[paint] Add slant to image() callback

And slant images in hb-view.

src/hb-ot-color-cbdt-table.hh

@@ -948,7 +948,7 @@ struct CBDT
       if (unlikely (!hb_font_get_glyph_extents (font, glyph, &extents)))
         return false;
 
-      funcs->image (data, blob, HB_PAINT_IMAGE_FORMAT_PNG, &extents);
+      funcs->image (data, blob, HB_PAINT_IMAGE_FORMAT_PNG, font->slant_xy, &extents);
 
       hb_blob_destroy (blob);
       return true;

src/hb-ot-color-sbix-table.hh

@@ -248,7 +248,7 @@ struct sbix
       if (!hb_font_get_glyph_extents (font, glyph, &extents))
         return false;
 
-      funcs->image (data, blob, HB_PAINT_IMAGE_FORMAT_PNG, &extents);
+      funcs->image (data, blob, HB_PAINT_IMAGE_FORMAT_PNG, font->slant_xy, &extents);
 
       hb_blob_destroy (blob);
       return true;

src/hb-ot-color-svg-table.hh

@@ -103,7 +103,7 @@ struct SVG
       if (blob == hb_blob_get_empty ())
         return false;
 
-      funcs->image (data, blob, HB_PAINT_IMAGE_FORMAT_SVG, nullptr);
+      funcs->image (data, blob, HB_PAINT_IMAGE_FORMAT_SVG, font->slant_xy, nullptr);
 
       hb_blob_destroy (blob);
       return true;

src/hb-paint.cc

@@ -78,6 +78,7 @@ static void
 hb_paint_image_nil (hb_paint_funcs_t *funcs, void *paint_data,
                     hb_blob_t *image,
                     hb_tag_t format,
+                    float slant_xy,
                     hb_glyph_extents_t *extents,
                     void *user_data) {}
 

src/hb-paint.h

@@ -264,6 +264,7 @@ typedef void (*hb_paint_image_func_t) (hb_paint_funcs_t *funcs,
                                        void *paint_data,
                                        hb_blob_t *image,
                                        hb_tag_t format,
+                                       float slant,
                                        hb_glyph_extents_t *extents,
                                        void *user_data);
 

src/hb-paint.hh

@@ -100,9 +100,10 @@ struct hb_paint_funcs_t
   void image (void *paint_data,
               hb_blob_t *image,
               hb_tag_t format,
+              float slant,
               hb_glyph_extents_t *extents)
   { func.image (this, paint_data,
-                image, format, extents,
+                image, format, slant, extents,
                 !user_data ? nullptr : user_data->image); }
   void linear_gradient (void *paint_data,
                         hb_color_line_t *color_line,

util/hb-cairo-utils.c

@@ -100,6 +100,7 @@ void
 hb_cairo_paint_glyph_image (cairo_t *cr,
                             hb_blob_t *blob,
                             hb_tag_t format,
+                            float slant,
                             hb_glyph_extents_t *extents)
 {
 #ifdef CAIRO_HAS_PNG_FUNCTIONS
@@ -119,6 +120,12 @@ hb_cairo_paint_glyph_image (cairo_t *cr,
   cairo_matrix_t matrix = {(double) width, 0, 0, (double) height, 0, 0};
   cairo_pattern_set_matrix (pattern, &matrix);
 
+  /* Undo slant in the extents and apply it in the context. */
+  extents->width -= extents->height * slant;
+  extents->x_bearing -= extents->y_bearing * slant;
+  cairo_matrix_t cairo_matrix = {1., 0., slant, 1., 0., 0.};
+  cairo_transform (cr, &cairo_matrix);
+
   cairo_translate (cr, extents->x_bearing, extents->y_bearing);
   cairo_scale (cr, extents->width, extents->height);
   cairo_set_source (cr, pattern);

util/hb-cairo-utils.h

@@ -73,6 +73,7 @@ hb_paint_composite_mode_to_cairo (hb_paint_composite_mode_t mode)
 void hb_cairo_paint_glyph_image (cairo_t *cr,
                                  hb_blob_t *blob,
                                  hb_tag_t format,
+                                 float slant,
                                  hb_glyph_extents_t *extents);
 
 void hb_cairo_paint_linear_gradient (cairo_t *cr,

util/helper-cairo-user.hh

@@ -222,12 +222,13 @@ paint_image (hb_paint_funcs_t *funcs,
              void *paint_data,
              hb_blob_t *blob,
              hb_tag_t format,
+             float slant,
              hb_glyph_extents_t *extents,
              void *user_data)
 {
   cairo_t *cr = (cairo_t *)paint_data;
 
-  hb_cairo_paint_glyph_image (cr, blob, format, extents);
+  hb_cairo_paint_glyph_image (cr, blob, format, slant, extents);
 }
 
 static void