def render_image(self, rect, image_path, dpm, quality, bg_color, autocrop):
"""Render a section of self.scene to an image.
It is assumed that all input arguments are valid.
Args:
rect (Rect): The part of the document to render,
in document coordinates.
image_path (str): The path to the output image.
This must be a valid path relative to the current
working directory.
dpm (int): The pixels per meter of the rendered image.
quality (int): The quality of the output image for compressed
image formats. Must be either `-1` (default compression) or
between `0` (most compressed) and `100` (least compressed).
bg_color (Color): The background color for the image.
autocrop (bool): Whether or not to crop the output image to tightly
fit the contents of the frame. If true, the image will be
cropped such that all 4 edges have at least one pixel not of
`bg_color`.
Returns: None
Raises:
ImageExportError: If Qt image export fails for unknown reasons.
"""
scale_factor = dpm / Unit(Meter(1)).value
pix_width = Unit(rect.width).value * scale_factor
pix_height = Unit(rect.height).value * scale_factor
q_image = QtGui.QImage(pix_width, pix_height,
QtGui.QImage.Format_ARGB32)
q_image.setDotsPerMeterX(dpm)
q_image.setDotsPerMeterY(dpm)
q_color = color_to_q_color(bg_color)
q_image.fill(q_color)
painter = QtGui.QPainter()
painter.begin(q_image)
target_rect = QtCore.QRectF(q_image.rect())
source_rect = rect_to_qt_rect_f(rect)
self.scene.render(painter, target=target_rect, source=source_rect)
painter.end()
if autocrop:
q_image = images.autocrop(q_image, q_color)
success = q_image.save(image_path, quality=quality)
if not success:
raise ImageExportError(
'Unknown error occurred when exporting image to ' + image_path)
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