Fixing numerical rounding edge case in SkTileGrid

BUG=https://code.google.com/p/chromium/issues/detail?id=234688
TEST=TileGrid skia unit test

Review URL: https://codereview.chromium.org/13860011

git-svn-id: http://skia.googlecode.com/svn/trunk@8839 2bbb7eff-a529-9590-31e7-b0007b416f81

diff --git a/src/core/SkTileGrid.cpp b/src/core/SkTileGrid.cpp
index 7a9c8ee..c39e21b 100644 (file)
--- a/src/core/SkTileGrid.cpp
+++ b/src/core/SkTileGrid.cpp
@@ -81,9 +81,9 @@ void SkTileGrid::search(const SkIRect& query, SkTDArray<void*>* results) {
         fInfo.fTileInterval.height();
 
     tileStartX = SkPin32(tileStartX, 0, fXTileCount - 1);
-    tileEndX = SkPin32(tileEndX, 1, fXTileCount);
+    tileEndX = SkPin32(tileEndX, tileStartX+1, fXTileCount);
     tileStartY = SkPin32(tileStartY, 0, fYTileCount - 1);
-    tileEndY = SkPin32(tileEndY, 1, fYTileCount);
+    tileEndY = SkPin32(tileEndY, tileStartY+1, fYTileCount);
 
     int queryTileCount = (tileEndX - tileStartX) * (tileEndY - tileStartY);
     SkASSERT(queryTileCount);

diff --git a/tests/TileGridTest.cpp b/tests/TileGridTest.cpp
index 78620b4..e409afd 100644 (file)
--- a/tests/TileGridTest.cpp
+++ b/tests/TileGridTest.cpp
@@ -178,6 +178,9 @@ public:
         SkBitmap moreThanATileBitmap;
         moreThanATileBitmap.setConfig(SkBitmap::kARGB_8888_Config, 11, 11);
         moreThanATileBitmap.allocPixels();
+        SkBitmap tinyBitmap;
+        tinyBitmap.setConfig(SkBitmap::kARGB_8888_Config, 2, 2);
+        tinyBitmap.allocPixels();
         // Test parts of top-left tile
         {
             // The offset should cancel the top and left borders of the top left tile
@@ -226,6 +229,20 @@ public:
             REPORTER_ASSERT(reporter, rect2 == mockCanvas.fRects[0]);
             REPORTER_ASSERT(reporter, rect3 == mockCanvas.fRects[1]);
         }
+        {
+            // Regression test for crbug.com/234688
+            // Once the 2x2 device region is inset by margin, it yields an empty
+            // adjusted region, sitting right on top of the tile boundary.
+            SkDevice device(tinyBitmap);
+            MockCanvas mockCanvas(&device);
+            mockCanvas.translate(SkFloatToScalar(-8.0f), SkFloatToScalar(-8.0f));
+            picture.draw(&mockCanvas);
+            // This test passes by not asserting. We do not validate the rects recorded
+            // because the result is numerically unstable (floating point equality). 
+            // The content of any one of the four tiles of the tilegrid would be a valid
+            // result since any bbox that covers the center point of the canvas will be
+            // recorded in all four tiles.
+        }
     }
 
     static void Test(skiatest::Reporter* reporter) {