preRender.py 文件源码

def renderTile(tx, ty, zoom, polygons, borders = True, width = 256, height = 256):
    """
    renderTile -- return a numpy array of uint32

    tx -- tile x coord
    ty -- tile y coord
    zoom -- tile zoom
    polygon -- a polygon locator
    """
    # FORMAT_ARGB32 is premultiplied, which results in loss of precision and thus cannot be used.
    # FORMAT_RGB30 offers up 30bits, (1 billion uniques), 
    #               but isn't available until 1.12 (we have 1.10)
    # FORMAT_RGB24 will have to be used.
    # Another option would be to render a 2nd channel with the alpha info.
    #borders = False
    surface = cairo.ImageSurface(cairo.FORMAT_RGB24, width, height)
    ctx = getContext(surface, tx, ty, zoom)
    bsurface = cairo.ImageSurface(cairo.FORMAT_RGB24, width, height)
    ctx2 = getContext(bsurface, tx, ty, zoom)
    simple_level = zoom if zoom < 10 else -1
    extents = ctx.clip_extents()
    for pid in polygons.overlapping(extents):
        polygon = polygons.source.get(pid)
        if simple_level > -1:
            polygon = simple(polygon, zoom)
        drawPoly(ctx, ctx2, polygon, pid)
    #if borders:
    #    for width in range(10,0,-1):
    #        ctx2.set_source_rgb(0.0,0.0,width/256.)
    #        width = width/ctx2.get_matrix()[0]
    #        ctx2.set_line_width(width)
    #        ctx2.stroke_preserve()
    surface.flush() #make sure operations are finished
    #surface.write_to_png ("example.png") # Output to PNG
    a = numpy.frombuffer(surface.get_data(), 'uint32') & 0x00ffffff
    surface.finish()
    if borders:
        bsurface.flush()
        b = numpy.frombuffer(bsurface.get_data(), 'uint32') & 0x00ffffff
        #bsurface.write_to_png ("example2.png") # Output to PNG
        bsurface.finish()
        return a,b
    # get_data returns buffer
    # FORMAT_RGB24 consists of 32bit pixel in system byteorder
    # as A,R,G,B values.
    # The Alpha channel is present but unused, however
    # it still contains data and must be zeroed.
    return a,None