Fixing numerical rounding edge case in SkTileGrid

tests/TileGridTest.cpp

 
 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 #include "SkTileGrid.h"
@@ skipping 160 matching lines @@
         canvas->drawRect(rect2, paint);
         canvas->drawRect(rect3, paint);
         picture.endRecording();
 
         SkBitmap tileBitmap;
         tileBitmap.setConfig(SkBitmap::kARGB_8888_Config, 10, 10);
         tileBitmap.allocPixels();
         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
             // So a look-up at interval 0-10 should be grid aligned,
             SkDevice device(tileBitmap);
             MockCanvas mockCanvas(&device);
             picture.draw(&mockCanvas);
             REPORTER_ASSERT(reporter, 1 == mockCanvas.fRects.count());
             REPORTER_ASSERT(reporter, rect1 == mockCanvas.fRects[0]);
         }
@@ skipping 28 matching lines @@
         }
         {
             SkDevice device(tileBitmap);
             MockCanvas mockCanvas(&device);
             mockCanvas.translate(SkFloatToScalar(-8.1f), SkFloatToScalar(-8.1f));
             picture.draw(&mockCanvas);
             REPORTER_ASSERT(reporter, 2 == mockCanvas.fRects.count());
             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) {
         // Out of bounds
         verifyTileHits(reporter, SkIRect::MakeXYWH(30, 0, 1, 1),  0);
         verifyTileHits(reporter, SkIRect::MakeXYWH(0, 30, 1, 1),  0);
         verifyTileHits(reporter, SkIRect::MakeXYWH(-10, 0, 1, 1),  0);
         verifyTileHits(reporter, SkIRect::MakeXYWH(0, -10, 1, 1),  0);
 
         // Dilation for AA consideration
@@ skipping 18 matching lines @@
         verifyTileHits(reporter, SkIRect::MakeXYWH(-10, -10, 40, 40),  kAll_Tile);
 
         TestUnalignedQuery(reporter);
         TestOverlapOffsetQueryAlignment(reporter);
     }
 };
 
 
 #include "TestClassDef.h"
 DEFINE_TESTCLASS("TileGrid", TileGridTestClass, TileGridTest::Test)