| DropShadow |
CSS drop-shadow() (Filter Effects 1 §8.3): “a blurred, offset version of the input image’s alpha mask drawn in a particular colour, composited below the image”. The shadow follows the real alpha shape of what was painted - glyphs, a PNG’s transparent corners, a clipped outline - not its bounding box. |
| FilterOps |
The pixel operations behind the SVG filter primitives that PDF cannot express, on premultiplied RGBA8 surfaces of one size. Each takes its inputs and writes a result of the same size; none keeps state. Geometry-dependent parameters (radii, offsets, scales) arrive already converted to pixels. |
| GaussianBlur |
A Gaussian blur of a premultiplied RGBA8 surface. For a standard deviation of 2 or more it uses the three successive box blurs Filter Effects 1 §feGaussianBlur specifies (which approximate the Gaussian to within a few percent and cost the same regardless of radius); below 2 it convolves with the exact kernel. Everything is integer arithmetic, so the result is identical on every CPU. Pixels outside the surface count as transparent. |
| Turbulence |
Perlin noise exactly as the SVG specification’s reference implementation defines it (Filter Effects 1, feTurbulence), so a given seed, frequency and octave count yields the same picture every conforming renderer draws. |
