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)
@@ -66,6 +66,7 @@
     SkIRect adjustedQuery = query;
     adjustedQuery.inset(fInfo.fMargin.width(), fInfo.fMargin.height());
     adjustedQuery.offset(fInfo.fOffset);
+    adjustedQuery.sort(); // in case the inset inverted the rectangle

[reed1, 2013/04/09 15:56:16]

If we might invert, then (I presume) we are making the query rect smaller (by
fMargin). Why is that? Naively I would have guessed we would, if anything,
enlarge the query rect, to be conservative in which items we return...

     // Convert the query rectangle from device coordinates to tile coordinates
     // by rounding outwards to the nearest tile boundary so that the resulting tile
     // region includes the query rectangle. (using truncating division to "floor")
@@ -75,16 +76,14 @@
     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 = SkPin32(tileStartX, 0, fXTileCount - 1);
+    tileEndX = SkPin32(tileEndX, 1, fXTileCount);
+    tileStartY = SkPin32(tileStartY, 0, fYTileCount - 1);
+    tileEndY = SkPin32(tileEndY, 1, fYTileCount);
+
     int queryTileCount = (tileEndX - tileStartX) * (tileEndY - tileStartY);
+    SkASSERT(queryTileCount);
     if (queryTileCount == 1) {
         *results = this->tile(tileStartX, tileStartY);
     } else {