Matrix.transformPixelRectangle

First transforms the rect using matrix, then calculates the bounding box of the transformed rectangle.

This function is useful for example when you want to draw a rotated PangoLayout to an image buffer, and want to know how large the image should be and how much you should shift the layout when rendering.

For better accuracy, you should use [pango.matrix.Matrix.transformRectangle] on original rectangle in Pango units and convert to pixels afterward using funcextents_to_pixels's first argument.