Robert Allan JamesandClaude Sonnet 5
70b6918279
ttf_glyph_outline() decodes simple-glyph flag/coordinate runs and recursively resolves composite components into a caller-supplied point/ contour-end buffer, in Q48.16. Composite scale/rotation/skew transforms are rejected with TTF_ERR_UNSUPPORTED rather than mis-rendered, since the shared q48_mul/q48_div are unsigned-only; translation-only composites (the only kind the v1 glyph repertoire uses) apply cleanly via q48_add. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
189 lines
6.8 KiB
C
189 lines
6.8 KiB
C
/*
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StarForth — Steady-State Virtual Machine Runtime
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Copyright (c) 2023–2025 Robert A. James
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All rights reserved.
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This file is part of the StarForth project.
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Licensed under the StarForth License, Version 1.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at:
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https://github.com/star.4th@proton.me/StarForth/LICENSE.txt
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This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
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express or implied, including but not limited to the warranties of
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merchantability, fitness for a particular purpose, and noninfringement.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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/**
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* ttf.h - TrueType font parser core (Freestanding)
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*
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* FABRIC.md item 4.3.7. Reads a TTF's sfnt directory plus head/maxp/loca/
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* glyf/cmap tables, resolving a Unicode codepoint to a glyph index and its
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* outline header (contour count, bounding box). Does NOT extract outline
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* points or rasterize — that is 4.3.7a/4.3.7c. No floating point; all
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* fields read here are raw integers straight from the font's own
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* big-endian on-disk format (see FABRIC.md §27.7 decision #2 for why the
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* Q48.16-vs-float call was made, and why it doesn't bind this file, which
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* never scales anything).
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*
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* cmap: only format 4 (Windows/Unicode BMP) subtables are resolved. This
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* covers ASCII and all of the BMP, which is what the v1 glyph repertoire
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* (§27.6.4) needs. Format 12 (supplementary planes) is deferred — no
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* v1 glyph requires it.
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*/
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#ifndef STARKERNEL_TTF_H
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#define STARKERNEL_TTF_H
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#include <stdint.h>
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#include <stddef.h>
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#include "q48_16.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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#define TTF_OK 0
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#define TTF_ERR_BAD_SFNT -1
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#define TTF_ERR_TABLE_MISSING -2
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#define TTF_ERR_BAD_TABLE -3
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#define TTF_ERR_BAD_GLYPH_INDEX -4
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#define TTF_ERR_OUT_OF_BOUNDS -5
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#define TTF_ERR_TOO_MANY_POINTS -6
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#define TTF_ERR_TOO_MANY_CONTOURS -7
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#define TTF_ERR_TOO_DEEP -8 /* composite glyph nesting exceeded TTF_MAX_COMPOSITE_DEPTH */
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#define TTF_ERR_UNSUPPORTED -9 /* e.g. a non-identity composite transform or point-matched
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* component args — see ttf.c's file header comment; not a
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* malformed font, just a code path this parser doesn't
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* implement yet */
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/* Recursion guard for nested composite glyphs (a component referencing a
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* component). The TTF spec doesn't hard-cap this; this is a defensive
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* limit for freestanding/kernel-stack safety. */
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#define TTF_MAX_COMPOSITE_DEPTH 8
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/** Glyph index returned for "no mapping" by ttf_codepoint_to_glyph(). */
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#define TTF_GLYPH_MISSING 0
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/**
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* Parsed font handle. Borrows the caller's buffer (does not copy or own
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* it) — the buffer must outlive the ttf_font_t.
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*/
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typedef struct {
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const uint8_t *data;
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uint32_t size;
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uint32_t head_off;
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uint32_t maxp_off;
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uint32_t loca_off;
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uint32_t loca_len;
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uint32_t glyf_off;
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uint32_t glyf_len;
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uint16_t units_per_em;
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int16_t index_to_loc_format; /* 0 = Offset16 (x2), 1 = Offset32 */
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uint16_t num_glyphs;
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/* Selected cmap subtable (format 4 only, see file header comment). */
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uint32_t cmap_subtable_off;
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int has_cmap;
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} ttf_font_t;
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/** Raw glyf record header, per §27.6/4.3.7's "done when" clause. */
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typedef struct {
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int16_t num_contours; /* >= 0 simple glyph, < 0 composite glyph */
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int16_t x_min;
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int16_t y_min;
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int16_t x_max;
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int16_t y_max;
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uint32_t glyf_offset; /* absolute file offset of this glyph's record */
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uint32_t glyf_length; /* bytes; 0 for an empty glyph (e.g. space) */
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} ttf_glyph_header_t;
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/**
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* ttf_parse - Locate and validate the sfnt directory and the head/maxp/
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* loca/glyf tables (cmap is optional; ttf_codepoint_to_glyph() fails
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* cleanly if absent). Does not copy `data` — `out` borrows it.
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*
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* @param data Whole .ttf file contents
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* @param size Length of data in bytes
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* @param out Parsed handle to populate
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* @return TTF_OK, or a TTF_ERR_* code
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*/
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int ttf_parse(const uint8_t *data, uint32_t size, ttf_font_t *out);
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/**
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* ttf_codepoint_to_glyph - Resolve a Unicode codepoint via the font's
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* format-4 cmap subtable.
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*
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* @return glyph index, or TTF_GLYPH_MISSING if unmapped or no cmap
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*/
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uint32_t ttf_codepoint_to_glyph(const ttf_font_t *font, uint32_t codepoint);
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/**
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* ttf_glyph_header - Read a glyph's outline header (contour count,
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* bounding box) via loca + glyf. Does not extract contour points.
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*
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* @param glyph_index As returned by ttf_codepoint_to_glyph()
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* @param out Header to populate
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* @return TTF_OK, or a TTF_ERR_* code
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*/
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int ttf_glyph_header(const ttf_font_t *font, uint32_t glyph_index,
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ttf_glyph_header_t *out);
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/** One outline point, in raw font design units (NOT scaled by unitsPerEm —
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* that's the caller's job, same convention as ttf_glyph_header_t's bbox),
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* expressed in Q48.16. Two's-complement negative values are expected and
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* correct for q48_add/q48_sub and for q48_from_u64-style left-shift
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* conversion; this module never calls q48_mul/q48_div on outline
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* coordinates (see ttf.c's file header comment for why). */
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typedef struct {
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q48_16_t x, y;
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uint8_t on_curve;
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} ttf_point_t;
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/** Simple- and composite-glyph outline, flattened to one point list plus
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* per-contour end indices (TrueType convention: contour_ends[c] is the
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* index of the LAST point of contour c, inclusive; points are shared
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* across contours only in the sense that contour c+1 starts right after
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* contour_ends[c]). Caller supplies both backing arrays — this module
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* never allocates. */
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typedef struct {
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ttf_point_t *points;
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uint32_t max_points;
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uint32_t point_count;
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uint16_t *contour_ends;
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uint32_t max_contours;
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uint32_t contour_count;
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} ttf_outline_t;
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/**
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* ttf_glyph_outline - Extract a glyph's outline (simple or composite,
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* recursively resolving composite components) into caller-supplied
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* buffers.
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*
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* Composite components with a non-identity transform (any scale/rotation/
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* skew, i.e. anything but a pure (dx,dy) translation) or with
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* point-matched (rather than xy-offset) placement args return
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* TTF_ERR_UNSUPPORTED rather than silently producing a wrong outline —
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* see ttf.c's file header comment for why, and check that limitation
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* before relying on this for an arbitrary font.
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*
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* @return TTF_OK, or a TTF_ERR_* code (including TTF_ERR_TOO_MANY_POINTS/
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* _CONTOURS if a caller buffer is too small, and TTF_ERR_TOO_DEEP
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* if composite nesting exceeds TTF_MAX_COMPOSITE_DEPTH)
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*/
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int ttf_glyph_outline(const ttf_font_t *font, uint32_t glyph_index, ttf_outline_t *out);
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#ifdef __cplusplus
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}
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#endif
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#endif /* STARKERNEL_TTF_H */ |