Factor code to rotate a canvas about a point.

src/core/SkCanvas.cpp

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapDevice.h"
 #include "SkCanvas.h"
 #include "SkCanvasPriv.h"
@@ skipping 1480 matching lines @@
     m.setScale(sx, sy);
     this->concat(m);
 }
 
 void SkCanvas::rotate(SkScalar degrees) {
     SkMatrix m;
     m.setRotate(degrees);
     this->concat(m);
 }
 
+void SkCanvas::rotate(SkScalar degrees, SkScalar px, SkScalar py) {

[reed1, 2016/07/12 17:28:59]

possibly check for 0 == degrees to skip the rest. Just a thought.

[bungeman-skia, 2016/07/12 17:37:42]

If so, I think it would need to be done above as well. If you think it would be
common enough to be interesting, we can put together a CL to do that.

It turns out that this is already better than the translate-rotate-translate
calls from Patch Set 1, since the matrix is being produced more efficiently and
there is only one concat (as opposed to three concats).

+    SkMatrix m;
+    m.setRotate(degrees, px, py);
+    this->concat(m);
+}
+
 void SkCanvas::skew(SkScalar sx, SkScalar sy) {
     SkMatrix m;
     m.setSkew(sx, sy);
     this->concat(m);
 }
 
 void SkCanvas::concat(const SkMatrix& matrix) {
     if (matrix.isIdentity()) {
         return;
     }
@@ skipping 1611 matching lines @@
 
 SkAutoCanvasMatrixPaint::~SkAutoCanvasMatrixPaint() {
     fCanvas->restoreToCount(fSaveCount);
 }
 
 #ifdef SK_SUPPORT_LEGACY_NEW_SURFACE_API
 SkSurface* SkCanvas::newSurface(const SkImageInfo& info, const SkSurfaceProps* props) {
     return this->makeSurface(info, props).release();
 }
 #endif