[paint] Set up root transform in one place

Instead of spreading this in all the tables,
make hb_paint_funcs_t provide a push/pop_root_transform
that does all the setup.

src/OT/glyf/glyf.hh

@@ -335,21 +335,13 @@ struct glyf_accelerator_t
 
   bool paint_glyph (hb_font_t *font, hb_codepoint_t gid, hb_paint_funcs_t *funcs, void *data) const
   {
-    int xscale, yscale;
+    funcs->push_root_transform (data, font);
-    unsigned int upem;
-
-    hb_font_get_scale (font, &xscale, &yscale);
-    upem = hb_face_get_upem (hb_font_get_face (font));
-
-    funcs->push_transform (data, xscale/(float)upem, 0,
-                                 0, yscale/(float)upem,
-                                 0, 0);
 
     funcs->push_clip_glyph (data, gid);
     funcs->color (data, 0xffff, 1.);
     funcs->pop_clip (data);
 
-    funcs->pop_transform (data);
+    funcs->pop_root_transform (data);
 
     return false;
   }

src/hb-ot-cff1-table.cc

@@ -555,21 +555,13 @@ bool _get_path (const OT::cff1::accelerator_t *cff, hb_font_t *font, hb_codepoin
 
 bool OT::cff1::accelerator_t::paint_glyph (hb_font_t *font, hb_codepoint_t glyph, hb_paint_funcs_t *funcs, void *data) const
 {
-    int xscale, yscale;
+    funcs->push_root_transform (data, font);
-    unsigned int upem;
-
-    hb_font_get_scale (font, &xscale, &yscale);
-    upem = hb_face_get_upem (hb_font_get_face (font));
-
-    funcs->push_transform (data, xscale/(float)upem, 0,
-                                 0, yscale/(float)upem,
-                                 0, 0);
 
     funcs->push_clip_glyph (data, glyph);
     funcs->color (data, 0xffff, 1.);
     funcs->pop_clip (data);
 
-    funcs->pop_transform (data);
+    funcs->pop_root_transform (data);
 
     return false;
 }

src/hb-ot-cff2-table.cc

@@ -145,21 +145,13 @@ bool OT::cff2::accelerator_t::get_extents (hb_font_t *font,
 
 bool OT::cff2::accelerator_t::paint_glyph (hb_font_t *font, hb_codepoint_t glyph, hb_paint_funcs_t *funcs, void *data) const
 {
-    int xscale, yscale;
+    funcs->push_root_transform (data, font);
-    unsigned int upem;
-
-    hb_font_get_scale (font, &xscale, &yscale);
-    upem = hb_face_get_upem (hb_font_get_face (font));
-
-    funcs->push_transform (data, xscale/(float)upem, 0,
-                                 0, yscale/(float)upem,
-                                 0, 0);
 
     funcs->push_clip_glyph (data, glyph);
     funcs->color (data, 0xffff, 1.);
     funcs->pop_clip (data);
 
-    funcs->pop_transform (data);
+    funcs->pop_root_transform (data);
 
     return false;
 }

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

@@ -1929,24 +1929,15 @@ struct COLR
 
     hb_paint_context_t c (this, funcs, data, instancer);
 
-    int xscale, yscale;
-    unsigned int upem;
-
-    hb_font_get_scale (font, &xscale, &yscale);
-    upem = hb_face_get_upem (hb_font_get_face (font));
-
     const Paint *paint = get_base_glyph_paint (glyph);
     if (paint)
     {
       // COLRv1 glyph
-      // FIXME handle slant
+      c.funcs->push_root_transform (data, font);
-      funcs->push_transform (data, xscale/(float)upem, 0,
-                                   0, yscale/(float)upem,
-                                   0, 0);
 
       c.recurse (*paint);
 
-      c.funcs->pop_transform (c.data);
+      c.funcs->pop_root_transform (c.data);
 
       return true;
     }
@@ -1955,10 +1946,7 @@ struct COLR
     if (record && ((hb_codepoint_t) record->glyphId == glyph))
     {
       // COLRv0 glyph
-      // FIXME handle slant
+      funcs->push_root_transform (data, font);
-      funcs->push_transform (data, xscale/(float)upem, 0,
-                                   0, yscale/(float)upem,
-                                   0, 0);
 
       for (const auto &r : (this+layersZ).as_array (numLayers)
 			   .sub_array (record->firstLayerIdx, record->numLayers))
@@ -1968,7 +1956,7 @@ struct COLR
         c.funcs->pop_clip (c.data);
       }
 
-      c.funcs->pop_transform (c.data);
+      c.funcs->pop_root_transform (c.data);
 
       return true;
     }

src/hb-paint.hh

@@ -132,6 +132,18 @@ struct hb_paint_funcs_t
                     mode,
                     !user_data ? nullptr : user_data->pop_group); }
 
+  void push_root_transform (void *paint_data,
+                            hb_font_t *font)
+  {
+    int xscale, yscale;
+    float upem;
+    hb_font_get_scale (font, &xscale, &yscale);
+    upem = hb_face_get_upem (hb_font_get_face (font));
+    func.push_transform (this, paint_data, xscale/upem, 0, 0, yscale/upem, 0, 0,
+                         !user_data ? nullptr : user_data->push_transform); }
+  void pop_root_transform (void *paint_data)
+  { func.pop_transform (this, paint_data,
+                        !user_data ? nullptr : user_data->pop_transform); }
 };
 DECLARE_NULL_INSTANCE (hb_paint_funcs_t);