Disable dithering in libjpeg-turbo for 565 decodes

tests/CodexTest.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 "Resources.h"
 #include "SkBitmap.h"
 #include "SkCodec.h"
@@ skipping 62 matching lines @@
         rect.sort();
     } while (rect.isEmpty());
     return rect;
 }
 
 static void check(skiatest::Reporter* r,
                   const char path[],
                   SkISize size,
                   bool supportsScanlineDecoding,
                   bool supportsSubsetDecoding,
                   bool supports565 = true) {

[scroggo, 2015/09/18 18:35:30]

Do all the callers just use the default value of true? Maybe remove this
variable?

(This came up because I wanted to make sure this test wasn't passing due to luck
- if the decode to 565 never happened, the redecode would not be interesting.)

[msarett, 2015/09/18 18:59:26]

We can almost remove this.

CMYK.jpg still needs to support 565.  I will remove this when I make that fix.

     SkAutoTDelete<SkStream> stream(resource(path));
     if (!stream) {
         SkDebugf("Missing resource '%s'\n", path);
         return;
     }
     SkAutoTDelete<SkCodec> codec(SkCodec::NewFromStream(stream.detach()));
     if (!codec) {
         ERRORF(r, "Unable to decode '%s'", path);
         return;
     }
 
     // This test is used primarily to verify rewinding works properly.  Using kN32 allows
     // us to test this without the added overhead of creating different bitmaps depending
     // on the color type (ex: building a color table for kIndex8).  DM is where we test
     // decodes to all possible destination color types.
     SkImageInfo info = codec->getInfo().makeColorType(kN32_SkColorType);
     REPORTER_ASSERT(r, info.dimensions() == size);
 
-    {
-        // Test decoding to 565
-        SkImageInfo info565 = info.makeColorType(kRGB_565_SkColorType);
-        SkCodec::Result expected = (supports565 && info.alphaType() == kOpaque_SkAlphaType) ?
-                SkCodec::kSuccess : SkCodec::kInvalidConversion;
-        test_info(r, codec, info565, expected, nullptr);
-    }
-
     SkBitmap bm;
     bm.allocPixels(info);
     SkAutoLockPixels autoLockPixels(bm);
     SkCodec::Result result =
         codec->getPixels(info, bm.getPixels(), bm.rowBytes(), nullptr, nullptr, nullptr);
     REPORTER_ASSERT(r, result == SkCodec::kSuccess);
 
     SkMD5::Digest digest;
     md5(bm, &digest);
 
-    // verify that re-decoding gives the same result.
+    {
+        // Test decoding to 565
+        SkImageInfo info565 = info.makeColorType(kRGB_565_SkColorType);
+        SkCodec::Result expected = (supports565 && info.alphaType() == kOpaque_SkAlphaType) ?
+                SkCodec::kSuccess : SkCodec::kInvalidConversion;
+        test_info(r, codec, info565, expected, nullptr);
+    }
+
+    // Verify that re-decoding gives the same result.  It is interesting to check this after
+    // a decode to 565, since choosing to decode to 565 may result in some of the decode
+    // options being modified.  These options should return to their defaults on another
+    // decode to kN32, so the new digest should match the old digest.
     test_info(r, codec, info, SkCodec::kSuccess, &digest);
 
     {
         // Check alpha type conversions
         if (info.alphaType() == kOpaque_SkAlphaType) {
             test_info(r, codec, info.makeAlphaType(kUnpremul_SkAlphaType),
                       SkCodec::kInvalidConversion, nullptr);
             test_info(r, codec, info.makeAlphaType(kPremul_SkAlphaType),
                       SkCodec::kInvalidConversion, nullptr);
         } else {
@@ skipping 256 matching lines @@
     REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
     result = decoder->start(
         decoder->getInfo().makeColorType(kIndex_8_SkColorType));
     REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
 }
 
 DEF_TEST(Codec_Params, r) {
     test_invalid_parameters(r, "index8.png");
     test_invalid_parameters(r, "mandrill.wbmp");
 }