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Fix bug: PremultipliedAlpha is not working for png #19112

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Fix bug: PremultipliedAlpha is not working for png #19112

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5 changes: 5 additions & 0 deletions cocos/platform/CCImage.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1149,6 +1149,11 @@ bool Image::initWithPngData(const unsigned char * data, ssize_t dataLen)
{
premultipliedAlpha();
}
else
{
_hasPremultipliedAlpha = true;
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@drelaptop drelaptop Oct 31, 2018

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Why enable premultipliedAlpha even png format isn't RGBA8888, any errors? maybe you use CCImage in wrong way.

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@chongchaoyu chongchaoyu Oct 31, 2018 •
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@drelaptop
oh, yes, if png format is not RGBA8888, premultipliedAlpha should not be true.

But, there is a case, I want to use PMA pngs to improve performance and prevent blend artifacts, so I use Image::setPNGPremultipliedAlphaEnabled(false), but it doesn't work, because CCImage.hasPremultipliedAlpha() will return false at Texture2D::initWithImage if you don't set premultipliedAlpha to true when png format is RGBA8888.

I will resubmit a PR, the code is like the followings:
1

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@chongchaoyu chongchaoyu Oct 31, 2018

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@drelaptop The new PR is #19138, you can check it.

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@drelaptop drelaptop Nov 1, 2018

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sorry, you hope CCImage.hasPremultipliedAlpha() return true, but you did setPNGPremultipliedAlphaEnabled(false) before. that is confusing.

no need to new a PR for same bug fix, you can commit to same branch, then PR will auto update.

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@chongchaoyu chongchaoyu Nov 1, 2018

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@drelaptop setPNGPremultipliedAlphaEnabled(false) changes PNG_PREMULTIPLIED_ALPHA_ENABLED to false, it tells cocos2dx that pngs have been PMAed by developers, so cocos2dx needn't to do premultipliedAlpha, premultipliedAlpha takes about 40ms for 2048*2048 pngs.

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@chongchaoyu chongchaoyu Nov 1, 2018

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@drelaptop I read CCImage.cpp, and setPNGPremultipliedAlphaEnabled(false) maybe the only way to use PMAed pngs.
Doesn't cocos2dx support PMAed pngs?
2

}


if (row_pointers != nullptr)
{
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