SVG: filters

renderSVG applies filters: url(#...) and the filter functions (blur,
drop-shadow, brightness, contrast, grayscale, hue-rotate, invert,
opacity, saturate, sepia). New src/render/filter.ts, ported from resvg:
8 bit premultiplied pixels like resvg's (its rounding, the linearRGB
tables as the rounded curves), feGaussianBlur (box blur from sigma 2,
IIR below), feOffset, feFlood, feComposite (arithmetic too), feMerge,
feDropShadow, feColorMatrix, feComponentTransfer, feTile, feBlend
(tiny-skia's 16 modes), feMorphology (separable, monotonic queue: linear
time, 80 s -> 0.1 s for resvg's huge-radius test), feConvolveMatrix.
svg.ts parses filters like usvg: regions and subregions in both units,
attributes through href, inputs/results, color-interpolation-filters,
invalid filters hide the element (invalid convolutions are transparent);
filters with feImage, feTurbulence, feDisplacementMap or lighting are
left out. An element with filters renders into a layer covering the
filter regions in its scale (2 canvases of margin, like resvg), rotation
and skew applied when drawn (bilinear). Scales are tiny-skia's get_scale
(the rows' lengths), now for pattern tiles too. Filter attributes are
plain numbers (10% isn't 0.1 there).

resvg's filter tests: 300/408 (was 81; blur, offset, flood, composite,
merge, color matrix, component transfer, blend, morphology, convolve all
pass; the rest is mostly the unsupported primitives), copied to
tests/svgs/resvg (1 MB); tests/svg.js takes 21 s instead of 5 s.
Patterns 32/33, markers 61/64, images 17/56 unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lfv41PqHEGbU7SLg5onpG1

Author: matmen

CHANGELOG.md

@@ -26,6 +26,15 @@
   loaded. Elements of embedded SVGs count towards the limit of 100000 elements rendered through references. Of
   resvg's 56 image tests, 17 pass the test suite's threshold, 37 without the frame around them, whose antialiasing
   differs (tiny-skia rounds edges to quarter pixels); most of the others load files.
+- `Image.renderSVG()` applies filters (`filter="url(#…)"` and the filter functions `blur()`, `drop-shadow()`,
+  `brightness()`, `contrast()`, `grayscale()`, `hue-rotate()`, `invert()`, `opacity()`, `saturate()`, `sepia()`):
+  feGaussianBlur, feOffset, feFlood, feComposite (with `arithmetic`), feMerge, feDropShadow, feColorMatrix,
+  feComponentTransfer, feTile, feBlend (all 16 modes), feMorphology and feConvolveMatrix, with filter regions and
+  subregions in both units, `color-interpolation-filters` (linear RGB by default), inputs and results, attributes
+  through `href`. Like resvg (ported from it), filters run on 8 bit premultiplied pixels in the element's scale,
+  rotation and skew applied afterwards; invalid filters hide the element. Filters with feImage, feTurbulence,
+  feDisplacementMap or lighting aren't applied (the element is drawn without them). 300 of resvg's 408 filter tests
+  pass, up from 81 (most others use the primitives that aren't supported).
 - Optimized lossy WebP animations are smaller: like libwebp's, they leave out pixels that changed by up to a tolerance
   from the quality (3 per channel at quality 85, 1 at 100), and make unchanged pixels transparent only in whole 8x8
   blocks. Making each unchanged pixel transparent gave speckled alpha masks where most pixels change a little

README.md

@@ -54,7 +54,7 @@ encode as GIF, APNG or WebP.
 
 - [Text rendering](https://imagescript.matmen.dev/classes/Image.html#rendertext) with TrueType and OpenType fonts,
   in every script, with color emoji
-- [SVG rendering](https://imagescript.matmen.dev/classes/Image.html#rendersvg) (no text or filters)
+- [SVG rendering](https://imagescript.matmen.dev/classes/Image.html#rendersvg) (no text)
 - [Resizing](https://imagescript.matmen.dev/classes/Image.html#resize),
   [cropping](https://imagescript.matmen.dev/classes/Image.html#crop),
   [rotating](https://imagescript.matmen.dev/classes/Image.html#rotate),

THIRD_PARTY_NOTICES.md

@@ -25,7 +25,9 @@ following projects, under their own licenses. Each derived file says so in its h
 | [Pillow](https://github.com/python-pillow/Pillow) | `src/util/resample.ts` (filter coefficients, box, bilinear and bicubic filters) | MIT-CMU |
 | [HarfBuzz](https://github.com/harfbuzz/harfbuzz) | `src/render/buffer.ts`, `src/render/layout.ts`, `src/render/shape.ts`, `src/render/shapers/*` (OpenType shaping: buffer, GSUB/GPOS, normalization, fallback positioning, the script shapers and syllable grammars), `scripts/unicode.js` (shaping category tables) | Old MIT |
 | [Universal Shaping Engine data](https://github.com/harfbuzz/harfbuzz/tree/main/src/ms-use) by Microsoft | `scripts/ms-use` (category overrides, invalid vowel sequences), the tables generated from them in `src/render/unicode-data.ts` | MIT |
-| [resvg](https://github.com/linebender/resvg) by the Resvg Authors | `src/render/svg.ts` (how patterns are rendered and their reference cycles broken, following resvg and usvg; the markers' placement and orientation, ported from usvg; as many cubics per arc as kurbo makes for usvg; how images are fitted, clipped and sampled), `tests/svgs/resvg` (test cases with resvg's renderings) | MIT (or Apache-2.0) |
+| [resvg](https://github.com/linebender/resvg) by the Resvg Authors | `src/render/filter.ts` (the filter effects: regions, inputs, color spaces, box blur (based on [fastblur](https://github.com/fschutt/fastblur)), IIR blur, offset, flood, composite, merge, drop shadow, color matrix, component transfer, tile, morphology, convolution), `src/render/svg.ts` (the filters' attributes like usvg; how patterns are rendered and their reference cycles broken, following resvg and usvg; the markers' placement and orientation, ported from usvg; as many cubics per arc as kurbo makes for usvg; how images are fitted, clipped and sampled), `tests/svgs/resvg` (test cases with resvg's renderings) | MIT (or Apache-2.0) |
+| [tiny-skia](https://github.com/linebender/tiny-skia) by Yevhenii Reizner (from [Skia](https://skia.org) by Google) | `src/render/filter.ts` (feBlend's blend modes) | BSD-3-Clause |
+| [gaussianiir](http://www.getreuer.info/home/gaussianiir) by Pascal Getreuer | `src/render/filter.ts` (the IIR blur for small deviations, through resvg) | BSD-2-Clause (Simplified BSD) |
 | [Unicode Character Database](https://www.unicode.org/ucd/) | `src/render/unicode-data.ts` (character properties, generated by `scripts/unicode.js`) | Unicode License v3 |
 
 ## fflate, Fast CRC32 in JavaScript
@@ -520,3 +522,69 @@ OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
 IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.
 ```
+
+## tiny-skia
+
+```
+Copyright (c) 2011 Google Inc. All rights reserved.
+Copyright (c) 2020 Yevhenii Reizner All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+  * Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+
+  * Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in
+    the documentation and/or other materials provided with the
+    distribution.
+
+  * Neither the name of the copyright holder nor the names of its
+    contributors may be used to endorse or promote products derived
+    from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+```
+
+## gaussianiir
+
+The IIR blur follows Pascal Getreuer's gaussianiir (through resvg), under the Simplified BSD License:
+
+```
+Copyright (c) 2009, Pascal Getreuer
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in
+      the documentation and/or other materials provided with the distribution
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+```

src/image.ts

@@ -2260,7 +2260,8 @@ export class Image {
     /**
      * Creates a new image from the given SVG
      * Supports shapes, paths, transforms, use/symbol, CSS styles, gradients, patterns, strokes, markers, clip paths,
-     * masks, opacity and images embedded as data URIs (PNG, JPEG, GIF, WebP, SVG); text and filters are not rendered
+     * masks, opacity, filters (most primitives and the filter functions) and images embedded as data URIs (PNG, JPEG,
+     * GIF, WebP, SVG); text is not rendered
      * @param svg The SVG content
      * @param options See {@link SVGOptions}
      * @return The rendered SVG graphic