C API: add optional Skrifa draw and paint features

.github/workflows/main.yml

@@ -108,6 +108,39 @@ jobs:
     - name: Rustfmt
       run: cargo fmt --all -- --check
 
+    - name: Draw and paint C API
+      run: |
+        cargo build -p harfrust_capi --features draw --target-dir target/capi-draw
+        cargo test -p harfrust_capi --features draw
+        cargo +1.85 check -p harfrust_capi --features draw,paint
+        cargo build -p harfrust_capi --features subset,paint
+        cargo test -p harfrust_capi --features subset,paint
+        python3 - <<'PY'
+        import ctypes, sys
+        suffix = "dylib" if sys.platform == "darwin" else "so"
+        for directory, draw, paint, subset in [
+            ("capi-default", False, False, False),
+            ("capi-draw", True, False, False),
+            (None, True, True, True),
+        ]:
+            base = f"target/{directory}/debug" if directory else "target/debug"
+            lib = ctypes.CDLL(f"{base}/libharfrust_c.{suffix}")
+            assert hasattr(lib, "hr_shape")
+            assert hasattr(lib, "hr_font_draw_glyph_or_fail") == draw
+            assert hasattr(lib, "hr_font_paint_glyph_or_fail") == paint
+            assert hasattr(lib, "hr_subset_or_fail") == subset
+        PY
+        cc -std=c99 -pedantic-errors -Wall -Wextra -Werror \
+          -Iharfrust_capi/include harfrust_capi/examples/rendering.c \
+          -Ltarget/debug -lharfrust_c -Wl,-rpath,"$PWD/target/debug" \
+          -o /tmp/hr-rendering
+        /tmp/hr-rendering harfrust_capi/tests/fonts/Rendering.ttf
+        c++ -x c++ -std=c++11 -pedantic-errors -Wall -Wextra -Werror \
+          -Iharfrust_capi/include harfrust_capi/examples/rendering.c \
+          -Ltarget/debug -lharfrust_c -Wl,-rpath,"$PWD/target/debug" \
+          -o /tmp/hr-rendering-cpp
+        /tmp/hr-rendering-cpp harfrust_capi/tests/fonts/Rendering.ttf
+
     - name: AAT C++ source compatibility
       run: |
         c++ -std=c++11 -pedantic-errors -Wall -Wextra -Werror \

harfrust_capi/Cargo.toml

@@ -14,10 +14,13 @@ categories.workspace = true
 [features]
 default = []
 subset = ["dep:skera", "dep:write-fonts"]
+draw = ["dep:skrifa"]
+paint = ["draw"]
 
 [dependencies]
 harfrust = { workspace = true, features = ["std"] }
 read-fonts.workspace = true
+skrifa = { version = "0.48.0", default-features = false, features = ["std"], optional = true }
 skera = { version = "0.8.0", optional = true }
 write-fonts = { version = "0.54.0", default-features = false, features = ["read"], optional = true }
 

harfrust_capi/README.md

@@ -80,6 +80,62 @@ cbindgen --config harfrust_capi/cbindgen.toml \
 
 Regenerate it after changing any `pub extern "C"` item.
 
+## Optional drawing and painting
+
+Enable `draw` for Skrifa-backed outline extraction, or `paint` for color glyph
+painting (`paint` also enables `draw`):
+
+```sh
+cargo build -p harfrust_capi --release --features draw,paint
+```
+
+These features are off by default. They use the same `hr_font_t`, `hr_face_t`
+and C library as shaping. Include `hr-draw.h` or `hr-paint.h` for native names,
+or `hr-hb-draw.h` / `hr-hb-paint.h` for HarfBuzz source compatibility. The paint
+header includes drawing. Subsetting can be enabled alongside either feature.
+
+`hr_font_draw_glyph_or_fail` extracts unhinted glyf, CFF, CFF2 and VARC outlines
+at the font's current normalized variation coordinates and independent X/Y
+scales. Draw callbacks receive HarfBuzz-style contour state, with quadratic
+to cubic fallback. Both the legacy custom font callbacks and callbacks that
+return success are supported, including inheritance from a parent font with
+different scales.
+
+`hr_font_paint_glyph_or_fail` traverses COLRv0/v1 paint graphs, including
+palettes, gradients, transforms, clips, composites and cached color glyph
+callbacks. SVG documents and CBDT/sbix PNG or BGRA images are delivered to the
+client's image callback. The client renders those formats and can retain an
+image with `hr_blob_reference`; gradient color lines are only valid during
+their callback. Missing `fill_glyph` and `push_group_for` callbacks use the
+HarfBuzz defaults. Malformed paint graphs return false and unwind open
+transforms, clips and groups.
+
+Rendering reads known tables directly and caches an assembled SFNT once per
+face. Callback faces work without table enumeration. This cache copies the
+rendering tables, so the feature has a per-face memory cost beyond shaping.
+
+Skrifa's outlines are geometrically compatible with HarfBuzz; redundant
+closing lines and CFF composite contour order can differ. VARC transform
+precision and bitmap extent rounding can also differ slightly. Hinting,
+bitmap masks, draw shape helpers, configurable draw/paint budgets, gradient
+preprocessing/tiling helpers and
+the deprecated `hb_font_get_glyph_shape` names are not exposed. Skrifa's own
+paint traversal limits remain in effect.
+
+Regenerate these headers and their aliases after changing the feature APIs:
+
+```sh
+cbindgen --config harfrust_capi/cbindgen-draw.toml \
+         harfrust_capi/src/draw.rs --output harfrust_capi/include/hr-draw.h
+cbindgen --config harfrust_capi/cbindgen-paint.toml \
+         harfrust_capi/src/paint.rs --output harfrust_capi/include/hr-paint.h
+python3 scripts/gen-hb-compat-header.py
+```
+
+[`examples/rendering.c`](examples/rendering.c) exercises both features as a
+C99 consumer. `tests/compare_draw_hb.py` and `tests/compare_paint_hb.py` take
+HarfRust and HarfBuzz shared library paths for differential checks.
+
 Packed colors use `hr_color_t` and `HR_COLOR(b, g, r, a)`, with channel
 accessors `hr_color_get_blue/green/red/alpha`. These common definitions are
 available without enabling painting.
@@ -145,7 +201,6 @@ same cache.
 
 The following HarfBuzz APIs are not exposed:
 
-- Drawing and painting callbacks (`hb_draw_funcs_t`, `hb_paint_funcs_t`).
 - Layout queries beyond the available GSUB/GPOS presence, lookup count, and
   glyph collection functions.
 - Custom Unicode callbacks (`hb_unicode_funcs_t`); HarfRust's own Unicode data

harfrust_capi/cbindgen-draw.toml

@@ -0,0 +1,15 @@
+language = "C"
+include_guard = "HARFRUST_DRAW_H"
+cpp_compat = true
+documentation = true
+style = "both"
+tab_width = 2
+includes = ["hr.h"]
+header = "/* Generated by cbindgen from harfrust_capi/src/draw.rs. */"
+
+trailer = """
+#define HR_DRAW_STATE_DEFAULT {0, 0.f, 0.f, 0.f, 0.f, {0}}
+"""
+
+[export]
+exclude = ["hr_bool_t", "hr_codepoint_t", "hr_destroy_func_t", "hr_user_data_key_t", "hr_font_t", "hr_font_funcs_t", "hr_blob_t", "hr_tag_t", "hr_glyph_extents_t"]

harfrust_capi/cbindgen-paint.toml

@@ -0,0 +1,12 @@
+language = "C"
+include_guard = "HARFRUST_PAINT_H"
+cpp_compat = true
+documentation = true
+style = "both"
+tab_width = 2
+includes = ["hr.h", "hr-draw.h"]
+after_includes = "struct hr_color_line_t;"
+header = "/* Generated by cbindgen from harfrust_capi/src/paint.rs. */"
+
+[export]
+exclude = ["hr_color_t", "hr_bool_t", "hr_codepoint_t", "hr_destroy_func_t", "hr_user_data_key_t", "hr_font_t", "hr_font_funcs_t", "hr_blob_t", "hr_tag_t", "hr_glyph_extents_t", "hr_draw_funcs_t"]

harfrust_capi/examples/rendering.c

@@ -0,0 +1,66 @@
+/* The same C99 consumer can be built against HarfRust or HarfBuzz. */
+#ifdef USE_HARFBUZZ
+#include <hb.h>
+#else
+#include <hr-hb-paint.h>
+#include <hr-hb-draw.h>
+#include <hr-hb-subset.h>
+#endif
+#include <assert.h>
+#include <stddef.h>
+
+typedef char draw_state_size[sizeof(hb_draw_state_t) == 48 ? 1 : -1];
+typedef char color_stop_size[sizeof(hb_color_stop_t) == 12 ? 1 : -1];
+typedef char color_line_size[sizeof(hb_color_line_t) == 13 * sizeof(void *) ? 1 : -1];
+
+static void line(hb_draw_funcs_t *funcs, void *data, hb_draw_state_t *state,
+                 float x, float y, void *user_data)
+{
+  (void)funcs; (void)x; (void)y; (void)user_data;
+  assert(state->path_open);
+  ++*(unsigned *)data;
+}
+
+static void color(hb_paint_funcs_t *funcs, void *data, hb_bool_t foreground,
+                  hb_color_t value, void *user_data)
+{
+  (void)funcs; (void)foreground; (void)user_data;
+  assert(hb_color_get_alpha(value) == 255);
+  ++*(unsigned *)data;
+}
+
+int main(int argc, char **argv)
+{
+  hb_blob_t *blob;
+  hb_face_t *face;
+  hb_font_t *font;
+  hb_draw_funcs_t *draw;
+  hb_paint_funcs_t *paint;
+  hb_draw_state_t state = HB_DRAW_STATE_DEFAULT;
+  unsigned lines = 0, colors = 0;
+  assert(argc == 2);
+  blob = hb_blob_create_from_file(argv[1]);
+  face = hb_face_create(blob, 0);
+  font = hb_font_create(face);
+  draw = hb_draw_funcs_create();
+  paint = hb_paint_funcs_create();
+  hb_draw_funcs_set_line_to_func(draw, line, NULL, NULL);
+  hb_paint_funcs_set_color_func(paint, color, NULL, NULL);
+  hb_draw_funcs_make_immutable(draw);
+  hb_paint_funcs_make_immutable(paint);
+  assert(hb_font_draw_glyph_or_fail(font, 1, draw, &lines));
+  assert(lines == 3);
+  assert(hb_font_paint_glyph_or_fail(font, 2, paint, &colors, 0,
+                                   HB_COLOR(0xaa, 0xbb, 0xcc, 0xff)));
+  assert(colors == 2);
+  hb_draw_move_to(draw, &lines, &state, 0, 0);
+  hb_draw_line_to(draw, &lines, &state, 1, 1);
+  hb_draw_close_path(draw, &lines, &state);
+  assert(!state.path_open && lines == 5);
+  hb_paint_funcs_destroy(paint);
+  hb_draw_funcs_destroy(draw);
+  hb_font_destroy(font);
+  hb_face_destroy(face);
+  hb_blob_destroy(blob);
+  return 0;
+}