R – speed up the use of Core Graphics to draw moving triangles every 1/10th of a second

I have recently added some Core Graphics elements to my app and it has slowed dramatically, rendering it just about useless. I am not sure if I am just not using Core Graphics efficiently (how do I make it faster?) or if this problem is inherent in the use of Core Graphics. My code is below, after this description:

There are speech bubbles that move around the screen (in x & y). Each bubble has a corresponding image at the bottom of the screen that also moves in x & y. I am using Core Graphics to draw a triangle from the speech bubbles, terminating at the bottom images. There can be more than 10 of these triangles on the screen at once, all moving. Every 1/10th of a second a timer fires, calculates the positions of everything, and calls setNeedsDisplayon the triangle object I have built.

Code for the triangle object:

- (void)drawRect:(CGRect)rect {
    // Drawing code
 // Drawing code
 CGContextRef ctx = UIGraphicsGetCurrentContext(); //get the graphics context
 CGContextSetRGBStrokeColor(ctx, 1.0, 0, 0, 1); //there are two relevant color states, "Stroke" -- used in Stroke drawing functions and "Fill" - used in fill drawing functions

 //Create an array of points for triangle  
 CGPoint leftTrianglePoint;
 CGPoint rightTrianglePoint;
 rightTrianglePoint = CGPointMake(pointBlob.x, (pointBlob.y + 10.0));
 leftTrianglePoint = CGPointMake(pointBlob.x, (pointBlob.y - 10.0));

 CGPoint triangleArray [] =
 {
  pointGrid,
  rightTrianglePoint,
  leftTrianglePoint,
 pointGrid,};

 //Add lines to the context
 CGContextAddLines( ctx, triangleArray, 4);
 //draw the path

 //color the context - using a function for gray, to matche the saved blobs
 CGContextSetGrayFillColor(ctx, 0.0, .7);

 //Now fill the path 
 CGContextFillPath(ctx);
}

How can I speed this up / build efficiency so my graphics move smoothly again?