Do not fail on images that are too small to subset decode

dm/DMSrcSink.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "DMSrcSink.h"
 #include "SamplePipeControllers.h"
 #include "SkCodec.h"
@@ skipping 164 matching lines @@
                 }
             }
             canvas->drawBitmap(bitmap, 0, 0);
             break;
         }
         case kScanline_Subset_Mode: {
             //this mode decodes the image in divisor*divisor subsets, using a scanline decoder
             const int divisor = 2;
             const int w = decodeInfo.width();
             const int h = decodeInfo.height();
-            if (w*h == 1) {
-                return Error::Nonfatal("Subset decoding not supported.");
-            }
             if (divisor > w || divisor > h) {
-                return SkStringPrintf("divisor %d is too big for %s with dimensions (%d x %d)",
-                        divisor, fPath.c_str(), w, h);
+                return Error::Nonfatal(SkStringPrintf("Cannot decode subset: divisor %d is too big"
+                        "for %s with dimensions (%d x %d)", divisor, fPath.c_str(), w, h));
             }
             const int subsetWidth = w/divisor;
             const int subsetHeight = h/divisor;
             // One of our subsets will be larger to contain any pixels that do not divide evenly.
             const int extraX = w % divisor;
             const int extraY = h % divisor;
             /*
             * if w or h are not evenly divided by divisor need to adjust width and height of end
             * subsets to cover entire image.
             * Add extraX and extraY to largestSubsetBm's width and height to adjust width
@@ skipping 199 matching lines @@
         return "";
     }
     // Decode subsets.  This is a little involved.
     SkAutoTDelete<SkMemoryStream> stream(new SkMemoryStream(encoded));
     SkAutoTDelete<SkImageDecoder> decoder(SkImageDecoder::Factory(stream.get()));
     if (!decoder) {
         return SkStringPrintf("Can't find a good decoder for %s.", fPath.c_str());
     }
     stream->rewind();
     int w,h;
-    if (!decoder->buildTileIndex(stream.detach(), &w, &h) || w*h == 1) {
+    if (!decoder->buildTileIndex(stream.detach(), &w, &h)) {
         return Error::Nonfatal("Subset decoding not supported.");
     }
 
     // Divide the image into subsets that cover the entire image.
     if (fDivisor > w || fDivisor > h) {
-        return SkStringPrintf("divisor %d is too big for %s with dimensions (%d x %d)",
-                              fDivisor, fPath.c_str(), w, h);
+        return Error::Nonfatal(SkStringPrintf("Cannot decode subset: divisor %d is too big"
+                "for %s with dimensions (%d x %d)", fDivisor, fPath.c_str(), w, h));
     }
     const int subsetWidth  = w / fDivisor,
               subsetHeight = h / fDivisor;
     for (int y = 0; y < h; y += subsetHeight) {
         for (int x = 0; x < w; x += subsetWidth) {
             SkBitmap subset;
             SkIRect rect = SkIRect::MakeXYWH(x, y, subsetWidth, subsetHeight);
             if (!decoder->decodeSubset(&subset, rect, dstColorType)) {
                 return SkStringPrintf("Could not decode subset (%d, %d, %d, %d).",
                                       x, y, x+subsetWidth, y+subsetHeight);
@@ skipping 542 matching lines @@
             skr.visit<void>(i, drawsAsSingletonPictures);
         }
         SkAutoTUnref<SkPicture> macroPic(macroRec.endRecordingAsPicture());
 
         canvas->drawPicture(macroPic);
         return "";
     });
 }
 
 }  // namespace DM