update path->rsxform to correctly interp dy

gm/drawatlas.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkCanvas.h"
 #include "SkRSXform.h"
@@ skipping 103 matching lines @@
 
     for (int i = 0; i < count; ++i) {
         SkPoint pos;
         SkVector tan;
         if (!meas.getPosTan(xy[i].x(), &pos, &tan)) {
             pos = xy[i];
             tan.set(1, 0);
         }
         xform[i].fSCos = tan.x();
         xform[i].fSSin = tan.y();
-        xform[i].fTx   = pos.x();
-        xform[i].fTy   = pos.y();
+        xform[i].fTx   = pos.x() - tan.y() * xy[i].y();
+        xform[i].fTy   = pos.y() + tan.x() * xy[i].y();
     }
 
     canvas->drawTextRSXform(text, length, &xform[0], nullptr, paint);
 }
 
-DEF_SIMPLE_GM(drawTextRSXform, canvas, 510, 310) {
-    const char text[] = "ABCDFGHJKLMNOPQRSTUVWXYZ";
-    const int N = sizeof(text) - 1;
+DEF_SIMPLE_GM(drawTextRSXform, canvas, 510, 370) {
+    const char text0[] = "ABCDFGHJKLMNOPQRSTUVWXYZ";
+    const char text1[] = "AAAAAAAAAAAAAAAAAAAAAAAAAA";
+    const int N = sizeof(text0) - 1;
     SkPoint pos[N];
     SkRSXform xform[N];
 
     canvas->translate(0, 30);
 
     SkScalar x = 20;
     SkScalar dx = 20;
     SkScalar rad = 0;
     SkScalar drad = 2 * SK_ScalarPI / (N - 1);
     for (int i = 0; i < N; ++i) {
         xform[i].fSCos = SkScalarCos(rad);
         xform[i].fSSin = SkScalarSin(rad);
         xform[i].fTx = x;
         xform[i].fTy = 0;
-        pos[i].set(x, 0);
+        pos[i].set(x, -10);
         x += dx;
         rad += drad;
     }
 
     SkPaint paint;
     paint.setAntiAlias(true);
     paint.setTextSize(20);
-    canvas->drawTextRSXform(text, N, xform, nullptr, paint);
+    canvas->drawTextRSXform(text0, N, xform, nullptr, paint);
 
     SkPath path;
-    path.addOval(SkRect::MakeXYWH(150, 50, 200, 200));
+    path.addOval(SkRect::MakeXYWH(150, 100, 200, 200));
 
-    draw_text_on_path_rigid(canvas, text, N, pos, path, paint);
+    draw_text_on_path_rigid(canvas, text1, N, pos, path, paint);
 
     paint.setStyle(SkPaint::kStroke_Style);
     canvas->drawPath(path, paint);
 }