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### #ActualBrother Bob

Posted 17 May 2013 - 06:03 AM

Yes, I assume that as well. But a difference in projection does not have to mean a difference in coordinates. With proper setup, he can indeed draw the same things and get the same result and that was the point of your and my reply. They are fundamentally different types of projection because you cannot blindly replace one with the other. The w and d in your code has to be calculated. That's fine, and the calculations is going to involve, in one way or another, the expressions I gave: w and d are going to depend on the FOV and the Z, and will only be valid for that particular FOV and Z. Your w and d are nothing more that compensation for the differences between orthographic and perspective projection.

He said he wanted 2D with layers, so your w and d, or my xrange and zrange, will necessarily have to be recalculated for each Z. An orthographic projection still allows layering and depth, but there's no need to recalculate anything for different depths, and the coordinate system can be directly and explicitly specified with the desired ranges. That is why I ultimately asked the question if his perspective approach is really necessary, or just based on the no-so-uncommon erroneous belief that your program cannot have multiple types of projections.

### #1Brother Bob

Posted 17 May 2013 - 06:01 AM

Yes, I assume that as well. But a difference in projection does not have to mean a difference in coordinates. With proper setup, he can indeed draw the same things and get the same result and that was the point of your and my reply. They are fundamentally different types of projection because you cannot blindly replace one with the other. You just said yourself that you had to calculate the w and d in your code. That's fine, and the calculations is going to involve, in one way or another, the expressions I gave: w and d are going to depend on the FOV and the Z, and will only be valid for that particular FOV and Z. Your w and d are nothing more that compensation for the differences between orthographic and perspective projection.

He said he wanted 2D with layers, so your w and d, or my xrange and zrange, will necessarily have to be recalculated for each Z. An orthographic projection still allows layering and depth, but there's no need to recalculate anything for different depths, and the coordinate system can be directly and explicitly specified with the desired ranges. That is why I ultimately asked the question if his perspective approach is really necessary, or just based on the no-so-uncommon erroneous belief that your program cannot have multiple types of projections.

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