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experimental/skpdiff/SkDifferentPixelsMetric_opencl.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 
 #include "SkDifferentPixelsMetric.h"
 #include "skpdiff_util.h"
 
 static const char kDifferentPixelsKernelSource[] =
     "#pragma OPENCL_EXTENSION cl_khr_global_int32_base_atomics                  \n"
     "                                                                           \n"
     "const sampler_t gInSampler = CLK_NORMALIZED_COORDS_FALSE |                 \n"
     "                             CLK_ADDRESS_CLAMP_TO_EDGE   |                 \n"
     "                             CLK_FILTER_NEAREST;                           \n"
     "                                                                           \n"
     "__kernel void diff(read_only image2d_t baseline, read_only image2d_t test, \n"
     "                   __global int* result, __global int2* poi) {             \n"
     "    int2 coord = (int2)(get_global_id(0), get_global_id(1));               \n"
     "    uint4 baselinePixel = read_imageui(baseline, gInSampler, coord);       \n"
     "    uint4 testPixel = read_imageui(test, gInSampler, coord);               \n"
-    "    int4 pixelCompare = baselinePixel == testPixel;                        \n"
     "    if (baselinePixel.x != testPixel.x ||                                  \n"
     "        baselinePixel.y != testPixel.y ||                                  \n"
     "        baselinePixel.z != testPixel.z ||                                  \n"
     "        baselinePixel.w != testPixel.w) {                                  \n"
     "                                                                           \n"
     "        int poiIndex = atomic_inc(result);                                 \n"
     "        poi[poiIndex] = coord;                                             \n"
     "    }                                                                      \n"
     "}                                                                          \n";
 
@@ skipping 77 matching lines @@
     // This makes things totally synchronous. Actual queue is not ready yet
     clWaitForEvents(1, &event);
     diff->finished = true;
 
     // Immediate read back the results
     clEnqueueReadBuffer(fCommandQueue, diff->resultsBuffer, CL_TRUE, 0,
                         sizeof(int), &diff->numDiffPixels, 0, NULL, NULL);
     diff->result *= (double)diff->numDiffPixels;
     diff->result = (1.0 - diff->result);
 
-    diff->poi = SkNEW_ARRAY(SkIPoint, diff->numDiffPixels);
-    clEnqueueReadBuffer(fCommandQueue, diff->poiBuffer, CL_TRUE, 0,
+    // Reading a buffer of size zero can cause issues on some (Mac) OpenCL platforms.
+    if (diff->numDiffPixels > 0) {
+        diff->poi = SkNEW_ARRAY(SkIPoint, diff->numDiffPixels);
+        clEnqueueReadBuffer(fCommandQueue, diff->poiBuffer, CL_TRUE, 0,
                         sizeof(SkIPoint) * diff->numDiffPixels, diff->poi, 0, NULL, NULL);
+    }
 
     // Release all the buffers created
     clReleaseMemObject(diff->poiBuffer);
     clReleaseMemObject(diff->resultsBuffer);
     clReleaseMemObject(diff->baseline);
     clReleaseMemObject(diff->test);
 
     SkDebugf("Time: %f\n", (get_seconds() - startTime));
 
     return diffID;
@@ skipping 23 matching lines @@
     return fQueuedDiffs[id].poi;
 }
 
 bool SkDifferentPixelsMetric::onInit() {
     if (!this->loadKernelSource(kDifferentPixelsKernelSource, "diff", &fKernel)) {
         return false;
     }
 
     return true;
 }