def paintEvent(self, event):
        """ A custom paint event handler which draws the image according
        to the current size constraints.

        """
        pixmap = self._pixmap
        if pixmap is None:
            return

        pm_size = pixmap.size()
        pm_width = pm_size.width()
        pm_height = pm_size.height()
        if pm_width == 0 or pm_height == 0:
            return

        width = self.size().width()
        height = self.size().height()

        if not self._scaled_contents:
            # If the image isn't scaled, it is centered if possible.
            # Otherwise, it's painted at the origin and clipped.
            paint_x = max(0, int(width / 2. - pm_width / 2.))
            paint_y = max(0, int(height / 2. - pm_height / 2.))
            paint_width = pm_width
            paint_height = pm_height
        else:
            # If the image *is* scaled, it's scaled size depends on the
            # size of the paint area as well as the other scaling flags.
            if self._preserve_aspect_ratio:
                pm_ratio = float(pm_width) / pm_height
                ratio = float(width) / height
                if ratio >= pm_ratio:
                    if self._allow_upscaling:
                        paint_height = height
                    else:
                        paint_height = min(pm_height, height)
                    paint_width = int(paint_height * pm_ratio)
                else:
                    if self._allow_upscaling:
                        paint_width = width
                    else:
                        paint_width = min(pm_width, width)
                    paint_height = int(paint_width / pm_ratio)
            else:
                if self._allow_upscaling:
                    paint_height = height
                    paint_width = width
                else:
                    paint_height = min(pm_height, height)
                    paint_width = min(pm_width, width)
            # In all cases of scaling, we know that the scaled image is
            # no larger than the paint area, and can thus be centered.
            paint_x = int(width / 2. - paint_width / 2.)
            paint_y = int(height / 2. - paint_height / 2.)

        # Finally, draw the pixmap into the calculated rect.
        painter = QPainter(self)
        painter.setRenderHint(QPainter.SmoothPixmapTransform)
        painter.drawPixmap(paint_x, paint_y, paint_width, paint_height, pixmap)

    #--------------------------------------------------------------------------
    # Public API
    #--------------------------------------------------------------------------
dataset/ETHPy150Open enthought/traitsui/traitsui/qt4/image_editor.py/QImageView.paintEvent/original