Force tiles in SampleApp to integer boundaries.

samplecode/SampleApp.cpp

Index: samplecode/SampleApp.cpp
diff --git a/samplecode/SampleApp.cpp b/samplecode/SampleApp.cpp
index 7ebac5f2151867e6d9604e9725cd08c80fe87785..6d5f647b158cee1df0baa5f8138a1afba6845474 100644
--- a/samplecode/SampleApp.cpp
+++ b/samplecode/SampleApp.cpp
@@ -876,7 +876,6 @@ SampleWindow::SampleWindow(void* hwnd, int argc, char** argv, DeviceManager* dev
     fHintingState = 0;
     fFilterQualityIndex = 0;
     fFlipAxis = 0;
-    fScrollTestX = fScrollTestY = 0;
 
     fMouseX = fMouseY = 0;
     fFatBitsScale = 8;
@@ -885,6 +884,7 @@ SampleWindow::SampleWindow(void* hwnd, int argc, char** argv, DeviceManager* dev
 
     fZoomLevel = 0;
     fZoomScale = SK_Scalar1;
+    fOffset = { 0, 0 };
 
     fMagnify = false;
 
@@ -1062,14 +1062,14 @@ void SampleWindow::draw(SkCanvas* canvas) {
     if (kNo_Tiling == fTilingMode) {
         this->INHERITED::draw(canvas); // no looping or surfaces needed
     } else {
-        const int w = SkScalarRoundToInt(tile.width());
-        const int h = SkScalarRoundToInt(tile.height());
-        SkImageInfo info = SkImageInfo::MakeN32Premul(w, h);
+        const SkScalar w = SkScalarCeilToScalar(tile.width());
+        const SkScalar h = SkScalarCeilToScalar(tile.height());
+        SkImageInfo info = SkImageInfo::MakeN32Premul(SkScalarTruncToInt(w), SkScalarTruncToInt(h));
         SkAutoTUnref<SkSurface> surface(canvas->newSurface(info));
         SkCanvas* tileCanvas = surface->getCanvas();
 
-        for (SkScalar y = 0; y < height(); y += tile.height()) {
-            for (SkScalar x = 0; x < width(); x += tile.width()) {
+        for (SkScalar y = 0; y < height(); y += h) {
+            for (SkScalar x = 0; x < width(); x += w) {
                 SkAutoCanvasRestore acr(tileCanvas, true);
                 tileCanvas->translate(-x, -y);

[bungeman-skia, 2016/03/03 22:42:37]

Just to make things more clear, when x and y are not integers this means that
the pixel at the origin of the canvas is no longer at an integer position. Every
calculation will be shifted by the fractional part, resulting in rounding being
out of phase from the rounding if the same were drawn with a slightly different
fractional part.

                 tileCanvas->clear(0);
@@ -1462,6 +1462,11 @@ void SampleWindow::beforeChild(SkView* child, SkCanvas* canvas) {
     }
 }
 
+void SampleWindow::changeOffset(SkVector delta) {
+    fOffset += delta;
+    this->updateMatrix();
+}
+
 void SampleWindow::changeZoomLevel(float delta) {
     fZoomLevel += delta;
     if (fZoomLevel > 0) {
@@ -1479,6 +1484,7 @@ void SampleWindow::changeZoomLevel(float delta) {
 void SampleWindow::updateMatrix(){
     SkMatrix m;
     m.reset();
+
     if (fZoomLevel) {
         SkPoint center;
         //m = this->getLocalMatrix();//.invert(&m);
@@ -1491,6 +1497,8 @@ void SampleWindow::updateMatrix(){
         m.postTranslate(cx, cy);
     }
 
+    m.postTranslate(fOffset.fX, fOffset.fY);
+
     if (fFlipAxis) {
         m.preTranslate(fZoomCenterX, fZoomCenterY);
         if (fFlipAxis & kFlipAxis_X) {
@@ -1685,13 +1693,7 @@ bool SampleWindow::onHandleChar(SkUnichar uni) {
     }
 
     if (0xFF != dx && 0xFF != dy) {
-        if ((dx | dy) == 0) {
-            fScrollTestX = fScrollTestY = 0;
-        } else {
-            fScrollTestX += dx;
-            fScrollTestY += dy;
-        }
-        this->inval(nullptr);
+        this->changeOffset({SkIntToScalar(dx / 32.0f), SkIntToScalar(dy / 32.0f)});
         return true;
     }
 
@@ -1855,6 +1857,10 @@ bool SampleWindow::onHandleKey(SkKey key) {
             }
         }
     }
+
+    int dx = 0xFF;
+    int dy = 0xFF;
+
     switch (key) {
         case kRight_SkKey:
             if (this->nextSample()) {
@@ -1882,9 +1888,26 @@ bool SampleWindow::onHandleKey(SkKey key) {
         case kBack_SkKey:
             this->showOverview();
             return true;
+
+        case k5_SkKey: dx =  0; dy =  0; break;
+        case k8_SkKey: dx =  0; dy = -1; break;
+        case k6_SkKey: dx =  1; dy =  0; break;
+        case k2_SkKey: dx =  0; dy =  1; break;
+        case k4_SkKey: dx = -1; dy =  0; break;
+        case k7_SkKey: dx = -1; dy = -1; break;
+        case k9_SkKey: dx =  1; dy = -1; break;
+        case k3_SkKey: dx =  1; dy =  1; break;
+        case k1_SkKey: dx = -1; dy =  1; break;
+
         default:
             break;
     }
+
+    if (0xFF != dx && 0xFF != dy) {
+        this->changeOffset({SkIntToScalar(dx / 32.0f), SkIntToScalar(dy / 32.0f)});
+        return true;
+    }
+
     return this->INHERITED::onHandleKey(key);
 }
 
@@ -2048,6 +2071,9 @@ void SampleWindow::updateTitle() {
     title.prepend(fFlipAxis & kFlipAxis_Y ? "Y " : nullptr);
     title.prepend(gHintingStates[fHintingState].label);
 
+    if (fOffset.fX || fOffset.fY) {
+        title.prependf("(%.2f, %.2f) ", SkScalarToFloat(fOffset.fX), SkScalarToFloat(fOffset.fY));
+    }
     if (fZoomLevel) {
         title.prependf("{%.2f} ", SkScalarToFloat(fZoomLevel));
     }