如何使用Python应用alpha掩码'；s svgwrite模块？

我正在使用该模块以编程方式为项目创建一些图像。我需要使用alpha遮罩来创建渐变透明元素。我不清楚如何实际应用一个面具一旦被创建

在下面的示例中，我尝试使用圆形渐变在灰色正方形中创建渐变透明环。我可以创造广场；我可以分别创建圆形渐变def和一个填充它的圆形

把一个当作面具用在另一个身上我不明白

def my_mask():
            #  define some params
            width = "500px"
            height = "500px"
            radius = "50%"
            black = "rgb(255, 255, 255)"
            grey = "rgb(127,127,127)"

            #  create the drawing surface
            canvas = svgwrite.Drawing('temp_mask.svg', (width, height))

            #  create defs, in this case, just a single gradient
            rad_grad = canvas.radialGradient(("50%", "50%"), "50%", ("50%", "50%"), id="rad_grad")
            rad_grad.add_stop_color("0%", black, 0)
            rad_grad.add_stop_color("66.6%", black, 255)
            rad_grad.add_stop_color("100%", black, 255)

            #  now to draw; first I create the rect object to be masked
            base_rect = canvas.rect( (0, 0), (width, height), id="masked_rect").fill(grey)
            canvas.add(base)
    
            #  and according to the docs, any SVG fragment can be an alpha mask, so I create this circle
            mask_element = canvas.circle((radius, radius), radius, fill="url(#rad_grad)")

            #  but here's where I get confused; I don't get how this function actually makes use of one element to mask another
            canvas.mask((0, 0), (width, height))

        #  No problem exporting to a file, though. :)
        canvas.save()

以下是我想要的（红十字会刚刚加入以显示透明度）；易于绘制草图

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我怀疑这是一个不雅观的或至少是非常冗长的解决方案，但是，在又花了一个小时到处玩之后，我想出的一般解决方案是：

1） 在SVG defs中定义掩码 2） 将SVG对象添加到所述遮罩以创建alpha贴图 3） 可以预见，在遮罩对象的遮罩属性中引用遮罩：

注意：我的渐变中也有错误的值，因此它们永远不会生成我包含的图像；下面的代码也解决了这个问题

def my_mask():
            #  define some params
            width = "500px"
            height = "500px"
            radius = "50%"
            white = "rgb(255, 255, 255)"
            black = "rgb(0, 0, 0)"
            grey = "rgb(127,127,127)"

            #  create the drawing surface
            canvas = svgwrite.Drawing('temp_mask.svg', (width, height))

            #  create defs, in this case, just a single gradient
            rad_grad = canvas.radialGradient(("50%", "50%"), "50%", ("50%", "50%"), id="rad_grad")
            rad_grad.add_stop_color("0%", black, 0)
            rad_grad.add_stop_color("66.6%", white, 255)
            rad_grad.add_stop_color("100%", white, 255)
            canvas.defs.add(rad_grad)

            #  create the mask container as a def and include alpha-mapping objects
            mask = canvas.mask((0, 0), (width, height), id="grad_mask")
            mask.add(canvas.rect( (0, 0), (width, height) ).fill(white)
            mask.add(canvas.circle((radius, radius), radius, fill="url(#rad_grad)")
            canvas.defs.add(mask)

            #  now to draw; create the rect object and simply include the mask as an attribute
            base_rect = canvas.rect( (0, 0), (width, height), mask="url(#grad_mask)".fill(grey)
            canvas.add(base)

            #  Still no problem exporting to a file, though. ;)
            canvas.save()

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谢谢Jonline！ClipPath和Mask的svgwrite“示例”没有实际演示如何将其应用于图形。为了完整起见，我使用您的方法为ClipPath编写了一个真实的示例：

clip_path=dwg.defs.add（dwg.clipPath（id='my_clip_path1'））#命名剪辑路径
剪辑_path.add（dwg.circle（（5*mm，5*mm，10*mm））35;将绘制此形状内的内容
testCircle=dwg.add（dwg.g（id='test'，stroke='red'，stroke_width=1，fill='black'，fill_opacity=1，clip_path=“url（#my_clip_path1）”）
testCircle.add（dwg.circle（（5*mm，10*mm，10*mm））