Corners of a sprite, without matrices
Blitz3D Forums/Blitz3D Programming/Corners of a sprite, without matrices
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| Let's say we have a quad we want to face the camera. Given the position of the camera, and the position of the quad, we can calculate a vector we want to align the quad to. The quad is defined as four vertices at (-1,-1,0),(-1,1,0),(1,1,0), and (1,-1,0). Now, what is the fastest way to calculate the new coordinates, hopefully without using matrices? |
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| Take your normal which points in the direction your object faces. We'll call this NormalX. This is the hard part: Calculate normals which are 90 degrees to this normal. Call these NoralY and NormalZ. This is hard because you may have a normal which points towards the camera, but you have no defined up/down left/right. You'll have to decide how you're going to determine those directions for yourself. Once you've done that, all you need do is this: Multiply NormalX by the new point's X coordinate. Multiply NormalY by the new point's Y coordinate. Multiply NormalZ by the new point's Z coordinate. Add the three normals. The result is the location of your transformed point. You can imagine this like moving a knight on a rotated chessboard. First you move it along the transformed X axis, then along the transformed Y axis, and finally you move it along the transformed Z axis because I just took it with that pawn you failed to notice. |
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