Subject:
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Re: Rendering implementation details
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Newsgroups:
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lugnet.cad.dev
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Date:
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Mon, 24 Jan 2005 22:13:07 GMT
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Viewed:
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1973 times
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In lugnet.cad.dev, Mark Tarrabain wrote:
> I was envisioning how an LDraw renderer would be implemented if it were
> done with OpenGL, and I've arrived at some questions that I can't answer
> for myself.
>
> I'm particularly wondering about line type #5, the optional line.
> According to the LDraw file format specification: "This draws a line
> between the first two points, if the projections of the last two points
> onto the screen are on the same side of an imaginary line through the
> projections of the first two points onto the screen." I understand
> what this means, but I'm confused about certain details of
> implementation that could, as near as I can see, be the cause of some
> inefficiency.
>
> For this line type, using OpenGL one thing I came up with was that one
> would use gluProject on each vertex on both line segments to see where
> they would fall on screen, examine the end points, and then decide
> whether or not to draw them based on that, but I would imagine calling
> gluProject 4 times for each optional line listed in a part definition
> (especially since not all of them are necessarily even displayed!) would
> adversely affect performance. The only other way I could see it
> working is to do _all_ the rendering in the application, and not rely on
> something like opengl at all. Again, I would imagine this to severely
> impact performance.
>
> Could anyone enlighten me as to how this could be done without making
> serious compromises in efficiency? Or am I completely out to lunch
> about the performance impact of the concerns I've mentioned?
>
> Thanks in advance.
Someone once suggested to me (Dan from Microsoft maybe?) that given today
graphics libraries, one could probably get away with ignoring op-lines
altogether and use edge detection. This would present a potential problem since
edge color is dependant on part color.
-Orion
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Message is in Reply To:
 | | Rendering implementation details
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| I was envisioning how an LDraw renderer would be implemented if it were done with OpenGL, and I've arrived at some questions that I can't answer for myself. I'm particularly wondering about line type #5, the optional line. According to the LDraw (...) (20 years ago, 24-Jan-05, to lugnet.cad.dev)
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