Created
January 16, 2022 01:49
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create a bitmap mask from a shapely polygon
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| import numpy | |
| import cairo | |
| def polygon_mask(polygon): | |
| assert polygon.geom_type == 'Polygon' | |
| minx, miny, maxx, maxy = polygon.bounds | |
| minx, miny = numpy.floor([minx, miny]).astype(numpy.int32) | |
| maxx, maxy = numpy.ceil([maxx, maxy]).astype(numpy.int32) | |
| w = int(maxx - minx) | |
| h = int(maxy - miny) | |
| pts = list(polygon.exterior.coords) - numpy.array([minx, miny]) | |
| with cairo.ImageSurface(cairo.FORMAT_ARGB32, w, h) as surface: | |
| ctx = cairo.Context(surface) | |
| ctx.move_to(*pts[0]) | |
| for p in pts[1:]: | |
| ctx.line_to(*p) | |
| ctx.set_source_rgb(1, 1, 1) | |
| ctx.fill() | |
| surface.finish() | |
| data = numpy.ndarray( | |
| shape=(surface.get_height(), surface.get_stride() // 4), | |
| dtype=numpy.uint32, | |
| buffer=surface.get_data()) | |
| data = numpy.right_shift(data, 24).astype(numpy.uint8) | |
| return data > 0, (minx, miny, w, h) |
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