I'm using Qt5 and its OpenGL integration, and am running into a problem when I try to draw translucent objects. When an object is translucent, whatever is visible behind my OpenGL window is shown within the screen area of that object, instead of the object being blended with whatever is already in the colour buffer. I have started watching YouTube videos through my translucent objects, as whatever shows through is live.
Interestingly, the most see-through an object gets seems to occur at half opacity - full opacity renders it solid, while zero opacity renders nothing at all (and whatever was previously in the background of the 3D scene remains there). Rendering translucent objects last does not fix the issue.
I have noticed that this also happens when I enable mipmaps on my textures - as the distance to a point on an object increases, the pixel concerned becomes more translucent and displays whatever is behind the OpenGL window. The issue occurs both on my Windows and OSX machines.
Is this a known issue? Is there a workaround? Google hasn't proven too helpful.