Add possibility to see the interior of the model using cutting plane

[knoppix2]

Add possibility to see the interior of the model using cutting plane

• New menu entry: Enable cutting plane

• New menu entry: Wheel mode. The wheel can act as zoom control or for
  moving the cutting plane.
  Alternatively one can press Ctrl modifier to make a Wheel controlling
  a cutting plane.

• Pressing Ctrl modifier and a left mouse button rotates a cutting plane.

• Minimal GLSL version for mesh.vert shader is bumped to 140, as
  glClipPlane is deprecated and the similar shader functionality
  was added in GLSL version 1.40

[sur5r]

Nice feature.

I'm a bit unsure about the choice of the middle mouse button, though. While this is convenient for a desktop machine running Linux or Windows, it's less ideal on most notebooks and impossible on macOS where that concept doesn't exist at all.

Maybe a modifier button is a better approach here.

Don't get me wrong please: I'm a big fan of the three button mouse, but reality of hardware produced forces us elsewhere.

[knoppix2]

Maybe a modifier button is a better approach here.

Don't get me wrong please: I'm a big fan of the three button mouse, but reality of hardware produced forces us elsewhere.

Yeah, you're right. I choose a Ctrl as a modifier. At the same way it controls a role of a Wheel (see updated commit of MR).

And other question, with this modification some old devices with GLES2 will not work anymore. Should I add the check for the GL_EXT_clipping_plane extension enabled or it's ok to leave it as is?

[ptsouchlos]

Sorry for the delay. I gave this a try and with larger models, when the cutting plane is enabled, the model disappears for me when moving it. Can you replicate this behavior @knoppix2?

[knoppix2]

@ptsouchlos no problem :) I think the code still need a better refactoring to be included. Could you post an example that triggers the bug?

[ptsouchlos]

@ptsouchlos no problem :) I think the code still need a better refactoring to be included. Could you post an example that triggers the bug?

Sounds good.

I no longer have the file on hand, but I just found a large STL file online. You could also use the one linked to in the README (Eifel tower). If you have trouble reproducing the issue let me know.

[knoppix2]

I tried it with eiffel.stl and can not reproduce the bug. Could you describe the steps exactly?

[ptsouchlos]

I tried it with eiffel.stl and can not reproduce the bug. Could you describe the steps exactly?

Ok thanks. I'll try again and will record the steps.