since the <tt>QGLPainter</tt> is slower for OpenGL ES we paint the bubbles with the rasterizer and cache them in a <a href="qimage.html">QImage</a>. This happends only once during the initialiazation.</p> <pre class="cpp"> <span class="type">void</span> Bubble<span class="operator">::</span>updateCache() { <span class="keyword">if</span> (cache) <span class="keyword">delete</span> cache; cache <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qimage.html">QImage</a></span>(<a href="qtglobal.html#qRound">qRound</a>(radius <span class="operator">*</span> <span class="number">2</span> <span class="operator">+</span> <span class="number">2</span>)<span class="operator">,</span> <a href="qtglobal.html#qRound">qRound</a>(radius <span class="operator">*</span> <span class="number">2</span> <span class="operator">+</span> <span class="number">2</span>)<span class="operator">,</span> <span class="type"><a href="qimage.html">QImage</a></span><span class="operator">::</span>Format_ARGB32); cache<span class="operator">-</span><span class="operator">></span>fill(<span class="number">0x00000000</span>); <span class="type"><a href="qpainter.html">QPainter</a></span> p(cache); p<span class="operator">.</span>setRenderHint(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>HighQualityAntialiasing); <span class="type"><a href="qpen.html">QPen</a></span> pen(<span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>white); pen<span class="operator">.</span>setWidth(<span class="number">2</span>); p<span class="operator">.</span>setPen(pen); p<span class="operator">.</span>setBrush(brush); p<span class="operator">.</span>drawEllipse(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="type">int</span>(<span class="number">2</span><span class="operator">*</span>radius)<span class="operator">,</span> <span class="type">int</span>(<span class="number">2</span><span class="operator">*</span>radius)); }</pre> <p>For each bubble this <a href="qimage.html">QImage</a> is then drawn to the <a href="qglwidget.html">QGLWidget</a> by using the according <a href="qpainter.html">QPainter</a> with transparency enabled.</p> <pre class="cpp"> <span class="type">void</span> Bubble<span class="operator">::</span>drawBubble(<span class="type"><a href="qpainter.html">QPainter</a></span> <span class="operator">*</span>painter) { painter<span class="operator">-</span><span class="operator">></span>save(); painter<span class="operator">-</span><span class="operator">></span>translate(position<span class="operator">.</span>x() <span class="operator">-</span> radius<span class="operator">,</span> position<span class="operator">.</span>y() <span class="operator">-</span> radius); painter<span class="operator">-</span><span class="operator">></span>setOpacity(<span class="number">0.8</span>); painter<span class="operator">-</span><span class="operator">></span>drawImage(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="operator">*</span>cache); painter<span class="operator">-</span><span class="operator">></span>restore(); }</pre> <p>Another difference beetwen OpenGL and OpenGL ES is that OpenGL ES does not support glPushAttrib(GL_ALL_ATTRIB_BITS). So we have to restore all the OpenGL states ourselves, after we created the <a href="qpainter.html">QPainter</a> in GLWidget::paintGL().</p> <pre class="cpp"> <span class="type"><a href="qpainter.html">QPainter</a></span> painter; painter<span class="operator">.</span>begin(<span class="keyword">this</span>); glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity();</pre> <p>Setting up up the model view matrix and setting the right OpenGL states is done in the same way as for standard OpenGL.</p> <pre class="cpp"> glMatrixMode(GL_MODELVIEW); glPushMatrix(); glMatrixMode(GL_TEXTURE); glPushMatrix(); <span class="comment">//Since OpenGL ES does not support glPush/PopAttrib(GL_ALL_ATTRIB_BITS)</span> <span class="comment">//we have to take care of the states ourselves</span> glClearColor(<span class="number">0.1f</span><span class="operator">,</span> <span class="number">0.1f</span><span class="operator">,</span> <span class="number">0.2f</span><span class="operator">,</span> <span class="number">1.0f</span>); glClear(GL_COLOR_BUFFER_BIT <span class="operator">|</span> GL_DEPTH_BUFFER_BIT); glEnable(GL_TEXTURE_2D); glTexParameterf(GL_TEXTURE_2D<span class="operator">,</span> GL_TEXTURE_MIN_FILTER<span class="operator">,</span> GL_LINEAR ); glTexParameterf(GL_TEXTURE_2D<span class="operator">,</span> GL_TEXTURE_MAG_FILTER<span class="operator">,</span> GL_LINEAR ); glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); glShadeModel(GL_FLAT); glFrontFace(GL_CW); glCullFace(GL_FRONT); glEnable(GL_CULL_FACE); glEnable(GL_DEPTH_TEST); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glRotatef(m_fAngle<span class="operator">,</span> <span class="number">0.0f</span><span class="operator">,</span> <span class="number">1.0f</span><span class="operator">,</span> <span class="number">0.0f</span>); glRotatef(m_fAngle<span class="operator">,</span> <span class="number">1.0f</span><span class="operator">,</span> <span class="number">0.0f</span><span class="operator">,</span> <span class="number">0.0f</span>); glRotatef(m_fAngle<span class="operator">,</span> <span class="number">0.0f</span><span class="operator">,</span> <span class="number">0.0f</span><span class="operator">,</span> <span class="number">1.0f</span>); glScalef(m_fScale<span class="operator">,</span> m_fScale<span class="operator">,</span>m_fScale); glTranslatef(<span class="number">0.0f</span><span class="operator">,</span><span class="operator">-</span><span class="number">0.2f</span><span class="operator">,</span><span class="number">0.0f</span>); GLfloat matDiff<span class="operator">[</span><span class="operator">]</span> <span class="operator">=</span> {<span class="number">0.40f</span><span class="operator">,</span> <span class="number">1.0f</span><span class="operator">,</span> <span class="number">0.0f</span><span class="operator">,</span> <span class="number">1.0f</span>}; glMaterialfv(GL_FRONT_AND_BACK<span class="operator">,</span> GL_DIFFUSE<span class="operator">,</span> matDiff); <span class="keyword">if</span> (qtLogo) paintQtLogo(); <span class="keyword">else</span> paintTexturedCube();</pre> <p>Now we have to restore the OpenGL state for the <a href="qpainter.html">QPainter</a>. This is not done automatically for OpenGL ES.</p> <pre class="cpp"> glMatrixMode(GL_MODELVIEW); glPopMatrix(); glMatrixMode(GL_PROJECTION); glPopMatrix(); glMatrixMode(GL_TEXTURE); glPopMatrix(); glDisable(GL_LIGHTING); glDisable(GL_LIGHT0); glDisable(GL_DEPTH_TEST); glDisable(GL_CULL_FACE);</pre> <p>Now we use the <a href="qpainter.html">QPainter</a> to draw the transparent bubbles.</p> <pre class="cpp"> <span class="keyword">if</span> (m_showBubbles) foreach (Bubble <span class="operator">*</span>bubble<span class="operator">,</span> bubbles) { bubble<span class="operator">-</span><span class="operator">></span>drawBubble(<span class="operator">&</span>painter); }</pre> <p>In the end, we calculate the framerate and display it using the <a href="qpainter.html">QPainter</a> again.</p> <pre class="cpp"> <span class="type"><a href="qstring.html">QString</a></span> framesPerSecond; framesPerSecond<span class="operator">.</span>setNum(frames <span class="operator">/</span>(time<span class="operator">.</span>elapsed() <span class="operator">/</span> <span class="number">1000.0</span>)<span class="operator">,</span> <span class="char">'f'</span><span class="operator">,</span> <span class="number">2</span>); painter<span class="operator">.</span>setPen(<span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>white); painter<span class="operator">.</span>drawText(<span class="number">20</span><span class="operator">,</span> <span class="number">40</span><span class="operator">,</span> framesPerSecond <span class="operator">+</span> <span class="string">" fps"</span>); painter<span class="operator">.</span>end();</pre> <p>After we finished all the drawing operations we swap the screen buffer.</p> <pre class="cpp"> swapBuffers();</pre> <a name="summary"></a> <h2>Summary</h2> <p>Similar to the <a href="opengl-hellogl.html">Hello GL Example</a>, we subclass <a href="qglwidget.html">QGLWidget</a> to render a 3D scene using OpenGL ES calls. <a href="qglwidget.html">QGLWidget</a> is a subclass of <a href="qwidget.html">QWidget</a>. Hence, its <a href="qglwidget.html">QGLWidget</a>'s subclasses can be placed in layouts and provided with interactive features just like normal custom widgets.</p> <p><a href="qglwidget.html">QGLWidget</a> allows pure OpenGL ES rendering to be mixed with <a href="qpainter.html">QPainter</a> calls, but care must be taken to maintain the state of the OpenGL ES implementation.</p> </div> <!-- @@@opengl/hellogl_es --> </div> </div> </div> <div class="ft"> <span></span> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2013 Digia Plc and/or its subsidiaries. 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