Cocoa (not touch) collision detection of two circles - objective-c

Question

I am trying to detect the collision of two circles. The process works when a user creates circles (button click) and then mouse clicks on one of the circles to activate it. Mouse clicking anywhere outside the active circle will move the circle to the x,y of the mouse click. What I want to do is stop the movement if there is another circle within the path of the active circle.
NSPoint P = the mouse click (passed in through a notification center)
activeView = the selected circle (subclass of NSView)
My process is to get the point to move to, determine the direction of movement based on the start and end points and also the number of increments for the x start and end points, loop through the increments, use the animator method of NSView to move the view, loop through all non-active views (all the other circles) and compare their position to the current position of the active view using the formula ((x1*x2)+(x1*x2)) + (y1*y2)+(y1*y2) and comparing to the square of the radius of both circles (the circles are in a 30x30 rect with a 4 pixel stroke on the circles, so I used 26 for my radius (26*26) check.
I have a couple of issues (aside from my desire to reinvent the wheel : D - this is a learning exercise for me):
1: The movement code part actually works great. However, I'd like to get the center point of the circle on the mouse click, right now the circle is stopping so that the NSRect that contains it (30x30) x,y coordinate is at the mouse click (this is not flipped, so its lower left).
2: I am getting some collision detection but this seems to be only when the x,y of both containing rects intersect, not the circle edges.
3: Unrelated to all this, I have the NSColor for the containing rects set to clearColor and they initially start out that way but then when I move them they revert back to the default color (that gray color). Do I have to assign the clearColor each time the view is redrawn?
Thanks for the help.
hasCollision = NO;
//get point clicked value
NSValue* pVal = [[notification userInfo] objectForKey:#"dataPoint"];
//convert value to point (end point)
NSPoint p = [pVal pointValue];
//get activeView frame
NSRect avFrame = [activeView frame];
float startX = avFrame.origin.x; //x1
float startY = avFrame.origin.y; //y1
float endX = p.x; //x2
float endY = p.y; //y2
//set direction of activeView movement
if (endX > startX && endY > startY) {
//NSLog(#"endXY > startXY");
cStart = startX;
cCheck =endX;
distanceX = endX - startX;
incrementY = (endY - startY)/distanceX;
} else if (endX < startX && endY > startY) {
//NSLog(#"endX<startX, endY>startY");
cStart = endX;
cCheck =startX;
distanceX = startX - endX;
incrementY = (endY - startY)/distanceX;
} else if (endX < startX && endY < startY) {
//NSLog(#"endX<startX, endY<startY");
cStart = endX;
cCheck =startX;
distanceX = startX - endX;
incrementY = (startY - endY)/distanceX;
} else {
//NSLog(#"endX>startX, endY<startY");
cStart = startX;
cCheck =endX;
distanceX = endX - startX;
incrementY = (startY - endY)/distanceX;
}
//NSLog(#"Start:%f:%f:End%f:%f:::distance=%f:::Y Increment=%f", startX, startY, endX, endY, distanceX, incrementY);
float currentX = startX;
float currentY = startY;
for(int c=cStart; c<cCheck; c++) {
//get move coordinates
if (endX > startX && endY > startY) {
currentX++;
currentY = currentY + incrementY;
} else if (endX < startX && endY > startY) {
currentX--;
currentY = currentY + incrementY;
} else if (endX < startX && endY < startY) {
currentX--;
currentY = currentY - incrementY;
} else {
currentX++;
currentY = currentY - incrementY;
}
//move view
[[activeView animator] setFrame:NSMakeRect(currentX, currentY, avFrame.size.width, avFrame.size.height)];
//make a rect for each object
NSRect avRect = [activeView frame];
//store previous positions
prevPos = [activeView frame];
//check for collisions
for(int v=0; v<[createdViewsDict count]; v++) {
//get the id of the view in the dict
NSString* nextNum = [NSString stringWithFormat:#"circle_%i", v+1];
//init a view and assign it to the next view in the dict
NSView* thisView = [createdViewsDict objectForKey:nextNum];
//make sure this view is not our active view
if (thisView != activeView) {
NSRect tvRect = [thisView frame];
//get the xy coordinates to compare
float x1 = avRect.origin.x;
float y1 = avRect.origin.y;
float x2 = tvRect.origin.x;
float y2 = tvRect.origin.y;
float radius = 26.0;
float dx = x2-x1;
float dy = y2-y1;
float radii = radius + radius;
if ( ( dx * dx ) + ( dy * dy ) < radii * radii ) {
hasCollision = YES;
//[[activeView animator] setFrame:NSMakeRect(prevPos.origin.x, prevPos.origin.y, avFrame.size.width, avFrame.size.height)];
NSLog(#"Collision!!Moving object coords:x=%f,y=%f,:::::::::Stationary object coords:x=%f,y=%f", avRect.origin.x, avRect.origin.y, tvRect.origin.x, tvRect.origin.y);
}
/*
//check for collision
NSRect collisionRect = NSIntersectionRect(avRect, tvRect);
//move circle to previous
if ( !NSIsEmptyRect(collisionRect) ) {
hasCollision = YES;
[[activeView animator] setFrame:NSMakeRect(prevPos.origin.x, prevPos.origin.y, avFrame.size.width, avFrame.size.height)];
NSLog(#"Collision!!Moving object coords:x=%f,y=%f,:::::::::Stationary object coords:x=%f,y=%f", avRect.origin.x, avRect.origin.y, tvRect.origin.x, tvRect.origin.y);
}
*/
}
}
if(hasCollision == YES) {
[[activeView animator] setFrame:NSMakeRect(prevPos.origin.x - 20.0, prevPos.origin.y - 20.0, avFrame.size.width, avFrame.size.height)];
hasCollision = NO;
break;
}
}