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Re: drawing/masking one image with the alpha value from another
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Re: drawing/masking one image with the alpha value from another


  • Subject: Re: drawing/masking one image with the alpha value from another
  • From: David Duncan <email@hidden>
  • Date: Wed, 23 Sep 2009 09:22:43 -0700

On Sep 23, 2009, at 6:25 AM, Roland King wrote:

One question about Transparency Layers, the docs say that when you start one the global alpha is set to 1, shadows are turned off and blend mode is set normal (actually only the Quartz 2D guide says that the blend mode changes, the actual API docs don't mention it). When the layer is ended it's composited back to the original context, what blending mode is used to do that, I assume the original blend mode at the point the Transparency Layer was started right?


You can think of a transparency layer as creating a bitmap context, drawing to it, then creating an image and drawing it to the original context. Its not quite the same, but as far as final results are concerned, it is similar (more to the point, yes the original blend mode should be used for compositing).
--
David Duncan
Apple DTS Animation and Printing


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References: 
 >drawing/masking one image with the alpha value from another (From: Roland King <email@hidden>)
 >Re: drawing/masking one image with the alpha value from another (From: David Duncan <email@hidden>)
 >Re: drawing/masking one image with the alpha value from another (From: Ken Ferry <email@hidden>)
 >Re: drawing/masking one image with the alpha value from another (From: Roland King <email@hidden>)

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