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Opaque pixels

 
Ariel Ortiz
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The Sprite class API for MIDP 2.0 has three overridden methods called collidesWith that use the term "opaque pixels". I imagine that this term refers to non-transparent pixels that are available in PNG and GIF images. Can anyone tell me if this is correct?

...Ariel
 
Bert Bates
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Hmmm... Ariel,

I'd have to go poke around in the specs...have you done that? What have you found?
 
Ariel Ortiz
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I'd have to go poke around in the specs...have you done that? What have you found?


Hi Bert. I appreciate your response.

I tried to look for an answer directly from the MIDP 2.0 API javadocs, but unfortunately I've found nothing so far.

I�ve been searching other Web pages and some authors talk about opaque and transparent pixels, thus I think my original assumption is correct.
[ December 16, 2005: Message edited by: Ariel Ortiz ]
 
Sathya Srinivasan
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My understanding is that the term 'opaque pixel' refers to a pixel having an alpha value of (2 ^ Display.numAlphaLevels() - 1).

So, it is considered a collision if two pixels having an alpha value of 'opaque' to ensure that collision among transparent pixels are not taken into account.

Since an image may be non-rectangular, there will be some transparent pixels around the image (like around the head) to cover the rest of the bounding rectangle. In a game-like application, you want to ensure that a collision occurs only when the image (say, the head) hits something and not the bounding rectangle.

Look at the Alpha Processing section of the Image class for more example.

http://www.j2medev.com/api/midp/javax/microedition/lcdui/Image.html
 
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