[Interest] QOpenGLWidget strokes premul, while QWidget is straight?

[David M. Cotter]

referring to this article <https://forum.qt.io/topic/5327/how-to-use-semi-transparent-qpixmaps-as-textures>, i see someone else has also run into this, but did not get a satisfactory answer.

I am implementing what on macOS Carbon is known as a "transparency layer", that is, you begin a transparency context, do your drawing (with transparency), finish your context, then blit the contents of that context as a whole with a specified transparency (this is to achieve "fade away" via animation).

When i use QWidget, my stroked paths (text) look creamy smooth along the edges, as if everything is in fact being handled as straight alpha:


However, if i switch to using QOpenGLWidget, my stroked paths appear to have a crusty border, as if they were drawn with premul-over-black alpha:


No other code changes except swapping QOpenGLWidget for QWidget.

Does this seem... unexpected? Note if i attempt to manually unmultiply, things look much worse, so i don't think it's PRECISELY a premul thing. (and i know my manual unmultiply works because unit tests)

(Ignore for now the fact that it's white-on-white, i know that, i'm NOT drawing the black text behind the stroke to more clearly illustrate the halo around the strokes)

-dave
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