Implement more filter effects

[Herschel]

Currently Pathfinder only supports blur. Pathfinder could support more of the filters from the SVG spec: https://www.w3.org/TR/SVG11/filters.html

Additionally, it'd be useful to support multiple filters simultaneously; currently Pattern only allows for a single filter. As a separate use case, Flash content allows for a color transform to be applied to any shape (mult * inColor + add) as well as various filter effects, such as blur and drop shadow. Multiple filters can be applied to a single object.

[pcwalton]

Which filters does Flash need that aren't already implemented?

[Herschel]

Here's a list of all the filter effects Flash supports, along with the SVG counterpart:

• BlurFilter (feGaussianBlur)
• ColorMatrixFilter (feColorMatrix)
• ConvolutionFilter (feConvolveMatrix)
• DisplacementMapFilter (feDisplacementMap)
• DropShadowFilter (feOffset, feGaussianBlur and friends)
• GlowFilter (feGaussianBlur and friends)
• BevelFilter (feDiffuseLighting and friends?)
• GradientBevelFilter
• GradientGlowFilter (source: https://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/filters/package-detail.html) Blur, drop shadow, and glow are the most common. Some of the above would require a combination of several SVG effects.

The most important are color transforms, which were not technically a filter in Flash land and exist in most Flash content. These could be implemented using feColorMatrix.

[pcwalton]

536cb4c0936cac9d3dcb03bee22335d8b5df257d implements color matrix.