Support more color types for ICOs

src/codec/SkBmpCodec.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 "SkBmpCodec.h"
 #include "SkBmpMaskCodec.h"
 #include "SkBmpRLECodec.h"
@@ skipping 454 matching lines @@
     // We can do this here because there is no color table to read
     // in bit mask mode.
     if (!inIco && kBitMask_BmpInputFormat == inputFormat) {
         if (stream->skip(offset - bytesRead) != offset - bytesRead) {
             SkCodecPrintf("Error: unable to skip to image data.\n");
             return false;
         }
     }
 
     if (codecOut) {
+        // BMPs-in-ICOs contain an alpha mask after the image which means we
+        // cannot guarantee that an image is opaque, even if the bmp thinks
+        // it is.
+        bool isOpaque = kOpaque_SkAlphaType == alphaType;

[msarett, 2016/02/11 16:50:15]

Here we need to remember if the embedded BMP is actually opaque.  Since we will
always suggest kUnpremul for BMP-in-ICOs.

Another approach would be handle this in SkIcoCodec similar to how we did
before:

if (embeddedCodec is a bmp) {
    recommendedInfo = recommendedInfo.makeAlphaType(kUnpremul);
}

This would be simpler than the current code (no modifications to SkBmpCodec).

The drawback would be that we would print warnings on Ico decodes.
Ex: "BMP said it was opaque but is being decoded as if it is kUnpremul/Premul"

[scroggo, 2016/02/11 18:05:13]

This seems simple enough to me.

[msarett, 2016/02/11 18:15:47]

Acknowledged.

+        if (inIco) {
+            alphaType = kUnpremul_SkAlphaType;
+        }
+
         // Set the image info
         const SkImageInfo& imageInfo = SkImageInfo::Make(width, height,
                 colorType, alphaType);
 
         // Return the codec
         switch (inputFormat) {
             case kStandard_BmpInputFormat:
                 // We require streams to have a memory base for Bmp-in-Ico decodes.
                 SkASSERT(!inIco || nullptr != stream->getMemoryBase());
                 *codecOut = new SkBmpStandardCodec(imageInfo, stream, bitsPerPixel, numColors,
-                        bytesPerColor, offset - bytesRead, rowOrder, inIco);
+                        bytesPerColor, offset - bytesRead, rowOrder, isOpaque, inIco);
                 return true;
             case kBitMask_BmpInputFormat:
                 // Bmp-in-Ico must be standard mode
                 if (inIco) {
                     SkCodecPrintf("Error: Icos may not use bit mask format.\n");
                     return false;
                 }
 
                 *codecOut = new SkBmpMaskCodec(imageInfo, stream, bitsPerPixel, masks.detach(),
                         rowOrder);
@@ skipping 62 matching lines @@
     return prepareToDecode(dstInfo, options, inputColorPtr, inputColorCount);
 }
 
 int SkBmpCodec::onGetScanlines(void* dst, int count, size_t rowBytes) {
     // Create a new image info representing the portion of the image to decode
     SkImageInfo rowInfo = this->dstInfo().makeWH(this->dstInfo().width(), count);
 
     // Decode the requested rows
     return this->decodeRows(rowInfo, dst, rowBytes, this->options());
 }