Clarify bmp comment about when we support the alpha mask

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1689183002

Review URL: https://codereview.chromium.org/1689183002
This commit is contained in:
msarett 2016-02-11 08:41:53 -08:00 committed by Commit bot
parent 4946b9419f
commit ef02b24d1c

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@ -373,9 +373,13 @@ bool SkBmpCodec::ReadHeader(SkStream* stream, bool inIco, SkCodec** codecOut) {
// of the image to use the alpha channels. However, many of these images
// leave the alpha channel blank and expect to be rendered as opaque. This
// is the case for almost all V3 images, so we render these as opaque. For
// V4+, we will use the alpha channel, and fix the image later if it turns
// out to be fully transparent.
// As an exception, V3 bmp-in-ico may use an alpha mask.
// V4+ images in kMask mode, we will use the alpha mask.
//
// skbug.com/4116: We should perhaps also apply the alpha mask in kStandard
// mode. We just haven't seen any images that expect this
// behavior.
//
// Additionally, V3 bmp-in-ico may use the alpha mask.
SkAlphaType alphaType = kOpaque_SkAlphaType;
if ((kInfoV3_BmpHeaderType == headerType && inIco) ||
kInfoV4_BmpHeaderType == headerType ||