Pixel aligning lines using Quartz (from the TreeView sample code)

quartzPixelAlign

    // Compute the needed adjustment in x and y to align our lines for crisp, exact pixel coverage.  (We can only do this if the lineWidth is integral, which it usually is.)
    CGFloat adjustment = 0.0;
    CGFloat lineWidth = [[self enclosingTreeView] connectingLineWidth];
    NSSize lineSize = NSMakeSize(lineWidth, lineWidth);
    NSSize lineSizeInPixels = [self convertSizeToBase:lineSize];
    CGFloat halfLineWidthInPixels = 0.5 * lineSizeInPixels.width;
    if (fabs(halfLineWidthInPixels - floor(halfLineWidthInPixels)) > 0.0001) {
        // If line width in pixels is odd, lay our path segments along the centers of pixel rows.
        NSSize adjustmentAsSizeInPixels = NSMakeSize(0.5, 0.5);
        NSSize adjustmentAsSize = [self convertSizeFromBase:adjustmentAsSizeInPixels];
        adjustment = adjustmentAsSize.width;
    }

    NSRect bounds = [self bounds];
    NSPoint basePoint;

    // Compute point at right edge of root node, from which its connecting line to the vertical line will emerge.
    NSPoint rootPoint = NSMakePoint(NSMinX(bounds), NSMidY(bounds));

    // Align the line to get exact pixel coverage, for sharper rendering.
    basePoint = [self convertPointToBase:rootPoint];
    basePoint.x = round(basePoint.x) + adjustment;
    basePoint.y = round(basePoint.y) + adjustment;
    rootPoint = [self convertPointFromBase:basePoint];

    // Compute point (really, we're just interested in the x value) at which line from root node intersects the vertical connecting line.
    NSPoint rootIntersection = NSMakePoint(NSMidX(bounds), NSMidY(bounds));

    // Align the line to get exact pixel coverage, for sharper rendering.
    basePoint = [self convertPointToBase:rootIntersection];
    basePoint.x = round(basePoint.x) + adjustment;
    basePoint.y = round(basePoint.y) + adjustment;
    rootIntersection = [self convertPointFromBase:basePoint];