How to draw a tapered line + oval shadow in Cocoa

Question

Background:

The shot below is of Mail.app in OS X Lion. When the source list gets too long, a nice shadowy line appears just above the buttons at th

Answer 1

General Idea:

.

1. Create a layer "Layer A" with dimensions 150px × 10px
   and fill it with a Gradient with:
   • lower color: #535e71 opacity: 33%
   • upper color: #535e71 opacity: 0%
2. Create a layer "Layer B" with dimensions 150px × 1px
   and fill it with solid #535e71 opacity: 50%
3. Compose "Layer A" and "Layer B" together into "Layer C".
4. Apply reflected gradient mask from #ffffff to #000000 to "Layer C".

Visual Steps:

Functional Code:

MyView.h:

#import 

@interface MyView : NSView {
@private

}

@end

MyView.m:

#import "MyView.h"

@implementation MyView

- (CGImageRef)maskForRect:(NSRect)dirtyRect {
    NSSize size = [self bounds].size;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, size.width, size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);

    CGContextClipToRect(context, *(CGRect*)&dirtyRect);

    CGRect rect = CGRectMake(0.0, 0.0, size.width, size.height);

    size_t num_locations = 3;
    CGFloat locations[3] = { 0.0, 0.5, 1.0 };
    CGFloat components[12] = {
        1.0, 1.0, 1.0, 1.0,  // Start color
        0.0, 0.0, 0.0, 1.0,  // Middle color
        1.0, 1.0, 1.0, 1.0,  // End color
    };

    CGGradientRef myGradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, num_locations);

    CGPoint myStartPoint = CGPointMake(CGRectGetMinX(rect), CGRectGetMinY(rect));
    CGPoint myEndPoint = CGPointMake(CGRectGetMaxX(rect), CGRectGetMinY(rect));

    CGContextDrawLinearGradient(context, myGradient, myStartPoint, myEndPoint, 0);

    CGImageRef theImage = CGBitmapContextCreateImage(context);
    CGImageRef theMask = CGImageMaskCreate(CGImageGetWidth(theImage), CGImageGetHeight(theImage), CGImageGetBitsPerComponent(theImage), CGImageGetBitsPerPixel(theImage), CGImageGetBytesPerRow(theImage), CGImageGetDataProvider(theImage), NULL, YES);

    [(id)theMask autorelease];

    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);

    return theMask;
}

- (void)drawRect:(NSRect)dirtyRect {
    NSRect nsRect = [self bounds];
    CGRect rect = *(CGRect*)&nsRect;
    CGRect lineRect = CGRectMake(rect.origin.x, rect.origin.y, rect.size.width, (CGFloat)1.0);

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGContextRef context = (CGContextRef) [[NSGraphicsContext currentContext] graphicsPort];
    CGContextClipToRect(context, *(CGRect*)&dirtyRect);
    CGContextClipToMask(context, rect, [self maskForRect:dirtyRect]);

    size_t num_locations = 2;
    CGFloat locations[2] = { 0.0, 1.0 };
    CGFloat components[8] = {
        0.315, 0.371, 0.450, 0.3,  // Bottom color
        0.315, 0.371, 0.450, 0.0  // Top color
    };

    CGGradientRef myGradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, num_locations);

    CGPoint myStartPoint = CGPointMake(CGRectGetMinX(rect), CGRectGetMinY(rect));
    CGPoint myEndPoint = CGPointMake(CGRectGetMinX(rect), CGRectGetMaxY(rect));

    CGContextDrawLinearGradient(context, myGradient, myStartPoint, myEndPoint, 0);

    CGContextSetRGBFillColor(context, 0.315, 0.371, 0.450, 0.5 );
    CGContextFillRect(context, lineRect);

    CGColorSpaceRelease(colorSpace);    
}

@end

(My first time using pure low-level CoreGraphics, thus possibly sub-par optimal, open for improvements.)

This is an actual screenshot of what the code above produces:

The drawing stretches to the view's dimensions.

_{(I formerly had two techniques shown here: "Technique A" & "Technique B".
"Technique B" provided superior results and was way simpler to implement as well, so I ditched "Technique A".
Some comments may still refer to "Technique A" though. Just ignore them and enjoy the fully functional code snippet.).}