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### #ActualFinalspace

Posted 10 March 2013 - 12:41 PM

Hi everybody,

i have implemented discrete SAT (Separating Axis Theorem) in the past successfully.

Therefore i have now remade this to fix the "fast moving issue" - calculate the time when the collision first happens - to get a value for scaling the velocity to remove the penetration in the first place.

What i basically do is to test two OBB with two fixed axis of (1, 0) and (0, 1) with the following algorythm:

- Get the relative position (distance) between the 2 OBBs (pA - pA)

- Get the relative velocity between the 2 OBBs (vA - Vb) - Just to remove the second velocity to make the second one static.

- For loop over the two axes

- Project the relative position onto the axis to get an offset based on current axis

- Project A onto current axes and get min/max projection

- Add the offset to projection of A

- Project B onto current axes and get min/max projection

- Calculate distances between min/max projections of A and B (d0, d1)

- Calculate time enter and time leave factor by divide both distances by projected velocity on axis

- Swap time enter with time leave if required (Time enter must always be smaller than time leave)

- Get the highest overlap to skip out collisions which not happens or are too late

- Time Enter is the factor used to fix the velocity.

These steps are implemented a simple JSFiddle demo i have written to visualize the entire process, see here:

http://jsfiddle.net/dku72/

Now what the problem is: There are something missing on it, because the visualized velocity/corrected projection is wrong in some cases (Inverted for Y Axis) and i havent found a solution yet to find the correct single time enter/leave factor. What i want in the end is a "Time of impact" value which can be used to fix the velocity, to project the box on the other box without penetration.

It would be really great if you can help me to fix these problems.

Thanks,

Final

### #1Finalspace

Posted 10 March 2013 - 12:39 PM

Hi everybody,

i have implemented discrete SAT (Separating Axis Theorem) in the past successfully.

Therefore i have now remade this to fix the "fast moving issue" - calculate the time when the collision first happens - to get a value for scaling the velocity to remove the penetration in the first place.

What i basically do is to test two OBB with two fixed axis of (1, 0) and (0, 1) with the following algorythm:

- Get the relative position (distance) between the 2 OBBs (pA - pA)

- Get the relative velocity between the 2 OBBs (vA - Vb) - Just to remove the second velocity to make the second one static.

- For loop over the two axes

- Project the relative position onto the axis to get an offset based on current axis

- Project A onto current axes and get min/max projection

- Add the offset to projection of A

- Project B onto current axes and get min/max projection

- Calculate distances between min/max projections of A and B (d0, d1)

- Calculate time enter and time leave factor by divide both distances by projected velocity on axis

- Swap time enter with time leave if required (Time enter must always be smaller than time leave)

- Get the highest overlap to skip out collisions which not happens or are too late

- Time Enter is the factor used to fix the velocity.

These steps are implemented a simple JSFiddle demo i have written to visualize the entire process, see here:

http://jsfiddle.net/dku72/

Now what the problem is: There are something missing on it, because the visualized velocity/corrected projection is wrong in some cases (Inverted for Y Axis) and i havent found a solution yet to find the correct single time enter/leave factor. (Use the highest values are wrong)
What i want in the end is a "Time of impact" value which can be used to fix the velocity, to project the box on the other box without penetration.

It would be really great if you can help me to fix these problems.

Thanks,

Final

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