[paint] Add HB_PAINT_IMAGE_FORMAT_BGRA and use it in hb-ft

Now hb-ft can render color emoji as well.

Just left COLRv2.

docs/harfbuzz-sections.txt

@@ -244,6 +244,7 @@ hb_paint_color_func_t
 hb_paint_funcs_set_color_func
 HB_PAINT_IMAGE_FORMAT_PNG
 HB_PAINT_IMAGE_FORMAT_SVG
+HB_PAINT_IMAGE_FORMAT_BGRA
 hb_paint_image_func_t
 hb_paint_funcs_set_image_func
 hb_color_line_t
@@ -373,6 +374,7 @@ hb_font_get_glyph_v_origin
 hb_font_get_glyph_origin_for_direction
 hb_font_get_glyph_name
 hb_font_get_glyph_shape
+hb_font_draw_glyph
 hb_font_paint_glyph
 hb_font_get_nominal_glyph
 hb_font_get_nominal_glyphs
@@ -436,6 +438,8 @@ hb_font_get_glyph_name_func_t
 hb_font_funcs_set_glyph_name_func
 hb_font_get_glyph_shape_func_t
 hb_font_funcs_set_glyph_shape_func
+hb_font_draw_glyph_func_t
+hb_font_funcs_set_draw_glyph_func
 hb_font_paint_glyph_func_t
 hb_font_funcs_set_paint_glyph_func
 hb_font_get_nominal_glyph_func_t

src/hb-ft.cc

@@ -830,7 +830,8 @@ hb_ft_paint_glyph (hb_font_t *font,
   /* We release the lock before calling into callbacks, such that
    * eg. draw API can call back into the face.*/
 
-  if (unlikely (FT_Load_Glyph (ft_face, gid, ft_font->load_flags)))
+  if (unlikely (FT_Load_Glyph (ft_face, gid,
+			       ft_font->load_flags | FT_LOAD_COLOR)))
     return;
 
   if (ft_face->glyph->format == FT_GLYPH_FORMAT_OUTLINE)
@@ -898,6 +899,42 @@ hb_ft_paint_glyph (hb_font_t *font,
     return;
   }
 
+  auto *glyph = ft_face->glyph;
+  if (glyph->format == FT_GLYPH_FORMAT_BITMAP)
+  {
+    auto &bitmap = glyph->bitmap;
+    if (bitmap.pixel_mode == FT_PIXEL_MODE_BGRA)
+    {
+      if (bitmap.pitch != (signed) bitmap.width * 4)
+        return;
+
+      ft_font->lock.unlock ();
+
+      hb_blob_t *blob = hb_blob_create ((const char *) bitmap.buffer,
+					bitmap.pitch * bitmap.rows,
+					HB_MEMORY_MODE_DUPLICATE,
+					nullptr, nullptr);
+
+      hb_glyph_extents_t extents;
+      if (!hb_font_get_glyph_extents (font, gid, &extents))
+	goto out;
+
+      paint_funcs->image (paint_data,
+			  blob,
+			  bitmap.width,
+			  bitmap.rows,
+			  HB_PAINT_IMAGE_FORMAT_BGRA,
+			  font->slant_xy,
+			  &extents);
+
+    out:
+      hb_blob_destroy (blob);
+      ft_font->lock.lock ();
+    }
+
+    return;
+  }
+
   /* TODO Support image, COLRv0/1. */
 }
 #endif

src/hb-paint.h

@@ -227,17 +227,31 @@ typedef void (*hb_paint_color_func_t) (hb_paint_funcs_t *funcs,
 /**
  * HB_PAINT_IMAGE_FORMAT_PNG:
  *
- * Tag identifying png images in #hb_paint_image_func_t callbacks.
+ * Tag identifying PNG images in #hb_paint_image_func_t callbacks.
+ *
+ * Since: REPLACEME
  */
 #define HB_PAINT_IMAGE_FORMAT_PNG HB_TAG('p','n','g',' ')
 
 /**
  * HB_PAINT_IMAGE_FORMAT_SVG:
  *
- * Tag identifying svg images in #hb_paint_image_func_t callbacks.
+ * Tag identifying SVG images in #hb_paint_image_func_t callbacks.
+ *
+ * Since: REPLACEME
  */
 #define HB_PAINT_IMAGE_FORMAT_SVG HB_TAG('s','v','g',' ')
 
+/**
+ * HB_PAINT_IMAGE_FORMAT_BGRA:
+ *
+ * Tag identifying raw pixel-data images in #hb_paint_image_func_t callbacks.
+ * The data is in BGRA pre-multiplied sRGBA color-space format.
+ *
+ * Since: REPLACEME
+ */
+#define HB_PAINT_IMAGE_FORMAT_BGRA HB_TAG('B','G','R','A')
+
 /**
  * hb_paint_image_func_t:
  * @funcs: paint functions object

util/hb-cairo-utils.c

@@ -98,6 +98,14 @@ read_blob (void *closure,
 }
 #endif
 
+static const cairo_user_data_key_t *_hb_cairo_surface_blob_user_data_key = {0};
+
+static void
+_hb_cairo_destroy_blob (void *p)
+{
+  hb_blob_destroy ((hb_blob_t *) p);
+}
+
 void
 hb_cairo_paint_glyph_image (cairo_t *cr,
                             hb_blob_t *blob,
@@ -107,19 +115,68 @@ hb_cairo_paint_glyph_image (cairo_t *cr,
                             float slant,
                             hb_glyph_extents_t *extents)
 {
-#ifdef CAIRO_HAS_PNG_FUNCTIONS
-  if (format != HB_PAINT_IMAGE_FORMAT_PNG || !extents)
+  if (!extents) /* SVG currently. */
     return;
 
+  cairo_surface_t *surface = NULL;
+
+#ifdef CAIRO_HAS_PNG_FUNCTIONS
+  if (format == HB_PAINT_IMAGE_FORMAT_PNG)
+  {
     read_blob_data_t r;
     r.blob = blob;
     r.offset = 0;
-  cairo_surface_t *surface = cairo_image_surface_create_from_png_stream (read_blob, &r);
+    surface = cairo_image_surface_create_from_png_stream (read_blob, &r);
 
     /* For PNG, width,height can be unreliable, as is the case for NotoColorEmoji :(.
      * Just pull them out of the surface. */
     width = cairo_image_surface_get_width (surface);
     height = cairo_image_surface_get_width (surface);
+  }
+  else
+#endif
+  if (format == HB_PAINT_IMAGE_FORMAT_BGRA)
+  {
+    /* Byte-endian conversion. */
+    unsigned data_size = hb_blob_get_length (blob);
+    if (data_size < width * height * 4)
+      return;
+
+    unsigned char *data;
+    if (__BYTE_ORDER == __BIG_ENDIAN)
+    {
+      data = (unsigned char *) hb_blob_get_data_writable (blob, NULL);
+      if (!data)
+        return;
+
+      unsigned count = width * height * 4;
+      for (unsigned i = 0; i < count; i += 4)
+      {
+        unsigned char b;
+	b = data[i];
+	data[i] = data[i+3];
+	data[i+3] = b;
+	b = data[i+1];
+	data[i+1] = data[i+2];
+	data[i+2] = b;
+      }
+    }
+    else
+      data = (unsigned char *) hb_blob_get_data (blob, NULL);
+
+    surface = cairo_image_surface_create_for_data (data,
+						   CAIRO_FORMAT_ARGB32,
+						   width, height,
+						   width * 4);
+
+    cairo_surface_set_user_data (surface,
+				 _hb_cairo_surface_blob_user_data_key,
+				 hb_blob_reference (blob),
+				 _hb_cairo_destroy_blob);
+  }
+
+  if (!surface)
+    return;
 
   cairo_pattern_t *pattern = cairo_pattern_create_for_surface (surface);
   cairo_pattern_set_extend (pattern, CAIRO_EXTEND_PAD);
@@ -141,7 +198,6 @@ hb_cairo_paint_glyph_image (cairo_t *cr,
 
   cairo_pattern_destroy (pattern);
   cairo_surface_destroy (surface);
-#endif
 }
 
 static void