no OpenGL experts on the list? > On Dec 5, 2019, at 5:21 PM, David M. Cotter <d...@kjams.com> wrote: > > 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: > > <qwidget.png> > > 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: > > <qoglwidget.png> > > 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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