Correct gesture scale and translation

tools/viewer/Viewer.cpp

Index: tools/viewer/Viewer.cpp
diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index d492cdeefeb854246b90d5e721cfa43c28662cb9..82c28ae9b1843b46fda2de7da5e1842d116fd7d8 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -190,6 +190,9 @@ void Viewer::updateTitle() {
 }
 
 void Viewer::setupCurrentSlide(int previousSlide) {
+    fGesture.reset();
+    fOffsetMatrix.reset();
+    fPreTouchMatrix.reset();
     this->updateTitle();
     fSlides[fCurrentSlide]->load();
     if (previousSlide >= 0) {
@@ -230,8 +233,44 @@ SkMatrix Viewer::computeMatrix() {
         m.postTranslate(cx, cy);
     }
 
-    m.preConcat(fGesture.localM());
-    m.preConcat(fGesture.globalM());
+    SkMatrix touchMatrixWithOffset;

[djsollen, 2016/05/19 17:04:23]

I think you can do this computation by just applying the gesture matrix to m. 
Then just look at the current scale and translate on the matrix and if it would
cause the content to be scrolled off the screen then just translate it back onto
the screen.

[liyuqian, 2016/05/19 19:23:15]

Done.

+    touchMatrixWithOffset.reset();
+    touchMatrixWithOffset.postConcat(fGesture.globalM());
+    touchMatrixWithOffset.postConcat(fGesture.localM());
+    if (touchMatrixWithOffset.isIdentity()) {
+        // The touch gesture has reset the matrix, so we reset the offset too.
+        fOffsetMatrix.reset();
+    }
+    touchMatrixWithOffset.preConcat(fOffsetMatrix);
+
+    // Begin checking if more offset is needed
+
+    const SkScalar scaleX = touchMatrixWithOffset.getScaleX();
+    const SkScalar scaleY = touchMatrixWithOffset.getScaleY();
+    // Bring the X/Y translation to the slide's scale
+    const SkScalar tX = touchMatrixWithOffset.getTranslateX() / scaleX;
+    const SkScalar tY = touchMatrixWithOffset.getTranslateY() / scaleY;
+
+    const SkISize slideSize = fSlides[fCurrentSlide]->getDimensions();
+    const SkScalar SW = slideSize.width(), SH = slideSize.height(), ZERO = 0;
+
+    // Bring contentRect's widht/height to the slide's scale
+    const SkRect contentRect = fWindow->getContentRect();

[djsollen, 2016/05/19 17:04:23]

on windows that don't return true for supportsContentRect() this will return an
empty rect.

[liyuqian, 2016/05/19 19:23:15]

Done.

+    const SkScalar CW = contentRect.width() / fPreTouchMatrix.getScaleX() / scaleX;
+    const SkScalar CH = contentRect.height() / fPreTouchMatrix.getScaleY() / scaleY;
+
+    // X Translation could be no less than -SW and no more than CW
+    const SkScalar overX = std::min(ZERO, tX + SW) + std::max(ZERO, tX - CW);
+    // Y Translation is similar to the X translation
+    const SkScalar overY = std::min(ZERO, tY + SH) + std::max(ZERO, tY - CH);
+
+    // Apply additional offset
+    fOffsetMatrix.preTranslate(-overX * scaleX, -overY * scaleY);
+    touchMatrixWithOffset.preTranslate(-overX * scaleX, -overY * scaleY);
+
+    // Finished checking offset
+
+    m.preConcat(touchMatrixWithOffset);
 
     return m;
 }
@@ -252,8 +291,9 @@ void Viewer::onPaint(SkCanvas* canvas) {
         const SkISize slideSize = fSlides[fCurrentSlide]->getDimensions();
         const SkRect slideBounds = SkRect::MakeIWH(slideSize.width(), slideSize.height());
         SkMatrix matrix;
-        matrix.setRectToRect(slideBounds, contentRect, SkMatrix::kCenter_ScaleToFit);
+        matrix.setRectToRect(slideBounds, contentRect, SkMatrix::kStart_ScaleToFit);
         canvas->concat(matrix);
+        fPreTouchMatrix = matrix;
     }
     canvas->concat(computeMatrix());
 
@@ -268,17 +308,19 @@ void Viewer::onPaint(SkCanvas* canvas) {
 
 bool Viewer::onTouch(int owner, Window::InputState state, float x, float y) {
     void* castedOwner = reinterpret_cast<void*>(owner);
+    float castedX = (x - fPreTouchMatrix.getTranslateX()) / fPreTouchMatrix.getScaleX();
+    float castedY = (y - fPreTouchMatrix.getTranslateY()) / fPreTouchMatrix.getScaleY();

[djsollen, 2016/05/19 17:04:23]

SkPoint touchPoint = SkPoint::Make(x, y);
SkMatrix::mapPoints(&touchPoint, 1);

[liyuqian, 2016/05/19 19:23:15]

Done.

     switch (state) {
         case Window::kUp_InputState: {
             fGesture.touchEnd(castedOwner);
             break;
         }
         case Window::kDown_InputState: {
-            fGesture.touchBegin(castedOwner, x, y);
+            fGesture.touchBegin(castedOwner, castedX, castedY);
             break;
         }
         case Window::kMove_InputState: {
-            fGesture.touchMoved(castedOwner, x, y);
+            fGesture.touchMoved(castedOwner, castedX, castedY);
             break;
         }
     }