Painter: transform coordinates but not pen width settings

[SixDegrees]

First, a pen of width 0 is always drawn at the same (1-pixel) width.

Second, you could apply the transform to the painter, then apply its inverse to the pen. Not exactly sure how to proceed with that idea, but the basic idea is to scale the pen width back to what it started out as.

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Or, simply store the "fixed" pen size, apply the transform to the painter, then set the pen width to the stored value.