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When masking a bitmap by reducing the polygons it's displayed on, what is the name of doing this?

I often see this done for physics, sort of, to have an edge around an object for detection etc, but a long while ago remember seeing a similar approach being used with polygons for visual masking, but have completely forgotten what it was called or how to find it.

ADDITIONAL INFO:

In this example, the polygons are used to "mask" some of the image:

http://fancyratstudios.com/2010/02/programming/progresstimer-for-cocos2d/

What's the name of using polygons to do masking in this manner?

Confused
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  • I'd call linked solution morphing or keyframe animation. – Andreas May 01 '16 at 12:39
  • Whilst the animation is similar to key framing of animation, that's not the question I'm asking. I'm asking about the fact that the polygons' missing area is used to mask the texture. What's THAT called? – Confused May 01 '16 at 14:07
  • The generic terms are "clipping" for 2D graphics, "culling" for 3D graphics. https://en.wikipedia.org/wiki/Clipping_%28computer_graphics%29 – Hans Passant May 01 '16 at 15:25
  • @HansPassant NO, this is something else entirely. – Confused May 01 '16 at 20:44

2 Answers2

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According to the definition you gave, the technique you're referring to could be Gouraud shading, whose definition is also reported in the Video-Based Rendering book on page 50:

Hole-filling: for polygons that are not depicted in any image, determine appropriate vertex colors; during rendering, Gouraud shading is used to mask the missing texture information.

abarisone
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  • How on earth did you find this? – Confused May 03 '16 at 08:18
  • Do you mean it is useful for you? I did some book reviews about imaging techniques and remembered something similar. But basically I googled around to find it... – abarisone May 03 '16 at 08:44
  • I'm trying to explain this approach, and was hoping there was an easy way to refer to it. I couldn't find anything that gave it a name. As a subset of Gouraud shading techniques, this is very helpful. Now I can reference it with a name! – Confused May 03 '16 at 09:00
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Not sure what your talking about, but it's either rasterization (projecting polygons to a plane), or "apply a texture" (projecting an image to a set of polygons), or decimation (reducing the amount of polygons)

Regis Portalez
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