cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   Niuis
   Member

   Hello,

   I read the threads about the premultiplied alpha and the png compression but I was not able to find a solution to my problem.

   If I draw a circle using photoshop or any other tools (I tried others to be sure it was not a superPNG plugin issue) on a transparent background, the last line of pixel is not displayed, it is way more aliased and some pixels are clamped.
   I checked and I don't have any exotic glAlphaFunc hidden somewhere for example.

   If I replace the transparent background in my png by an opaque color, everything is working fine and my circle is very smooth.
   But as soon as I am back on exporting my png with a transparent background, my circle is very aliased, as if the alpha was exported as 1 bit.
   My png is exported as a 24 bits png though.

   I tried using the same png with UIImage and it is displayed properly, with a smooth edge, so it really seems to be related to the texture2D behavior.

   I also tried
   [[Director sharedDirector] setPixelFormat:kRGBA8];
   [Texture2D setDefaultAlphaPixelFormat:kTexture2DPixelFormat_RGBA8888];

   I load the circle as a sprite, without any scale, with an opacity of 255.
   The image is a 64x64, to avoid power of 2 issues.

   Any ideas? Am I missing something obvious?

   Posted 2 years ago #
2. 

   michaelm
   Member

   The 24 bit export could be the problem. Not sure how they are packing the bits but usually 1 byte for each component or 32 bits per pixel. So you would be losing a little precision off of each color component to create a small alpha channel.

   Just use 32 bit export, It will only affect disk size and not by much, size in memory in use won't be affected. And the problem should go away.

   Posted 2 years ago #
3. 

   renderplace
   Member

   @Niuis, I wrote similar in other thread. I had some similar issue when upgrading from cocos2d v0.7.3 --> v0.8.2

   In my case the problem completely gone when applying these two fixes on top of cocos2d v0.8.2:

   http://code.google.com/p/cocos2d-iphone/source/diff?spec=svn1656&r=1656&format=side&path=/trunk/cocos2d/CCTexture2D.m

   http://code.google.com/p/cocos2d-iphone/source/diff?spec=svn1651&r=1651&format=side&path=/trunk/cocos2d/CCTexture2D.m

   Found via http://code.google.com/p/cocos2d-iphone/issues/detail?id=697

   Not sure if you're having the same problem, but it might be worth to look at.

   -AntonG

   Posted 2 years ago #
4. 

   Niuis
   Member

   Thanks for your answers!

   I tried the 32 bits export and Texture2D patch but I keep having the same problem.

   I also tried to force the min and mag filters to nearest instead of linear and I have slightly better results: the border is sharper and closest to what it looks under photoshop.

   However, I still not have a smooth border and the alpha looks like it lacks of accuracy.

   Maybe an image can help:
   The first image is how it looks under photoshop
   The second image is a capture from the device

   If the pictures are not clear enough, just look the 4x4 upper right square, clearly darker on the second pictures.

   
   

   I tried with other colors and the border is always larger than it should be, as if the alpha values were bigger than what I expect.

   Posted 2 years ago #
5. 

   Niuis
   Member

   Last update: if I create a small application from scratch without using cocos, but using texture2D, the image works properly, smooth and with the same alpha as in photoshop.

   What OpenGL state(s) could be changed by cocos and I could try to reset?
   I am only using sprites and label atlas when my results are incorrect.

   Posted 2 years ago #
6. 

   riq
   Key Master

   what cocos2d version are you using ?

   Posted 2 years ago #
7. 

   Niuis
   Member

   I am using the 0.8.2 version

   Posted 2 years ago #

RSS feed for this topic

Reply

You must log in to post.