public void transform_rectangle (ref Rectangle? rect)
rect using this, then calculates the bounding box of the transformed rectangle.
The rectangle should be in Pango units.
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.
If you have a rectangle in device units (pixels), use transform_pixel_rectangle.
If you have the rectangle in Pango units and want to convert to transformed pixel bounding box, it is more accurate to transform it first (using this function) and pass the result to extents_to_pixels, first argument, for an inclusive rounded rectangle. However, there are valid reasons that you may want to convert to pixels first and then transform, for example when the transformed coordinates may overflow in Pango units (large matrix translation for example).
a Matrix, or
in/out bounding box in Pango units, or