# Collision SAT - testing an axis

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okay for the life of me whenever I get into collision this always hits me in the face,
I've tried to understand, I've read masses of papers, hints and explanations, but never found a clear implementation.

To my understanding of separating axis theorem, you find axes running along the edge of each object.
You test against each axis until its confirmed the objects are not touching, if you can not confirm the objects are not touching after testing every axis then the objects must be touching.

The bit which gets me is how do I test against an axis, I've not been able to find much elaboration on this.
Does anyone have a basic example or a link to a well commented implementation?

Any and all help appreciated,
Bombshell

EDIT: Sorry, I accidentally posted this in graphics programming, only just noticed -.-''
EDIT: if possible could someone lock or remove this thread, its fairly pointless in the wrong topic, I've made an appropriate updated thread in the Game Programming forum.

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The "axes" are actually perpendicular to the sides of the objects. You then project the objects onto the subspace defined by that axis (by calculating dot products). If they don't intersect in the subspace then they can't intersect in the original space either.

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Okay I've given it a shot, a shot in the dark I've no clue if I'm doing it right or if I'm being a moron.

This is a collision test for a simple "is touching" or "isn't touching" response inside of an AABB, testing against a triangle in Java.
public boolean isColliding(Triangle i) { double axisX, axisY, temp, minB, minT, maxB, maxT; axisX = -(i.y1 - i.y2); axisY = i.x1 - i.x2; //get axis temp = Math.sqrt((axisX * axisX) + (axisY * axisY)); //length of "axis" axisX /= temp; axisY /= temp; //normalize axis //Box temp = (axisX * x) + (axisY * y); //Dot product of top-left minB = maxB = temp; temp = (axisX * x) + (axisY * (y + h)); //bottom-left if (temp > maxB) { maxB = temp; } else if (temp < minB) { minB = temp; } temp = (axisX * (x + w)) + (axisY * (y + h)); //bottom-right if (temp > maxB) { maxB = temp; } else if (temp < minB) { minB = temp; } temp = (axisX * (x + w)) + (axisY * y); //top-right if (temp > maxB) { maxB = temp; } else if (temp < minB) { minB = temp; } //Triangle temp = (axisX * i.x1) + (axisY * i.y1); //Dot product of vert 1 minT = maxT = temp; temp = (axisX * i.x2) + (axisY * i.y2); //vert 2 if (temp > maxT) { maxT = temp; } else if (temp < minT) { minT = temp; } temp = (axisX * i.x3) + (axisY * i.y3); //vert 3 if (temp > maxT) { maxT = temp; } else if (temp < minT) { minT = temp; } if (maxB < minT || minB > maxT) { return false; } // Test other axes // return true; }

is this right?
I'd have created a vector2 class but I despise using functions for addition and subtraction and etc. sadly java has no operator overloading to my knowledge. So everything is fairly raw.

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