Add SVG marker, filter, and font-weight/style matching support

README.md

@@ -31,7 +31,8 @@ image operations using `Span<T>`, and supports independent-copy cropping for loa
 - 🖨️ **TIFF Codec** - Load/save 8-bit RGB/RGBA/Grayscale TIFF files
 - 🗜️ **JPEG Codec** - Load baseline/progressive; save baseline JPEG
 - 🎞️ **GIF Codec** - Decode-only load of first GIF frame; `GetInfo` reports the true frame count
-- 📐 **SVG Codec** - Rasterize a common SVG subset to a surface
+- 📐 **SVG Codec** - Rasterize a common SVG subset, including markers/filters and weight/style-aware
+  font matching, to a surface
 - 🔍 **Header-Only Probing** - `GetInfo` reads headers without decoding pixels (GIF excepted)
 - 🖌️ **Path Filling** - Antialiased nonzero/even-odd fill of vector paths
 - 🖊️ **Stroke-to-Fill** - Convert stroked paths into fillable outlines

docs/reqstream/canvas-net.yaml

@@ -963,6 +963,55 @@ sections:
         tests:
           - CanvasNet_SystemIntegration_SvgLoad_ReturnsExpectedPixel
 
+      - id: CanvasNet-Lib-SvgMarkerRendering
+        title: >-
+          The library shall rasterize marker elements referenced from a line, polyline, polygon,
+          or path element's marker-start/marker-mid/marker-end presentation attributes, at the
+          correct vertex, orientation, and scale, and shall reject an unbounded
+          marker-referencing-marker reference cycle the same way an unbounded use reference cycle
+          is already rejected.
+        tags: [system]
+        justification: |
+          Connector arrowheads and other per-vertex line decorations built via SVG's marker
+          mechanism are common in real-world diagrams and flowcharts; callers need these to
+          render rather than silently vanish, with the same bounded, predictable error-handling
+          behavior already established for use reference cycles.
+        children:
+          - CanvasNet-Codecs-SvgMarkerRendering
+        tests:
+          - SvgCodec_Load_MarkerEndOnLine_RendersArrowheadPastLineEnd
+          - SvgCodec_Load_MarkerStartMidEndOnPolyline_RendersDistinctMarkersAtEachVertex
+          - SvgCodec_Load_ArrowMarkersFixture_RendersArrowheadPastLineEnd
+          - SvgCodec_Load_MarkerSelfReferenceCycle_ThrowsInvalidDataException
+          - SvgCodec_Load_MarkerTwoElementReferenceCycle_ThrowsInvalidDataException
+
+      - id: CanvasNet-Lib-SvgFilterRendering
+        title: >-
+          The library shall rasterize filter elements referenced from any directly renderable
+          shape or text element's filter presentation attribute, evaluating a
+          feFlood/feGaussianBlur/feOffset/feComposite/feMerge primitive chain against that
+          element's own content within a bounded-size temporary offscreen surface, and shall
+          tolerate a dangling filter reference, an unsupported primitive type, and a
+          pathologically large filter region or blur radius without failing or hanging.
+        tags: [system]
+        justification: |
+          Solid-color halo/glow backgrounds behind text labels, built via SVG's filter
+          mechanism, are common in real-world diagrams (the reported real-world bug this feature
+          fixes: SvgRenderer's own midpoint line labels use exactly this pattern, and previously
+          lost their halo entirely, causing label text to overlap the line beneath it); callers
+          need this common pattern to render rather than silently vanish, with the same bounded,
+          predictable resource-safety behavior already established for this codec's other
+          reference-following and work-budget concerns.
+        children:
+          - CanvasNet-Codecs-SvgFilterRendering
+        tests:
+          - SvgCodec_Load_FeFloodFilter_RendersSolidColorBehindElement
+          - SvgCodec_Load_FeFloodFeGaussianBlurFeCompositeFilter_RendersBlurredHaloBehindContent
+          - SvgCodec_Load_LabelHaloFixture_RendersWhiteHaloBehindLineMidpointLabel
+          - SvgCodec_Load_FilterDanglingReference_RendersElementNormally
+          - SvgCodec_Load_FilterPathologicallyLargeRegion_SkipsFilterRatherThanUnboundedAllocation
+          - SvgCodec_Load_FilterPathologicallyLargeBlurStdDeviation_ClampsRatherThanUnboundedWork
+
       - id: CanvasNet-Lib-SvgViewBoxFitting
         title: >-
           The library shall fit an SVG document's intrinsic viewBox into the requested raster size
@@ -1017,6 +1066,28 @@ sections:
           - SvgCodec_Load_TextFontFamilyNoMatch_SkipsSilentlyWithoutThrowing
           - SvgCodec_Load_TextFontFamilyCommaSeparatedList_MatchesFirstAvailableFont
 
+      - id: CanvasNet-Lib-SvgFontWeightStyleMatching
+        title: >-
+          The library shall register more than one font face (varying in font-weight/font-style)
+          per SVG text font-family and select the closest-matching registered face for each text
+          element's own cascaded font-weight/font-style, while preserving the pre-existing
+          single-font-per-family Load overload's behavior unchanged.
+        tags: [system]
+        justification: |
+          Callers commonly need bold titles and italic keywords rendered with the correct
+          distinct font face, rather than every element in a family always resolving to the
+          same single font regardless of its requested weight/style; existing callers of the
+          single-font-per-family overload must observe no behavior change.
+        children:
+          - CanvasNet-Codecs-SvgFontWeightStyleMatching
+        tests:
+          - SvgCodec_Load_TextFontWeightBold_SelectsBoldFaceOverNormalFace
+          - SvgCodec_Load_TextFontStyleItalic_SelectsItalicFaceOverNormalFace
+          - SvgCodec_Load_TextFontWeightAndStyleCombined_SelectsExactMatchAmongThreeFaces
+          - SvgCodec_Load_GroupFontWeightInheritance_AppliesToChildTextWithoutOwnFontWeight
+          - SvgCodec_Load_GroupFontStyleInheritance_AppliesToChildTextWithoutOwnFontStyle
+          - SvgCodec_Load_TextLegacySingleFontOverload_IgnoresRequestedWeightAndStyle
+
       - id: CanvasNet-Lib-SvgValidationNull
         title: >-
           The library shall reject null stream/path arguments to SVG Load and GetInfo operations

docs/reqstream/canvas-net/codecs.yaml

@@ -925,6 +925,55 @@ sections:
               - CanvasNet_SystemIntegration_SvgLoad_ReturnsExpectedPixel
               - SvgCodec_Load_NonPositiveWidth_PropagatesSurfaceArgumentOutOfRangeException
 
+          - id: CanvasNet-Codecs-SvgMarkerRendering
+            title: >-
+              The Codecs subsystem shall rasterize marker elements referenced from a line,
+              polyline, polygon, or path element's marker-start/marker-mid/marker-end
+              presentation attributes, at the correct vertex, orientation, and scale, and shall
+              reject an unbounded marker-referencing-marker reference cycle the same way an
+              unbounded use reference cycle is already rejected.
+            justification: |
+              Connector arrowheads and other per-vertex line decorations built via SVG's marker
+              mechanism are common in real-world diagrams and flowcharts; callers need these to
+              render rather than silently vanish, with the same bounded, predictable
+              error-handling behavior already established for use reference cycles.
+            children:
+              - CanvasNet-Codecs-SvgCodec-MarkerRendering
+              - CanvasNet-Codecs-SvgCodec-MarkerReferenceCycle
+            tests:
+              - SvgCodec_Load_MarkerEndOnLine_RendersArrowheadPastLineEnd
+              - SvgCodec_Load_MarkerStartMidEndOnPolyline_RendersDistinctMarkersAtEachVertex
+              - SvgCodec_Load_ArrowMarkersFixture_RendersArrowheadPastLineEnd
+              - SvgCodec_Load_MarkerSelfReferenceCycle_ThrowsInvalidDataException
+              - SvgCodec_Load_MarkerTwoElementReferenceCycle_ThrowsInvalidDataException
+
+          - id: CanvasNet-Codecs-SvgFilterRendering
+            title: >-
+              The Codecs subsystem shall rasterize filter elements referenced from any directly
+              renderable shape or text element's filter presentation attribute, evaluating a
+              feFlood/feGaussianBlur/feOffset/feComposite/feMerge primitive chain against that
+              element's own content within a bounded-size temporary offscreen surface, and shall
+              tolerate a dangling filter reference, an unsupported primitive type, and a
+              pathologically large filter region or blur radius without failing or hanging.
+            justification: |
+              Solid-color halo/glow backgrounds behind text labels, built via SVG's filter
+              mechanism, are common in real-world diagrams (the reported real-world bug this
+              feature fixes: SvgRenderer's own midpoint line labels use exactly this pattern, and
+              previously lost their halo entirely, causing label text to overlap the line
+              beneath it); callers need this common pattern to render rather than silently
+              vanish, with the same bounded, predictable resource-safety behavior already
+              established for this codec's other reference-following and work-budget concerns.
+            children:
+              - CanvasNet-Codecs-SvgCodec-FilterRendering
+              - CanvasNet-Codecs-SvgCodec-FilterResourceSafety
+            tests:
+              - SvgCodec_Load_FeFloodFilter_RendersSolidColorBehindElement
+              - SvgCodec_Load_FeFloodFeGaussianBlurFeCompositeFilter_RendersBlurredHaloBehindContent
+              - SvgCodec_Load_LabelHaloFixture_RendersWhiteHaloBehindLineMidpointLabel
+              - SvgCodec_Load_FilterDanglingReference_RendersElementNormally
+              - SvgCodec_Load_FilterPathologicallyLargeRegion_SkipsFilterRatherThanUnboundedAllocation
+              - SvgCodec_Load_FilterPathologicallyLargeBlurStdDeviation_ClampsRatherThanUnboundedWork
+
           - id: CanvasNet-Codecs-SvgViewBoxFitting
             title: >-
               The Codecs subsystem shall fit an SVG document's intrinsic viewBox into the
@@ -982,6 +1031,30 @@ sections:
               - SvgCodec_Load_TextFontFamilyNoMatch_SkipsSilentlyWithoutThrowing
               - SvgCodec_Load_TextFontFamilyCommaSeparatedList_MatchesFirstAvailableFont
 
+          - id: CanvasNet-Codecs-SvgFontWeightStyleMatching
+            title: >-
+              The Codecs subsystem shall register more than one font face (varying in
+              font-weight/font-style) per SVG text font-family and select the closest-matching
+              registered face for each text element's own cascaded font-weight/font-style,
+              while preserving the pre-existing single-font-per-family Load overload's behavior
+              unchanged.
+            justification: |
+              Callers commonly need bold titles and italic keywords rendered with the correct
+              distinct font face, rather than every element in a family always resolving to the
+              same single font regardless of its requested weight/style; existing callers of the
+              single-font-per-family overload must observe no behavior change.
+            children:
+              - CanvasNet-Codecs-SvgCodec-FontWeightStyleCascade
+              - CanvasNet-Codecs-SvgCodec-FontFaceMatching
+              - CanvasNet-Codecs-SvgCodec-LegacySingleFontCompatibility
+            tests:
+              - SvgCodec_Load_TextFontWeightBold_SelectsBoldFaceOverNormalFace
+              - SvgCodec_Load_TextFontStyleItalic_SelectsItalicFaceOverNormalFace
+              - SvgCodec_Load_TextFontWeightAndStyleCombined_SelectsExactMatchAmongThreeFaces
+              - SvgCodec_Load_GroupFontWeightInheritance_AppliesToChildTextWithoutOwnFontWeight
+              - SvgCodec_Load_GroupFontStyleInheritance_AppliesToChildTextWithoutOwnFontStyle
+              - SvgCodec_Load_TextLegacySingleFontOverload_IgnoresRequestedWeightAndStyle
+
           - id: CanvasNet-Codecs-SvgValidationNull
             title: >-
               The Codecs subsystem shall reject null stream/path arguments to SVG Load and