ImageFilter

Base class for image filters. If one is installed in the paint, then all drawing occurs as usual, but it is as if the drawing happened into an offscreen (before the xfermode is applied). This offscreen bitmap will then be handed to the imagefilter, who in turn creates a new bitmap which is what will finally be drawn to the device (using the original xfermode).

The local space of image filters matches the local space of the drawn geometry. For instance if there is rotation on the canvas, the blur will be computed along those rotated axes and not in the device space. In order to achieve this result, the actual drawing of the geometry may happen in an unrotated coordinate system so that the filtered image can be computed more easily, and then it will be post transformed to match what would have been produced if the geometry were drawn with the total canvas matrix to begin with.