Basic collision direction detection on 2d objects
- by Osso Buko
I am trying to develop a platform game for Android by using ANdroid GL Engine (ANGLE). And I am having trouble with collision detection. I have two objects which is shaped as rectangular. And no change in rotation. Here is a scheme of attributes of objects.
What i am trying to do is when objects collide they block each other's movement on that direction. Every object has 4 boolean (bTop, bBottom, bRight, bLeft). For example when bBottom is true object can't advance on that direction.
I came up with a solution but it seems it only works on one dimensional. Bottom and top or right and left.
public void collisionPlatform (MyObject a, MyObject b) {
// first obj is player and second is a wall or a platform
Vector p1 = a.mPosition; // p1 = middle point of first object
Vector d1 = a.mPosition2; // width(mX) and height of first object
Vector mSpeed1 = a.mSpeed; // speed vector of first object
Vector p2 = b.mPosition; // p1 = middle point of second object
Vector d2 = b.mPosition2; // width(mX) and height of second object
Vector mSpeed2 = b.mSpeed; // speed vector of second object
float xDist, yDist; // distant between middle of two object
float width , height; // this is average of two objects measurements width=(width1+width2)/2
xDist=(p1.mX - p2.mX); // calculate distance // if positive first object is at the right
yDist=(p1.mY - p2.mY); // if positive first object is below
width = d1.mX + d2.mX; // average measurements calculate
height = d1.mY + d2.mY;
width/=2;
height/=2;
if (Math.abs(xDist) < width && Math.abs(yDist) < height) { // Two object is collided
if(p1.mY>p2.mY) { // first object is below second one
a.bTop = true;
if(a.mSpeed.mY<0) a.mSpeed.mY=0;
b.bBottom = true;
if(b.mSpeed.mY>0) b.mSpeed.mY=0;
} else {
a.bBottom = true;
if(a.mSpeed.mY>0) a.mSpeed.mY=0;
b.bTop = true;
if(b.mSpeed.mY<0) b.mSpeed.mY=0;
}
}
As seen in my code it simply will not work. when object comes from right or left it doesn't work. I tried couple of ways
other than this one but none worked. I am guessing right method will include mSpeed vector. But I have no idea how to do it.
I really appreciate if you could help. Sorry for my bad english.
