I am trying the hello triangle example of OpenGL ES 2.0. I am using Qt, so I created a QGraphicsScene and added that code as a QGraphicsItem. It draws correctly, but I cannot get the bounding rectangle correctly. The triangle vertices are
GLfloat afVertices[] =
{-0.4f,-0.4f,0.0f,
0.4f ,-0.4f,0.0f,
0.0f ,0.4f ,0.0f};
and my viewport is glViewport(0, 0, 800, 480);
What would be the correct bounding rect coordinates?
I set the viewport to a QGLWidget. The thing with the QGraphicsItem is that I have to re-implement the bounding rectangle of the item and if I just use
QRectF myGraphicsItem::boundingRect() const
{
return QGraphicsItem::boundingRect();
}
it says undefined reference to `QGraphicsItem::boundingRect() const'
I had originally used
QRectF myGraphicsItem::boundingRect() const
{
return QRectF(-0.4, -0.4, 0.8, 0.8);
}
but the result is a very small bounding box. The seemingly correct one was created when I was used values like QRectf(300, 200, 200, 200)
by trial and error -which is too 'manual'-, so I was wondering maybe there is some kind of coordinate correspondence or transformation that I'm unaware of.