Multiple Viewports and resize in QOpenGLWidget

Hi there,
I have a problem drawing multiple viewports on a QOpenGLWidget. Everything seems to work fine until i resize the window (after that the second viewport content disappears forever). Testbed: QT Examples > Qt5.4 > Opengl > cube
changes to code:cpp:
void MainWidget::resizeGL(int w, int h) { this>w = w; this>h = h; // Calculate aspect ratio qreal aspect = qreal(w) / qreal(h ? h : 1); // Set near plane to 3.0, far plane to 7.0, field of view 45 degrees const qreal zNear = 3.0, zFar = 7.0, fov = 45.0; // Reset projection projection.setToIdentity(); // Set perspective projection projection.perspective(fov, aspect, zNear, zFar); cam_projection.perspective(fov, 1.0f, zNear, zFar); } //! [5] void MainWidget::paintGL() { // Clear color and depth buffer glClear(GL_COLOR_BUFFER_BIT  GL_DEPTH_BUFFER_BIT); texture>bind(); //! [6] // Calculate model view transformation QMatrix4x4 matrix; matrix.translate(0.0, 0.0, 5.0); matrix.rotate(rotation); // Set modelviewprojection matrix program.setUniformValue("mvp_matrix", projection * matrix); //! [6] // Use texture unit 0 which contains cube.png program.setUniformValue("texture", 0); // Draw cube geometry geometries>drawCubeGeometry(&program); glViewport(0,0,100,100); // Set modelviewprojection matrix program.setUniformValue("mvp_matrix", cam_projection * matrix); geometries>drawCubeGeometry(&program); glViewport(0,0,w,h); }
add in h:
// new int w,h; QMatrix4x4 cam_projection;
Any Help appreciated,
Regards,
Andrea 
QMatrix4x4::perspective
multiplies the existing matrix by another. In theresetGL()
method the originalprojection
matrix is set to identity before perspective is applied, but you're not doing that for yourcam_projection
, so it gets cumulatively more and more distorted on every resize. Simply addingcam_projection.setToIdentity();
before applying perspective fixes the issue.