Use OpenGL 3.2 instead of 3.3 to make MacOSX work again

[davidgraeff]

Fix:

• Move all GL startup calls to GLScope::fixOpenGLversion
• Depending on OpenGL or ES availability initialize the QSurfaceFormat
• Don't crash if the shader compilation failed. Show a nice message instead.
• Use DsoWidget::showEvent to update all kind of UI things. Otherwise for example the zoom view potentially will be "shown" (setVisible), before the DsoWidget finished its constructor and we get multiple initializeGL() calls.

Optimize:

• Don't transfer the marker vertices to the GPU each frame update, only do this if they actually changed position.

Code style:

• LevelSlider: Don't return a value for set* Methods.
• Don't rely on the LevelSliders step to calculate the marker position in the OpenGL view.

Fixes #154 Fixes #155

[Hoagie572]

Hi,

I've tried this and found that with a minor tweak it works on a Raspberry Pi 3. When compiling shaders, in glscope.cpp, I set the coreShaders boolean based on the QT_OPENGL_ES_2 definition and #defined QT_OPENGL_ES_2 at the top of the file.

I'm not sure where QT_OPENGL_ES_2 should normally be defined, there's probably a better place than the top of that file.

I'm using the GL driver on the Pi, which can be enabled in the Advanced Options of the raspi-config application.

Regards, Geoff.

[Hoagie572]

Update: Unsurprisingly, with the Experimental GL driver disabled (the default) it works, but only at about 1 Frame Per Second.