Need Help With Determinig A Formula

[I_Mystic_I]

What formula could i use if i wanted to determine if a single point landed inside a set of points (i.e., triangle or circle)?

[MarauderIIC]

Use the vertices (corners) of what you're checking.

Square's easy.

Code: Select all

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The point's x coordinate is greater than the left hand side's vertices x-coordinates and less than the right hand side's vertices x-coordinates (which are equal so you only have to use the left and right hand sides', not all four) and similarly it's between the y-coordinates of the top and bottom vertices (which are equal so you only have to use one from the top and one from the bottom too)

For a triangle, it'd be a bit more complicated... you'd have to check what the bounds are at that particular point, I think. Not really sure...

Circle, check that the distance between the point and the center of the circle is less than the radius of the circle. (x2-x1 + y2-y1 < r, I think).

[avansc]

What formula could i use if i wanted to determine if a single point landed inside a set of points (i.e., triangle or circle)?

EDIT: this code works for any geometry. skew lines and so on.

just some code from my old stuff, good code.

let me know if you need help implimenting it.

Code: Select all

bool SimCol::pointInSphere(float sX, float sY, float sR, float x, float y)
{
	float dist = (sX - x)*(sX - x) + (sY - y)*(sY - y);
	if(dist < sR*sR)
		return true;
	return false;
}

bool SimCol::lineInter(line &AB, line &CD)
{
	if(((CD.y2 - CD.y1)*(AB.x2 - AB.x1) - (CD.x2 - CD.x1)*(AB.y2 - AB.y1)) == 0)
		return false;

	if(((CD.y2 - CD.y1)*(AB.x2 - AB.x1) - (CD.x2 - CD.x1)*(AB.y2 - AB.y1)) != 0)
	{
		if(((((CD.x2 - CD.x1)*(AB.y1 - CD.y1) - (CD.y2 - CD.y1)*(AB.x1 - CD.x1))/
				((CD.y2 - CD.y1)*(AB.x2 - AB.x1) - (CD.x2 - CD.x1)*(AB.y2 - AB.y1))) > 0) && ((((CD.x2 - CD.x1)*(AB.y1 - CD.y1) - (CD.y2 - CD.y1)*(AB.x1 - CD.x1))/
				((CD.y2 - CD.y1)*(AB.x2 - AB.x1) - (CD.x2 - CD.x1)*(AB.y2 - AB.y1))) < 1))
		{
			if((((AB.x2 - AB.x1)*(AB.y1 - CD.y1) - (AB.y2 - AB.y1)*(AB.x1 - CD.x1))/
				((CD.y2 - CD.y1)*(AB.x2 - AB.x1) - (CD.x2 - CD.x1)*(AB.y2 - AB.y1)) > 0) && (((AB.x2 - AB.x1)*(AB.y1 - CD.y1) - (AB.y2 - AB.y1)*(AB.x1 - CD.x1))/
				((CD.y2 - CD.y1)*(AB.x2 - AB.x1) - (CD.x2 - CD.x1)*(AB.y2 - AB.y1)) < 1))
			{
				return true;
			}
		}
	}

	return false;
}

bool SimCol::lineInSphere(float sX, float sY, float sR, line &AB)
{
	if(this->pointInSphere(sX, sY, sR, AB.x1, AB.y1))
		return true;
	if(this->pointInSphere(sX, sY, sR, AB.x2, AB.y2))
		return true;

	float dx = AB.x2 - AB.x1;
	float dy = AB.y2 - AB.y1;
	float d = dx*dx + dy*dy;
	float D = (AB.x1 - sX)*(AB.y2 - sY) - (AB.x2 - sX)*(AB.y1 - sY);
	float delta = ((sR*sR) * d) - (D*D);

	float sgn = 0;
	float dyP = dy;

	if(dyP<0)
		dyP = -1 *dyP;

	if(dy < 0)
	{
		sgn = -1;
	}else{
		sgn = 1;
	}

	if(((sR*sR) * (((AB.x2 - AB.x1)*(AB.x2 - AB.x1)) + ((AB.y2 - AB.y1)*(AB.y2 - AB.y1)))) - (((AB.x1 - sX)*(AB.y2 - sY) - (AB.x2 - sX)*(AB.y1 - sY))*((AB.x1 - sX)*(AB.y2 - sY) - (AB.x2 - sX)*(AB.y1 - sY))) >= 1)
	{
		if(((D*dy + sgn * dx * sqrt(sR*sR*d - D*D)) / d) >= AB.x1 && ((D*dy + sgn * dx * sqrt(sR*sR*d - D*D)) / d) <= AB.x2)
			return true;
		if(((D*dy + sgn * dx * sqrt(sR*sR*d - D*D)) / d) >= AB.x2 && ((D*dy + sgn * dx * sqrt(sR*sR*d - D*D)) / d) <= AB.x1)
			return true;
	}

	return false;
}

[Falco Girgis]

Wow, avansc, those are some extremely useful functions. We should make a thread of random useful functions like that.

[I_Mystic_I]

thnx for all the help i think i found what im going to use...