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<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>
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<h1 class="title">Hello GL ES Example</h1>
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<!-- $$$opengl/hellogl_es-description -->
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<p>Files:</p>
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<li><a href="opengl-hellogl-es-bubble-cpp.html">opengl/hellogl_es/bubble.cpp</a></li>
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<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>
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