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SAT / Separating Axis Theorem math: y no werk

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ponut64:
I have made 2 versions (well... I broke one as it is saved too late past the conversion process to the other) of some 3D collison/zone detection math using RBB [rotated bounding box] based on the separating axis theorem.

One version uses entirely FIXED data types. It generates non-zero numbers, but there are overflows due to numbers being squared (600 squared, for instance, is beyond the range of FIXED data).

One version (that can compile) I made to combat the overflows is programmed using jo_vectorf and Sint32 values and should make the final conclusion more likely/less buggy (removal of decimal points in end comparison). But there is a problem... all the numbers are zero, and I don't know why. All of the math up to slInnerProduct (replaced with jo_vectorf_dot) and JO_SQUARE (being the overflow area) worked previously, now it doesn't work at all. At some point I had that same math working with jo_vectorf and Sint32 data, but jo_vectorf_dot would not operate since this was a situation in which the vectors were not stored as pointers (and instead "stack variables" or you know, missing the * in jo_vectorf *vector_here_is_pointer_with_star ).

And the other factoid, if I remove the initialization from jo_vectorf structs, it crashes.

Here is the jo_vectorf (float/int) code that I am trying to use:
http://www.mediafire.com/file/q9xmx8cd06c2666/bounder.c

Here, for comparison, is the (broken) more-SGL-reliant code:
http://www.mediafire.com/file/kwbr3kb5xa01u3c/bounder_broke.c

Thank you for reading.
The answer is probably simple. Maybe I am trying to typecast something wrong or am using jo_float2fixed and/or toFIXED improperly.

and here's the entire project
http://www.mediafire.com/file/nypbx88obigj3x7/RTFK.zip


/e: thread has a conclusion
http://www.mediafire.com/file/do4493rxrmyqk59/bounder_share.c

XL2:
SGL is using tables AFAIK for the square root functions , so the cost shouldn't be higher than doing a sin/cos.
Jo Engine also has some tricks to reduce cpu usage.
I don't have time this week to look at your code, but maybe you can try that.

XL2:
I just took a short look at your code, and I need to ask : are you trying to build a space rocket?
Just kidding, but seriously you are overcomplicating this.

You can just use a bounding sphere around your objects or an AABB (like for the whole mesh so it's fast).
If you want a per quad collision detection, start with the AABB/sphere detection, then find a point on each quad (a vertices) and use the quad's normal to do an innerproduct (using your position minus the verticle position).
If the result is <= 0, you can check if you are crossing this quad (AABB again should be good enough, just find the minimum and maximum points) and check if you were crossing the quad's plane before updating your position.
It should take around 30 lines of code max and should be way faster than what you are doing.

ponut64:
I am focused on using an arbitrary RBB (rotated bounding box). Not related to the mesh, just calculated. That's in the code, it works just the values are not being changed, but I did not know how to test a point against any 8 points making a rectangle that is rotated in any way.

I don't see how an amalgamation of AABB can achieve precisely what an RBB does.

I know what I am doing is very complicated, probably way more complicated than it needs to be, but I was hoping that I could at least get a non-zero result out of jo_vectorf structs.
Per-quad collision detection is not desired, as that should be in theory more complicated than what I want to do assuming I understood how to simplify what I want to do.

I can't fathom a way to compare a point against 8 other points that make segments that are not axis-aligned... the way I figured that could be done was project all the points on the X, Y, and Z axis vectors of the box, these projections make axis-aligned segments to that particular box (that is rotated), and if the point compared against the box overlaps with the segments then it collides (found by comparing the segments of "player" to "segment max" plus "player" to "segment min" is equal to "segment max" to "segment min".
Obviously the computationally intensive act of projecting what would end up being 16 points to 6 other vectors would be something that would be triggered by an AABB "physics proximity box" to make it faster.

I am not trying to compare if the "player" collides with the "ring". The core idea is if I can compare if the "player" or any given object is in any other given rotated rectangle area.. I'm sure you know that, but I don't see how an amalgamation of AABB can achieve that precisely.

So yes, I am trying to build a space rocket. Working comes first, simplification later. The core issue is why can I not change the value of a jo_vectorf struct. I do not specifically need these structs, as I could just make another function for inner product that does not need said struct, but I'd like to figure out why. and like i said, its probably something more basic about C programming than anything, as I am a newbie.

thanks for reading & replying

XL2:
I never played with the jo_vectorf, so I couldn't say.
AABB is one cheap way to do general tests, but you can easily do sphere vs sphere tests too.

So to test against rings, you could do something like : test against sphere, which gives you a pretty good idea. Then you test the distance to see if you are crossing the ring's plane  (2x dot products : before updating the player position and after, if signs are different, you crossed the plane). You would just need to calculate the normal vectors, but that's easy : just do a cross product and a distance division to find the normals, which you should do offline or as you load the map.
At the cost of max 2 dot products and sphere calculation, you would get a quite accurate collision detection.
Per quad is easy too, you just need a proper map subdivision (grid, quadtree, octree, kd tree or bsp tree).

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