[paint] Add internal push_skew/pop_skew API

src/hb-ft-colr.hh

@@ -374,14 +374,14 @@ _hb_ft_paint (hb_ft_paint_context_t *c,
     {
       float dx = paint.u.skew.center_x / 65536.f;
       float dy = paint.u.skew.center_y / 65536.f;
-      float x = +tanf (paint.u.skew.x_skew_angle / 65536.f * (float) M_PI);
-      float y = -tanf (paint.u.skew.y_skew_angle / 65536.f * (float) M_PI);
+      float sx = paint.u.skew.x_skew_angle / 65536.f;
+      float sy = paint.u.skew.y_skew_angle / 65536.f;
       c->funcs->push_translate (c->data, +dx, +dy);
-      c->funcs->push_transform (c->data, 1., y, x, 1., 0., 0.);
+      c->funcs->push_skew (c->data, sx, sy);
       c->funcs->push_translate (c->data, -dx, -dy);
       c->recurse (paint.u.skew.paint);
       c->funcs->pop_translate (c->data, -dx, -dy);
-      c->funcs->pop_transform (c->data);
+      c->funcs->pop_skew (c->data, sx, sy);
       c->funcs->pop_translate (c->data, +dx, +dy);
     }
     break;

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

@@ -1153,11 +1153,11 @@ struct PaintSkew
 
   void paint_glyph (hb_paint_context_t *c, uint32_t varIdxBase) const
   {
-    float x = +tanf (xSkewAngle.to_float(c->instancer (varIdxBase, 0)) * (float) M_PI);
-    float y = -tanf (ySkewAngle.to_float(c->instancer (varIdxBase, 1)) * (float) M_PI);
-    c->funcs->push_transform (c->data, 1., y, x, 1., 0., 0.);
+    float sx = xSkewAngle.to_float(c->instancer (varIdxBase, 0));
+    float sy = ySkewAngle.to_float(c->instancer (varIdxBase, 1));
+    c->funcs->push_skew (c->data, sx, sy);
     c->recurse (this+src);
-    c->funcs->pop_transform (c->data);
+    c->funcs->pop_skew (c->data, sx, sy);
   }
 
   HBUINT8		format; /* format = 28(noVar) or 29 (Var) */
@@ -1189,16 +1189,16 @@ struct PaintSkewAroundCenter
 
   void paint_glyph (hb_paint_context_t *c, uint32_t varIdxBase) const
   {
-    float x = +tanf (xSkewAngle.to_float(c->instancer (varIdxBase, 0)) * (float) M_PI);
-    float y = -tanf (ySkewAngle.to_float(c->instancer (varIdxBase, 1)) * (float) M_PI);
+    float sx = xSkewAngle.to_float(c->instancer (varIdxBase, 0));
+    float sy = ySkewAngle.to_float(c->instancer (varIdxBase, 1));
     float tCenterX = centerX + c->instancer (varIdxBase, 2);
     float tCenterY = centerY + c->instancer (varIdxBase, 3);
     c->funcs->push_translate (c->data, +tCenterX, +tCenterY);
-    c->funcs->push_transform (c->data, 1., y, x, 1., 0., 0.);
+    c->funcs->push_skew (c->data, sx, sy);
     c->funcs->push_translate (c->data, -tCenterX, -tCenterY);
     c->recurse (this+src);
     c->funcs->pop_translate (c->data, -tCenterX, -tCenterY);
-    c->funcs->pop_transform (c->data);
+    c->funcs->pop_skew (c->data, sx, sy);
     c->funcs->pop_translate (c->data, +tCenterX, +tCenterY);
   }
 

src/hb-paint.hh

@@ -218,6 +218,23 @@ struct hb_paint_funcs_t
     if (a)
       pop_transform (paint_data);
   }
+
+  void push_skew (void *paint_data,
+                  float sx, float sy)
+  {
+    if (sx || sy)
+    {
+      float x = +tanf (sx * (float) M_PI);
+      float y = -tanf (sy * (float) M_PI);
+      push_transform (paint_data, 1.f, y, x, 1.f, 0.f, 0.f);
+    }
+  }
+  void pop_skew (void *paint_data,
+                  float sx, float sy)
+  {
+    if (sx || sy)
+      pop_transform (paint_data);
+  }
 };
 DECLARE_NULL_INSTANCE (hb_paint_funcs_t);