I am working on a 3D packing algorithm (MIT-licensed). The box and the cuboids it contains are displayed as a 2D projection. The order of drawing the cuboids (now represented as polygons) is important: a cuboid placed at the back of the box must not be drawn after the cuboids in the front row. I am currently using order by(cuboid.X + cuboid.Y + cuboid.Z) and it works around 99% of the time, but not always. Some aberrations do ocurr, as depicted below. I have tried multiplying the coordinates, and order by X then by Y then by z, and other combinations. Adding the coordinates is the one that gave the best result. POV-ordering has been suggested, but it won't work, as illustrated by the second diagram. Can someone enlighten me?
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$\begingroup$ I assume that using a depth buffer is off the table, right? $\endgroup$– Nicol BolasCommented Feb 10, 2022 at 17:29
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1 Answer
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Let's get our orientation straight first. When I speak of a direction, I mean the direction relative to our viewpoint. So the "front" face of a cuboid is the face nearest the camera; "back" means the face pointing away from the camera. The "left" face of a cuboid is the face pointing to the left from the camera's view.
A cuboid X is in front of cuboid Y if one of the following is true:
- The back face of X is in front of the front face of Y
- The left face of X is to the right of the right face of Y.
If either of these is true, then Y should be drawn before X. This is how you build your sort order. If one of the above is true, then Y should be "less than" X and thus come earlier in the sort.
Note that this algorithm assumes exact math is used to compute the faces of the cuboids for comparison purposes. If you're using floating-point math, you may encounter precision issues that cause problems.
