Recently I have been using the Polygon class to create asteroids as well as bullets and a spaceship. I am currently trying to create the collision detection for the program however it appears that the collision detection only works around 1/5 of the time (no pattern appears as to why it works).
Here's the code.. Creating the Polygon:
void renderPoly() {
int j;
int s = sides;
double r, angle;
int x, y;
for (j = 0; j < s; j++) {
angle = 2 * Math.PI / s * j;
r = MIN_ROCK_SIZE + (int) (Math.random() * (MAX_ROCK_SIZE - MIN_ROCK_SIZE));
x = (int) (r * Math.cos(angle));
y = (int) (r * -Math.sin(angle));
cOM[0] += x;
cOM[1] += y;
pointData[j][0] = x;
pointData[j][1] = y;
}
cOM[0] /= asteroidShape.npoints;
cOM[1] /= asteroidShape.npoints;
for (int i = 0; i < asteroidShape.npoints; i++) {
pointData[i][0] += cOM[0];
pointData[i][1] += cOM[1];
}
}
rotating and moving the polygon:
void move() {
int x, y, i;
//change rotation
theta += rotVel;
//change x
asteroidData[0] += deltaX;
//change y
asteroidData[1] += deltaY;
for (i = 0; i < asteroidShape.npoints; i++) {
x = (int) (pointData[i][0] * Math.cos(theta) - pointData[i][1] * Math.sin(theta) );
y = (int) (pointData[i][0] * Math.sin(theta) + pointData[i][1] * Math.cos(theta) );
asteroidShape.xpoints[i] = x + asteroidData[0];
asteroidShape.ypoints[i] = y + asteroidData[1];
asteroidShape.invalidate();
}
}
check if touching bullet:
boolean hitBullet(Bullet b) {
this.asteroidShape.invalidate();
for (int i = 0; i < b.bulletShape.npoints; i++)
if (this.asteroidShape.contains(b.bulletShape.xpoints[i], b.bulletShape.ypoints[i]) )
return true;
for (int j = 0; j < this.asteroidShape.npoints; j++)
if (b.bulletShape.contains(this.asteroidShape.xpoints[j], this.asteroidShape.ypoints[j]) )
return true;
return false;
}
(the ship method is the same except the constructor requires a ship object)
as well as the loop that calls it in the 'game' class:
for (int i = 0; i < aArray.length-1; i++) {
if (aArray[i] != null) {
for (int j = 0; j < bArray.length-1; j++) {
if (bArray[j] != null) {
if (aArray[i].hitBullet(bArray[j])) {
aArray[i] = null;
bArray[j] = null;
i = aArray.length-1;
j = bArray.length-1;
}
}
else {
i = aArray.length-1;
j = bArray.length-1;
}
}
}
else {
i = aArray.length-1;
}
}
I have been looking around at alternative solutions such as the Separating Axis Theorem however I do have convex polygons at times and since this method (.contains()) already exists I would like to use it.
Any help would be appreciated, thanks!
The easy way to solve this that I've found is to convert Shapes
(in your case Polygon(2D?)) into Areas . You can use Area.intersect(Area) to see if two Areas have collided
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