The commit that changes glBlendFunc to glBlendFuncSeparate fixes an issue that is most evident when running under WSL. e.g. GLVolumeItem example will be see-through such that the contents behind the window will bleed through.
e.g. OpenGL lines with anti-aliasing enabled will also be see-through.

The blend equation SRC_ALPHA * SRC_CHAN + (1 - SRC_ALPHA) * DST_CHAN is not the correct action to perform on the alpha channel. An originally opaque destination pixel blended with a source pixel with transparency will result in a pixel with transparency, which is not the intention.

The following script demonstrates the issue that the last commit is fixing.
This issue is actually present in 0.13.7 and before.

The issue is that the rendering performed by GLScatterPlotItem assumes that blending is enabled. The natively square point is given a circular alpha, which then relies on blending to achieve a circular point.
This is fixed by simply using the discard command at the areas outside the circle.

import numpy as np
import pyqtgraph as pg
import pyqtgraph.opengl as gl

pg.setConfigOptions(background=(128, 128, 128))

pg.mkQApp()
win = gl.GLViewWidget()

pos = np.array([[0, 0, 0]])
item = gl.GLScatterPlotItem(pos=pos, size=10, color=(1.0, 0.0, 0.0, 0.5), pxMode=False)
item.setGLOptions('opaque')

win.addItem(item)
win.show()
pg.exec()

before the fix:

after the fix:

Thanks for your work in this area @pijyoi this looks great.