Set text in a stack of fonts: each grapheme cluster in the first that has it

vega_layout takes fonts in order of preference (VegaFonts). A grapheme
cluster goes to the first font that has all its characters (default
ignorables aside: shaping hides them); a cluster of Common and Inherited
characters stays in the font before it when that one has it, so the spaces
between Arabic words stay in the Arabic font; failing that, the first font
with its first character, else the first font. Runs split where the font
changes too. Positions are in the first font's units, a run's pen scaled
as a whole so rounding does not add up. Callers can narrow what a font
has (a symbol file holds only the glyphs its codes reach).

vega_default_ignorable is shape.c's HarfBuzz 10.2 set, now public.

1 files changed, 28 insertions, 9 deletions

diff --git a/text/layout.h b/text/layout.h
index 9282536..f5aeb89 100644
--- a/text/layout.h
+++ b/text/layout.h
@@ -3,14 +3,16 @@
 #include "shape.h"
 
 /* A paragraph set into lines (docs/design/004-text.md): its bidi levels
- * (UAX #9), lines broken where UAX #14 allows and they fit (spaces at a
- * line's end hang past it), and each line's runs (one level, one script)
- * shaped and put in visual order. Positions are in the font's units: x
- * from the paragraph's left edge, y up from the line's baseline. */
+ * (UAX #9), a font for each grapheme cluster, lines broken where UAX #14
+ * allows and they fit (spaces at a line's end hang past it), and each
+ * line's runs (one level, one script, one font) shaped and put in visual
+ * order. Positions are in the first font's units: x from the paragraph's
+ * left edge, y up from the line's baseline. */
 typedef struct {
-    uint32_t glyph;   /* the font's: its symbol is VEGA_GLYPH_SYMBOLS + glyph */
+    uint32_t glyph;   /* its font's: its symbol is VEGA_GLYPH_SYMBOLS + glyph */
     uint32_t cluster; /* the paragraph index of the first character it came from */
     int32_t x, y, advance;
+    uint32_t font;    /* which of the fonts */
 } VegaPlaced;
 typedef struct {
     size_t first, count; /* its glyphs, left to right */
@@ -29,10 +31,27 @@ typedef struct {
     size_t work_size, lines_allocated, glyphs_allocated;
 } VegaLayout;
 
-/* Set count characters in lines of at most width (0: no limit) with the
- * font's shaping; direction is VEGA_BIDI_AUTO, _LTR or _RTL. The layout
- * holds the result until it is set again; false without memory. */
-bool vega_layout(VegaLayout *, VegaShaper *, const VegaShaping *, const uint32_t *codes, size_t count, int direction,
+/* What text is set in: fonts in order of preference, each cluster in the
+ * first that has all its characters (default ignorables aside: shaping
+ * hides them), a cluster of Common and Inherited characters (spaces,
+ * digits, punctuation) in the font before it when that one has them; no
+ * font having them all, the first that has its first character, else the
+ * first font. has says whether a font has a character, NULL whether its
+ * character map does: a font whose glyphs are not all at hand can say it
+ * lacks the others. */
+enum { VEGA_LAYOUT_FONTS = 16 };
+typedef struct {
+    const VegaShaping *fonts[VEGA_LAYOUT_FONTS];
+    unsigned count;
+    bool (*has)(void *context, unsigned font, uint32_t code);
+    void *context;
+} VegaFonts;
+
+/* Set count characters in lines of at most width (0: no limit) in the
+ * fonts; direction is VEGA_BIDI_AUTO, _LTR or _RTL. The layout holds the
+ * result until it is set again; false without memory, or when a run's font
+ * has no plan for its script (nor for Common). */
+bool vega_layout(VegaLayout *, VegaShaper *, const VegaFonts *, const uint32_t *codes, size_t count, int direction,
                  int32_t width);
 void vega_layout_free(VegaLayout *);
 #endif