How can I render line faster than CGContextStrokePath?

Question

I\'m plotting ~768 points for a graph using CGContextStrokePath. The problem is that every second I get a new data point, and thus redraw the graph. This is currently taking 5

Answer 1

Create a bitmap context the same height as your view but twice the width. Start drawing your points into the context, then in drawRect create a CGImageRef. The idea is to as you initially fill the screen your image will start at the beginning. The image you will draw will have the proper width and height, but the bytesPerRow will be 2x (more on that). You continue to draw new points as they come until you get to the last point - now x is exhausted.

Continue writing points in your context, but now, when you create the image, offset the initial pointer by one pixel. Continue doing this until you have done 2x lines - you are now at the very very end of your context.

At that one time, you will need to move the "right" side of the image to the left, and reset your offset count. That is, you will need to memcpy(starOfBitMap, startOfBitMap+bytesPerRow/2, sizeOfBitMap - bytesPerRow/2). In essence, you are left shifting one visible frame.

Now as you add new lines, its at the end of the first frame, and you start offseting by one pixel as you draw.