Making a Grid in an NSView

Question

I currently have an NSView that draws a grid pattern (essentially a guide of horizontal and vertical lines) with the idea being that a user can change the spacing of the grid and the color of the grid.

The purpose of the grid is to act as a guideline for the user when lining up objects. Everything works just fine with one exception. When I resize the NSWindow by dragging the resize handle, if my grid spacing is particularly small (say 10 pixels). the drag resize becomes lethargic in nature.

My drawRect code for the grid is as follows:

-(void)drawRect:(NSRect)dirtyRect {

    NSRect thisViewSize = [self bounds];

    // Set the line color

    [[NSColor colorWithDeviceRed:0 
                           green:(255/255.0) 
                            blue:(255/255.0) 
                           alpha:1] set];

    // Draw the vertical lines first

    NSBezierPath * verticalLinePath = [NSBezierPath bezierPath];

    int gridWidth = thisViewSize.size.width;
    int gridHeight = thisViewSize.size.height;

    int i;

    while (i < gridWidth)
    {
        i = i + [self currentSpacing];

        NSPoint startPoint = {i,0};
        NSPoint endPoint = {i, gridHeight};

        [verticalLinePath setLineWidth:1];
        [verticalLinePath moveToPoint:startPoint];
        [verticalLinePath lineToPoint:endPoint];
        [verticalLinePath stroke];
    }

    // Draw the horizontal lines

    NSBezierPath * horizontalLinePath = [NSBezierPath bezierPath];

    i = 0;

    while (i < gridHeight)
    {
        i = i + [self currentSpacing];

        NSPoint startPoint = {0,i};
        NSPoint endPoint = {gridWidth, i};

        [horizontalLinePath setLineWidth:1];
        [horizontalLinePath moveToPoint:startPoint];
        [horizontalLinePath lineToPoint:endPoint];

        [horizontalLinePath stroke];
    }
}

I suspect this is entirely to do with the way that I am drawing the grid and am open to suggestions on how I might better go about it.

I can see where the inefficiency is coming in, drag-resizing the NSWindow is constantly calling the drawRect in this view as it resizes, and the closer the grid, the more calculations per pixel drag of the parent window.

I was thinking of hiding the view on the resize of the window, but it doesn't feel as dynamic. I want the user experience to be very smooth without any perceived delay or flickering.

Does anyone have any ideas on a better or more efficient method to drawing the grid?

All help, as always, very much appreciated.

Answer 1

You should run Instruments Cpu Sampler to determine where most of the time is being spent and then optimized based on that info. If it's the stroke, put it outside the loop. If it's drawing the path, try offloading the rendering to the gpu. See if CALayer can help.