"Flatten" or "Merge" Quartz 2D drawn lines

Question

I'm trying to figure out how you can flatten or merge alot of dynamicly drawn lines in Quartz 2D,

I'm drawing random lines over time on my stage, I add new line coordinates each time to an array and draw the array (with my drawRect and I push a new line in my array with a timer and a setNeedDisplay to acctually redraw all the previous lines plus the new one)

now the PROBLEM: after a while it starts to get slower and slower because the arrays are getting very long, so I though I should merge the coordinates into a flat image or something and clear the arrays to keep it memory healthy, but how do I do this?

This is my current workflow:

• Call timer

  [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(drawdrawdraw) userInfo:nil repeats:YES];

• Refresh the drawRect in my "drawdrawdraw" function

  -(void)drawdrawdraw{ [self setNeedsDisplay]; }

• my drawRect

  -(void)drawRect:(CGRect)rect{
      viewContext = UIGraphicsGetCurrentContext();
  
      int count = [mijnArray_r_x count];
  
      float r_x = (float)(random() % 768);
      [mijnArray_r_x insertObject:[NSNumber numberWithFloat:r_x] atIndex:count];
  
      float r_y = (float)(random() % 1004);
      [mijnArray_r_y insertObject:[NSNumber numberWithFloat:r_y] atIndex:count];
  
      float r_w = (float)(random() % 100);
      [mijnArray_r_w insertObject:[NSNumber numberWithFloat:r_w] atIndex:count];
  
      float r_a = (float)(random() % 100);
      [mijnArray_r_a insertObject:[NSNumber numberWithFloat:r_a] atIndex:count];
  
  
      CGContextSetLineWidth(viewContext, 2.0);
      CGContextSetStrokeColorWithColor(viewContext, [UIColor blackColor].CGColor);
      for (int k = 0; k <= count; k++) {
  
          float temp_x = [[mijnArray_r_x objectAtIndex: k] floatValue];
          float temp_y = [[mijnArray_r_y objectAtIndex: k] floatValue];
          float temp_w = [[mijnArray_r_w objectAtIndex: k] floatValue];
          float temp_a = [[mijnArray_r_a objectAtIndex: k] floatValue];
  
          CGPoint pointpointpoint = CGPointMake(temp_x, temp_y);
          CGPoint pointpointpointpoint = CGPointMake(temp_w, temp_a);
          CGContextMoveToPoint(viewContext, pointpointpoint.x, pointpointpoint.y);
          CGContextAddLineToPoint(viewContext, pointpointpoint.x - pointpointpointpoint.x, pointpointpoint.y + pointpointpointpoint.y);
          CGContextStrokePath(viewContext);
      }
  } }
  

Answer 1

You can draw your lines into a UIImage by using UIGraphicsBeginImageContext(). This way, the time needed to draw will be constant, because in each iteration you're only drawing the cached image as a bitmap and the new lines you add.

- (void)drawRect:(CGRect)rect {
  [self.currentImage drawInRect:[self bounds]];
  UIGraphicsBeginImageContext([self bounds].size);
  CGContextRef cgContext = UIGraphicsGetCurrentContext();
  //Draw your lines into the cgContext here...
  self.currentImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
}

This assumes that you have the property currentImage of type UIImage declared.