Add glyph-level text rendering to Cairo bindings

Message

Add cairo-show-glyphs for rendering positioned glyphs from HarfBuzz shaping output. Add cairo-ft-font-face-create for creating Cairo font faces from FreeType faces, cairo-set-font-face, cairo-font-face-destroy, and cairo-glyph-layout struct. Enables the full FreeType + HarfBuzz + Cairo text rendering pipeline.

Changed

 src/cairo.sgl | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

Diff

src/cairo.sglmodified

@@ -173,6 +173,13 @@

173

cairo-text-extents

174

cairo-font-extents

175

+176

;; Glyph rendering

+177

cairo-glyph-layout

+178

cairo-show-glyphs

+179

cairo-ft-font-face-create

+180

cairo-set-font-face

+181

cairo-font-face-destroy

+182

183

;; Transforms

184

cairo-translate

185

cairo-scale

@@ -317,6 +324,13 @@

324

x0: ffi/double

325

y0: ffi/double))

326

+327

;; cairo_glyph_t — for glyph-level text rendering

+328

(define cairo-glyph-layout

+329

(c-struct-layout

+330

index: ffi/ulong

+331

x: ffi/double

+332

y: ffi/double))

+333

334

;; ============================================================

335

;; Finalizer Pointers (looked up once)

336

;; ============================================================

@@ -324,6 +338,7 @@

338

(define %cairo-destroy-ptr (c-symbol cairo-lib "cairo_destroy"))

339

(define %surface-destroy-ptr (c-symbol cairo-lib "cairo_surface_destroy"))

340

(define %pattern-destroy-ptr (c-symbol cairo-lib "cairo_pattern_destroy"))

+341

(define %font-face-destroy-ptr (c-symbol cairo-lib "cairo_font_face_destroy"))

342

343

;; ============================================================

344

;; Raw Function Bindings

@@ -600,6 +615,23 @@

615

(c-function cairo-lib "cairo_font_extents"

616

(list ffi/pointer ffi/pointer) ffi/void))

617

+618

;; Glyph rendering

+619

(define %show-glyphs

+620

(c-function cairo-lib "cairo_show_glyphs"

+621

(list ffi/pointer ffi/pointer ffi/int) ffi/void))

+622

+623

(define %set-font-face

+624

(c-function cairo-lib "cairo_set_font_face"

+625

(list ffi/pointer ffi/pointer) ffi/void))

+626

+627

(define %font-face-destroy

+628

(c-function cairo-lib "cairo_font_face_destroy"

+629

(list ffi/pointer) ffi/void))

+630

+631

(define %ft-font-face-create

+632

(c-function cairo-lib "cairo_ft_font_face_create_for_ft_face"

+633

(list ffi/pointer ffi/int) ffi/pointer))

+634

635

;; Transforms

636

(define %translate

637

(c-function cairo-lib "cairo_translate"

@@ -1035,6 +1067,50 @@

1067

(%font-extents cr extents)

1068

(c-struct->dict extents cairo-font-extents-layout))))

1069

+1070

;; ============================================================

+1071

;; Public API — Glyph Rendering

+1072

;; ============================================================

+1073

+1074

;;; Render glyphs at specified positions on a Cairo context.

+1075

;;;

+1076

;;; GLYPHS is a list of dicts with keys: index: (glyph index),

+1077

;;; x: (x position), y: (y position).

+1078

(define (cairo-show-glyphs cr glyphs)

+1079

(: pointer? list? -> void?)

+1080

(let* ((n (length glyphs))

+1081

(glyph-size (c-struct-size cairo-glyph-layout))

+1082

(buf (c-alloc (* n glyph-size))))

+1083

(let loop ((i 0) (gs glyphs))

+1084

(when (pair? gs)

+1085

(let ((g (car gs))

+1086

(ptr (pointer+ buf (* i glyph-size))))

+1087

(c-struct-set! ptr cairo-glyph-layout index: (dict-ref g index:))

+1088

(c-struct-set! ptr cairo-glyph-layout x: (dict-ref g x:))

+1089

(c-struct-set! ptr cairo-glyph-layout y: (dict-ref g y:))

+1090

(loop (+ i 1) (cdr gs)))))

+1091

(%show-glyphs cr buf n)

+1092

(c-free buf)))

+1093

+1094

;;; Create a Cairo font face from a FreeType face.

+1095

;;;

+1096

;;; Requires Cairo to be built with FreeType support.

+1097

(define (cairo-ft-font-face-create ft-face load-flags)

+1098

(: pointer? integer? -> pointer?)

+1099

(let ((face (%ft-font-face-create ft-face load-flags)))

+1100

(set-pointer-finalizer! face %font-face-destroy-ptr)

+1101

face))

+1102

+1103

;;; Set the font face for a Cairo context.

+1104

(define (cairo-set-font-face cr face)

+1105

(: pointer? pointer? -> void?)

+1106

(%set-font-face cr face))

+1107

+1108

;;; Destroy a Cairo font face.

+1109

(define (cairo-font-face-destroy face)

+1110

(: pointer? -> void?)

+1111

(set-pointer-finalizer! face #f)

+1112

(%font-face-destroy face))

+1113

1114

;; ============================================================

1115

;; Public API — Transforms

1116

;; ============================================================