OpenGL 2 renderer

[whitequark]

This is the tracking issue for the OpenGL 2 renderer, being prepared in the opengl2 branch.

There are currently the following problems with the renderer:

• face selection is broken
• display of triangle mesh of solid model is broken
• normals are inverted (?) on Linux/Intel/Mesa graphics stack
• back faces aren't drawn, even when enabled

The Windows builds will use ANGLE; you can check whether they perform well on your configuration by downloading a build from https://ci.appveyor.com/project/whitequark/solvespace/build/3.0.196/artifacts.

[Evil-Spirit]

@whitequark,
1)Evil-Spirit/solvespace@3929a18
2)Evil-Spirit/solvespace@50c773a

[whitequark]

@Evil-Spirit I figured out why I had to do glFrontFace. This is because when we do UpdateProjection(/*flip=*/true), our projection matrix inverts the handedness of the coordinate system. And this worked in OpenGL 1 because it does culling with modelview matrix, and in our case it does culling with modelview*projection matrix.

[whitequark]

@Evil-Spirit I've updated the opengl2 branch. There's one last bug, back faces aren't actually drawn for some reason...

[Evil-Spirit]

@whitequark,
Great. I will look into back faces.

[whitequark]

@Evil-Spirit I've already fixed that actually

[Evil-Spirit]

@whitequark, I mean "back faces aren't drawn, even when enabled"

[whitequark]

@Evil-Spirit Ah yeah, please look into it

[whitequark]

@Evil-Spirit Another problem: on OS X with 3.2 core profile enabled, GL returns 0x502 at the following line in MeshRenderer::Draw:

glEnableVertexAttribArray(ATTRIB_POS);

(and I think all other glEnableVertexAttribArray calls). Do you forget to create the names or something?

[whitequark]

@Evil-Spirit OK I figured it out, GL 3.2+ Core Profile requires VAOs to be used (https://stackoverflow.com/questions/24643027/opengl-invalid-operation-following-glenablevertexattribarray, https://stackoverflow.com/questions/5970087/understanding-vertex-array-objects-glgenvertexarrays). On the other hand, OS X in Compatibility Profile allows only #version 120 shaders to be used.

Wow, what a trash fire...

[Evil-Spirit]

@whitequark,
We are targeting GLES 2.0 - compatible or I miss something?

[whitequark]

@Evil-Spirit We are, but OS X cannot render GLES 2.0, so workarounds are needed. But I have thought up how to do it in only a mildly horrible way.

[Evil-Spirit]

What about Angle for OsX?

[whitequark]

It's possible but I would like to avoid doing all this more complicated than it already is...

[whitequark]

@Evil-Spirit I had to do this hack: https://github.com/solvespace/solvespace/blob/opengl2/src/render/gl2shader.cpp#L63-L87

[Evil-Spirit]

@whitequark,
I think this is not so bad solution.

[whitequark]

@Evil-Spirit I fixed the back face problem. It was because SSurface::TriangulateInto first filled the mesh with triangles with empty color, and then filled the color in separately.

[whitequark]

this is finally MERGED