Factor code to rotate a canvas about a point.

gm/dftext.cpp

 /*
  * Copyright 2011 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 "Resources.h"
 #include "SkCanvas.h"
 #include "SkStream.h"
@@ skipping 15 matching lines @@
     SkString onShortName() override {
         SkString name("dftext");
         name.append(sk_tool_utils::platform_os_emoji());
         return name;
     }
 
     SkISize onISize() override {
         return SkISize::Make(1024, 768);
     }
 
-    static void rotate_about(SkCanvas* canvas,
-        SkScalar degrees,
-        SkScalar px, SkScalar py) {
-        canvas->translate(px, py);
-        canvas->rotate(degrees);
-        canvas->translate(-px, -py);
-    }
-
     virtual void onDraw(SkCanvas* inputCanvas) override {
         SkScalar textSizes[] = { 9.0f, 9.0f*2.0f, 9.0f*5.0f, 9.0f*2.0f*5.0f };
         SkScalar scales[] = { 2.0f*5.0f, 5.0f, 2.0f, 1.0f };
 
         // set up offscreen rendering with distance field text
 #if SK_SUPPORT_GPU
         GrContext* ctx = inputCanvas->getGrContext();
         SkISize size = onISize();
         SkImageInfo info = SkImageInfo::MakeN32(size.width(), size.height(), kPremul_SkAlphaType,
                                                 sk_ref_sp(inputCanvas->imageInfo().colorSpace()));
@@ skipping 34 matching lines @@
             y += paint.getFontMetrics(nullptr)*scales[i];
         }
 
         // check rotation
         for (size_t i = 0; i < 5; ++i) {
             SkScalar rotX = SkIntToScalar(10);
             SkScalar rotY = y;
 
             SkAutoCanvasRestore acr(canvas, true);
             canvas->translate(SkIntToScalar(10 + i * 200), -80);
-            rotate_about(canvas, SkIntToScalar(i * 5), rotX, rotY);
+            canvas->rotate(SkIntToScalar(i * 5), rotX, rotY);
             for (int ps = 6; ps <= 32; ps += 3) {
                 paint.setTextSize(SkIntToScalar(ps));
                 canvas->drawText(text, textLen, rotX, rotY, paint);
                 rotY += paint.getFontMetrics(nullptr);
             }
         }
 
         // check scaling down
         paint.setLCDRenderText(true);
         x = SkIntToScalar(680);
@@ skipping 102 matching lines @@
     }
 
 private:
     sk_sp<SkTypeface> fEmojiTypeface;
     const char* fEmojiText;
 
     typedef skiagm::GM INHERITED;
 };
 
 DEF_GM(return new DFTextGM;)