Hello,

I'm currently programming a very simple physic engin but recently i've come to a problem i've put too many hours on.

I'm using the separating axis theorem to detect collision between 2 shape (usually a rotating rectangle and a static polygon).

I am calculating the minimum translation vector to resolve collisions.

Everything seems to be working except for one thing:

If an actor (my rotating rectangle) is touching a slope (the static polygon) by only one pixel, the calculated MTV will be (-1,0) insteed of the expected (-1,-1). For everything else, it's working fine.

For the visuals, here is an image.

I'm handling my physic this way: Horizontal first then vertical. Since this is an horizontal collision i would used the MTV (-1, -1) and move the actor Y position up by 1 pixel. The actor X is untouched at this point.

But since the returned MTV is (-1, 0), i can't move the actor up the slope the very first time he touche it.

Here is some of my code. If the lisibility is not acceptable, i will be glade to answers yours questions.

//////////////////////////////////////////////////////////////////////////
//Try to find if an Axis can disprove collision.
bool CMath::Sat(CPolygon *_a, CPolygon *_b, CVector &_mtv, int &_solid)
{
	float overlap = 1000; //Large value.
	CVector smallest(0,0); //MTV (Minimum translation vector). This is the resolving vector.
	int numberofcollision = 0;
	//For polygon A...
	for (int i = 0; i < _a->n; i++)
	{
		// Get the direction vector
		CVector axis = _a->edges[i].dir; 

		// Get the normal of the vector (90 degrees)
		axis = Perp(axis); 

		// Find the projection of a and b onto axis
		CVector p1 = Project(_a,axis), p2 = Project(_b,axis); 

		// If they do not overlap, then no collision
		float o = 1000;
		if (!Overlap(p1,p2, o)) 
			return false; 
		
		//Update the MTV
		else
		{
			if(o < overlap)
			{
				overlap = o;
				smallest = axis;
			}
		}
	}

	// repeat for b
	for (int i = 0; i < _b->n; i++)
	{ 
		CVector axis = _b->edges[i].dir;
		axis = Perp(axis);
		CVector p1 = Project(_a,axis), p2 = Project(_b,axis);

		float o = 1000;
		if (!Overlap(p1,p2, o)) 
			return false;
		else
		{
			if(o < overlap)
			{
				overlap = o;
				smallest = axis;
			}
		}
	}

	//No Axis can prove the Polygon is not colliding, so it must be colliding.
	//Calculate the MTV;
	_solid = smallest.x == 0 || smallest.y == 0;
	smallest = Normalize(smallest);
	_mtv.x = smallest.x * (overlap +  1); //if we are touching something that is not a slope, always push the actor by 1 pixel.
	_mtv.y = smallest.y * (overlap +  1);
	return true;
}

//////////////////////////////////////////////////////////////////////////
//
bool CMath::Overlap(CVector _p1, CVector _p2, float &_overlap)
{
    if (Contains(_p1,_p2, _overlap) ) return true;

    return false;
}

//////////////////////////////////////////////////////////////////////////
//
bool CMath::Contains(CVector _range1, CVector _range2, float &_overlap)
{
	_overlap = abs(_range1.y - _range2.x);
	return (_range1.y >= _range2.x && _range1.x <= _range2.y);
}

Thank you very much for your time. I will continue searching on my ends and will post the solution if i finds it myself.

Ps. I appologize if my english is bad.

Alright, Thank you. I will try that.