Reference document: http://docs.gl/gl3/glPushAttrib
This patch only tackles the bits that are set by Blender with the
following exceptions:
1) Deprecated states (e.g., GL_STIPPLE) are not saved/restored
2) The exception being GL_ALPHA_TEST, which will be removed, but it may
affect drawing too much now. To be removed once we no longer set GL_ALPHA_TEST
elsewhere.
3) paint_cursor will be tackled separated, since it was abusing
glPush/PopAttrib in the first place.
4) Despite what the glPushAttrib page above may suggest, GL_DEPTH_WRITEMASK needs glGet, not glIsEnabled
5) BGE is still a problem since it relies on GL_ALL_ATTRIB_BITS which
would lead to a way more complete/lenghty solution. Since the BGE has
other (OpenGL deprecated) problems anyways, it can be handled on its own
time.
Finally, the original design for 2.8 was to implement a proper stack
system. However we need to move to core profile sooner than later. So
this is a pragmatic temporary (that may be permanent) solution.
Reviewers: merwin, campbellbarton
Differential Revision: https://developer.blender.org/D2600
Intended to replace legacy GL_SELECT, without the limitations of
sample queries which can't access depth information.
This commit adds VIEW3D_SELECT_PICK_NEAREST and VIEW3D_SELECT_PICK_ALL
which access the depth buffers to detect whats under the pointer,
so initial selection is always the closest item.
The performance of this method depends a lot on the OpenGL
implementations glReadPixels.
Since reading depth can be slow, buffers are cached for object picking
so selecting re-uses depth data, performing 1 draw instead of 3
(for 24, 18, 10 px regions, picking with many items under the pointer).
Occlusion queries draw twice when picking nearest,
so worst case 6x draw calls per selection.
Even with these improvements occlusion queries is faster on AMD hardware.
Depth selection is disabled by default, toggle option under select method.
May enable by default if this works well on different hardware.
Reviewed as D2543
