Fixing SkTileGrid to clamp rather than clip content and querries that are outside the bounds of the…

src/core/SkTileGrid.cpp

Index: src/core/SkTileGrid.cpp
===================================================================
--- src/core/SkTileGrid.cpp	(revision 8533)
+++ src/core/SkTileGrid.cpp	(working copy)
@@ -39,9 +39,6 @@
     SkIRect dilatedBounds = bounds;
     dilatedBounds.outset(fInfo.fMargin.width(), fInfo.fMargin.height());
     dilatedBounds.offset(fInfo.fOffset);
-    if (!SkIRect::Intersects(dilatedBounds, fGridBounds)) {

[Tom Hudson, 2013/04/09 10:10:50]

Either this code was erroneous, or the new version could end up not adding data
to any tile, right? Something smells wrong here.

-        return;
-    }
 
     // Note: SkIRects are non-inclusive of the right() column and bottom() row,
     // hence the "-1"s in the computations of maxTileX and maxTileY.
@@ -75,16 +72,14 @@
     int tileStartY = adjustedQuery.top() / fInfo.fTileInterval.height();
     int tileEndY = (adjustedQuery.bottom() + fInfo.fTileInterval.height() - 1) /
         fInfo.fTileInterval.height();
-    if (tileStartX >= fXTileCount || tileStartY >= fYTileCount || tileEndX <= 0 || tileEndY <= 0) {
-        return; // query does not intersect the grid
-    }
-    // clamp to grid
-    if (tileStartX < 0) tileStartX = 0;
-    if (tileStartY < 0) tileStartY = 0;
-    if (tileEndX > fXTileCount) tileEndX = fXTileCount;
-    if (tileEndY > fYTileCount) tileEndY = fYTileCount;
 
+    tileStartX = SkClampMinMax(tileStartX, 0, fXTileCount - 1);
+    tileEndX = SkClampMinMax(tileEndX, 1, fXTileCount);
+    tileStartY = SkClampMinMax(tileStartY, 0, fYTileCount - 1);
+    tileEndY = SkClampMinMax(tileEndY, 1, fYTileCount);
+
     int queryTileCount = (tileEndX - tileStartX) * (tileEndY - tileStartY);
+    SkASSERT(queryTileCount);
     if (queryTileCount == 1) {
         *results = this->tile(tileStartX, tileStartY);
     } else {