Revision as of 11:44, 24 May 2012 by tuohirv (Talk | contribs)

Showing ads in OpenGL ES context

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This article explains how to manually fetch banner advertisements from Inneractive, display them in a 3D cube using OpenGL and opening a browser when a cube's side is clicked.

Article Metadata
Tested with
SDK: Qt SDK 4.7.4
Platform(s): Symbian^3 and later
Device(s): OpenGL required (all current Symbian^3 devices except Nokia 500
Dependencies: Inneractive's server Api
Keywords: custom advertisement opengl es context ad texture picker
Created: [[User::tuohirv]] (25 May 2012)
Last edited: tuohirv (24 May 2012)



There are several ways to make money with your application. One that is currently quite interesting especially for smaller developers is advertising. Currently, there are no built-in advertisement platform for the Symbian devices, but there are a third-party one officially recommended by Nokia: Inneractive. They provide a wide variety of different SDK's which can be quite easily be integrated for your application. Inneractive does not currently have any solution for using their SDK within 3D content. However, they do provide a simple and robust HTTP-protocol for custom purposes. This article/example deploys that SDK and explains howto use them in a QtOpenGL Symbian^3 application.

The example applcation



The Inneractive's server SDK is completely implemented in this class. The main princible is that the object owns one QNetworkAccessManager, which it uses to fetch new advertisements to be stored in-class linked list of IACapsule's which will contain the advertisement information. IAEngine is ment to be as simple as possible as seen from it's very simple interface: {{{ bool requestAd(); int getCapsuleCount(); IACapsule *getCapsule( int index ); void releaseCapsules(); }}}

requestAd starts a fetching of a new advertisement IF NO REQUEST currently exists (Only one at the time). getCapsuleCount returns the size of a in-class IACapsule list; how many advertisement we currently have stored. getCapsule returns a requested capsule by index for application to use anyway it want's and releaseCapsules destroys the whole list.


The IACapsule is just a holder for a single advertisement's information. IAEngine creates these and fills them when it's requests complete. It's properties are public for easy access.


bool m_failed; // true if some requests for this ad have been failed QString text; // Text string associated with this Ad QString targetUrl; // Url to launch when this Ad is "clicked" QString imageUrl; // Url to image (banner) of this Ad QImage m_image; // Fetched and decoded image for displaying



TODO: This will be changed to Qt SDK's own XML parser. For fast developement purposes i've been using my own, simplest possible XML parser XMLE. The code is as platform independent as possible (It has Qt bindings only to QByteArray and QIODevice). It parses small XML chunks very fast and in a very practical memory structure. For this example, XMLE is used for reading the specific information from the data required from Inneractive's server API.

= Widget

"As-simple-as-possible" QGLWidget based OpenGL ES 2.0 cube-renderer with minimal vertex / fragment shaders. The most complex part of it is the quad-picking required for knowing which side of the cube user has clicked. It will be explained in separate chapter later.

Widget owns a IAEngine which it calls to update it's advertisements until the amount of capsules reaches 6 (each side of the cube have it's own advertisement. The advertisements are burned in a single QImage with QPainter so only one texture is used for the entire cube. This QImage / GL texture is updated whenever advertisement list is changed. The advertisements are placed in a texture from top to bottom each of them using the whole width of the texture.

Picking a quad =

Since this example is working with a cube. I've decided to use quads in the picking instead of triangles. However the princible can be easily extended to triangles. Since this example only has 6 quads, the picking code is not optimized but tried to keep as simple as possible.

The main princible is that when click arrives application does similar transformation on CPU side for the cube's vertices than OpenGL ES does when rendering. These screen coordinates are then used to see if the click-coordinate is inside a quad or not.

Deploying view / projection transformation manually

The vertex shader in this example uses separate orientation and projection matrices to make the transformation more clean. The vertex - shader looks like this: {{{ attribute highp vec4 vertex; attribute highp vec2 uv; uniform mediump mat4 matrix; uniform mediump mat4 proj; varying highp vec4 frag_pos; varying mediump vec2 texCoord; void main(void) { frag_pos = matrix * vertex;

   texCoord = uv;
   gl_Position = proj*frag_pos;

} }}}

The corresponding transformation can be done like this:

{{{ void Widget::transformVector( QVector3D source, QVector3D &target ) {

   QVector4D trans = m_projection * (m_orientation*QVector4D( source, 1.0f));
   target = QVector3D( trans.x() / (NEARPLANE+trans.z()) * width()/2 + width()/2,
                       -trans.y() / (NEARPLANE+trans.z()) * height()/2 + height()/2,
                       trans.z() );

} }}}

Backface culling

There are several methods implementing backface culling. I have always used just a 2D cross-product which, in my opinion, is the best and simplest:

{{{ QVector3D tTemp[4]; // Quad screen coordinates // Any 2D vector between 2 points of the quad float tx1 = tTemp[3].x() - tTemp[0].x(); float ty1 = tTemp[3].y() - tTemp[0].y(); // Any other 2D vector between 2 points of the quad float tx2 = tTemp[1].x() - tTemp[0].x(); float ty2 = tTemp[1].y() - tTemp[0].y(); // Cross product float crosstest = tx1*ty2 - ty1*tx2; }}}

if crosstest is below zero, the quad is facing away from the camera.

Inside a quad

The princible used by this example can be extended VERY easily to cover all convex polygons and quite easily to cover convex-polygons as well. In the name of simplicity, following function only works with quads.

{{{ bool Widget::pointInsideQuad( float x, float y, QVector3D *quad ) {

   int edgecount=0;
   float xedges[2];
   int p1, p2;
   int point=0;
   const int edgePoints[] = {0,1,2,3,0,2,1,3};
   while (point<4) {
       p1 = edgePoints[point*2+0];
       p2 = edgePoints[point*2+1];
       // Order the points so p1.y is always smaller than p2.y
       if (quad[p1].y()>quad[p2].y()) {
           int temp = p2;
           p2 = p1;
           p1 = temp;
       // y between the points.
       if (y>=quad[p1].y() && y<quad[p2].y() ) {
           float ylength = (quad[p2].y() - quad[p1].y());
           if (ylength==0.0f) ylength = 0.0000001f;    // Prevent division by zero

// Interpolate xedge according y

           xedges[edgecount] = quad[p1].x() + (quad[p2].x() - quad[p1].x()) *
                   ( y-quad[p1].y() ) / ylength;
           if (edgecount==2) break;

// If the coordinate is between left and right edges, it's inside the quad.

   if (edgecount==2) {     // must be 2
       if (xedges[0]<xedges[1]) {
           if (x>=xedges[0] && x<xedges[1]) return true;
       } else {
           if (x>=xedges[1] && x<xedges[0]) return true;
   return false;

} }}}


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