XIMEA, OpenCV and CUDA don't work together as they should

[Honey_Patouceul]

@schirmcharmemelone

      // Render image to the screen (using OpenGL)
      imshow("XIMEA camera", gpu_mat_color);

I think this would only work with GTK2 backend, not QT.
So you may try rebuilding opencv with: -D WITH_GTK=ON -D WITH_GTK_2_X=ON instead of -D WITH_QT=1.
Before this, it would be quicker to confirm this cause just downloading the GpuMat into a CPU Mat and use the latter one for imshow.