Depth testing was off as it used the precomputed ModelView matrix. As draw engines currently use a different approach the depth was sometimes a bit off making the color disappear. This change will use a different vertex shader that will write the correct depth. I expected the same change to be needed in the bone selection overlay but was not able to reproduce it. Reviewed By: fclem Maniphest Tasks: T64615 Differential Revision: https://developer.blender.org/D5006