2d collision detection teaser

Dboy85

Hey, I'm having trouble understanding a piece of Math I came across and am looking for help. Bare with me as its interpreted through programming.
The three vectors at the start are the position of the player, and each end of a line that is used for a collision. I dont understand the use of the cross product as its 2d nor the assignment of "dr",I understand the math but not its use in these circumstances. Delta is the main source of confusion so any help would be cool.

Cheers

Vector planePt1(landscape.xPos,landscape.yPos);
Vector planePt2(landscape.xPos[i+1],landscape.yPos[i+1]);
Vector player(this->pos.x,this->pos.y);
x1 = planePt1.x - player.x;
y1 = planePt1.y - player.y;
x2 = planePt2.x - player.x;
y2 = planePt2.y - player.y;
dx = x2 - x1;
dy = y2 - y1;
dr = sqrtf(powf(dx, 2) + powf(dy, 2));//length of dxy
D = x1*y2 - x2*y1;//Cross product of x1y1x2y2
delta = powf(radiusOfPlayer*0.9,2)*powf(dr,2) - powf(D,2);

//Collision detected
if (delta >=0 )

conorcan2

Dboy85 wrote: »

dr = sqrtf(powf(dx, 2) + powf(dy, 2));//length of dxy
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Given two points, each denoted by x/y co-ordinates, you can get the length of the line between them with this formula.

Dboy85

conorcan2 wrote: »

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Given two points, each denoted by x/y co-ordinates, you can get the length of the line between them with this formula.

Yeah I understand the Math and formula but the reasoning behind it is the problem.