Use lighter scrollbar scolor when background is dark.

Headers/iTerm/PTYScrollView.h

@@ -33,6 +33,9 @@
 {
     BOOL userScroll;
 }
+
+@property (nonatomic, assign) BOOL hasDarkBackground;
+
 + (BOOL)isCompatibleWithOverlayScrollers;
 - (id)init;
 - (void) mouseDown: (NSEvent *)theEvent;

Headers/iTerm/PTYTextView.h

@@ -559,5 +559,6 @@ typedef enum {
 // Returns true if any onscreen char is blinking.
 - (BOOL)_markChangedSelectionAndBlinkDirty:(BOOL)redrawBlink width:(int)width;
+- (double)_perceivedBrightness:(NSColor*)c;
 @end

NSBitmapImageRep+CoreImage.h

+//  From http://www.cocoadev.com/index.pl?NSImageCategory
+//
+//  NSBitmapImageRep+CoreImage.h
+//  iTerm2
+//
+
+#import <Foundation/Foundation.h>
+#import <Cocoa/Cocoa.h>
+
+@interface NSBitmapImageRep (CoreImage)
+/* Draws the specified image representation using Core Image. */
+- (void)drawAtPoint:(NSPoint)point
+           fromRect:(NSRect)fromRect
+    coreImageFilter:(NSString *)filterName
+          arguments:(NSDictionary *)arguments;
+@end

NSBitmapImageRep+CoreImage.m

+//  From http://www.cocoadev.com/index.pl?NSImageCategory
+//  NSBitmapImageRep+CoreImage.m
+//  iTerm2
+
+#import <QuartzCore/QuartzCore.h>
+#import "NSBitmapImageRep+CoreImage.h"
+#import "NSImage+CoreImage.h"
+
+#define CIIMAGE_PADDING 16.0f
+
+@implementation NSBitmapImageRep (CoreImage)
+
+- (void)drawAtPoint: (NSPoint)point fromRect: (NSRect)fromRect coreImageFilter: (NSString *)filterName arguments: (NSDictionary *)arguments {
+    NSAutoreleasePool *pool;
+    CIFilter *filter;
+    CIImage *before;
+    CIImage *after;
+    CIContext *ciContext;
+    CGContextRef cgContext;
+
+    pool = [[NSAutoreleasePool alloc] init];
+    before = nil;
+
+    @try {
+        before = [[CIImage alloc] initWithBitmapImageRep: self];
+        if (before) {
+            filter = [CIFilter filterWithName: filterName];
+            [filter setDefaults];
+            if (arguments)
+                [filter setValuesForKeysWithDictionary: arguments];
+            [filter setValue: before forKey: @"inputImage"];
+        } else {
+            filter = nil;
+        }
+
+        after = [filter valueForKey: @"outputImage"];
+        if (after) {
+            if (![[arguments objectForKey: @"gt_noRenderPadding"] boolValue]) {
+                /* Add a wide berth to the bounds -- the padding can be turned
+                 off by passing an NSNumber with a YES value in the argument
+                 "gt_noRenderPadding" in the argument dictionary. */
+                fromRect.origin.x -= CIIMAGE_PADDING;
+                fromRect.origin.y -= CIIMAGE_PADDING;
+                fromRect.size.width += CIIMAGE_PADDING * 2.0f;
+                fromRect.size.height += CIIMAGE_PADDING * 2.0f;
+                point.x -= CIIMAGE_PADDING;
+                point.y -= CIIMAGE_PADDING;
+            }
+
+            cgContext = CGContextRetain((CGContextRef)[[NSGraphicsContext currentContext] graphicsPort]);
+            if (cgContext) {
+                ciContext = [CIContext contextWithCGContext: cgContext options: nil];
+                [ciContext
+                 drawImage:     after
+                 atPoint:       *(CGPoint *)(&point)
+                 fromRect:      *(CGRect *)(&fromRect)];
+                CGContextRelease(cgContext);
+            }
+        }
+    } @catch (NSException *e) {
+        NSLog("exception encountered during core image filtering: %@", e);
+    } @finally {
+        [before release];
+    }
+
+    [pool release];
+}
+@end

NSImage+CoreImage.h

+//  From http://www.cocoadev.com/index.pl?NSImageCategory
+//
+//  NSImage+CoreImage.h
+//  iTerm2
+
+#import <Foundation/Foundation.h>
+#import <Cocoa/Cocoa.h>
+
+@interface NSImage (CoreImage)
+/* Draws the specified image using Core Image. */
+- (void)drawAtPoint: (NSPoint)point fromRect: (NSRect)fromRect coreImageFilter: (NSString *)filterName arguments: (NSDictionary *)arguments;
+
+/* Gets a bitmap representation of the image, or creates one if the image does not have any. */
+- (NSBitmapImageRep *)bitmapImageRepresentation;
+@end
+

NSImage+CoreImage.m

+//  From http://www.cocoadev.com/index.pl?NSImageCategory
+//
+//  NSImage+CoreImage.m
+//  iTerm2
+
+#import "NSImage+CoreImage.h"
+
+@implementation NSImage (CoreImage)
+- (void)drawAtPoint: (NSPoint)point fromRect: (NSRect)fromRect coreImageFilter: (NSString *)filterName arguments: (NSDictionary *)arguments {
+    NSAutoreleasePool *pool;
+    NSBitmapImageRep *rep;
+
+    pool = [[NSAutoreleasePool alloc] init];
+
+    if (filterName) {
+        rep = [self bitmapImageRepresentation];
+        [rep
+         drawAtPoint:       point
+         fromRect:      fromRect
+         coreImageFilter:   filterName
+         arguments:     arguments];
+    } else {
+        /* bypass core image if no filter is specified */
+        [self
+         drawAtPoint:       point
+         fromRect:      fromRect
+         operation:     NSCompositeSourceOver
+         fraction:      1.0f];
+    }
+
+    [pool release];
+}
+
+- (NSBitmapImageRep *)bitmapImageRepresentation {
+    NSImageRep *rep;
+    NSEnumerator *e;
+    Class bitmapImageRep;
+
+    bitmapImageRep = [NSBitmapImageRep class];
+    e = [[self representations] objectEnumerator];
+    while ((rep = [e nextObject]) != nil) {
+        if ([rep isKindOfClass: bitmapImageRep])
+            break;
+        rep = nil;
+    }
+
+    if (!rep)
+        rep = [NSBitmapImageRep imageRepWithData: [self TIFFRepresentation]];
+
+    return (NSBitmapImageRep *)rep;
+}
+
+@end

PTYScrollView.m

@@ -35,9 +35,12 @@
 #import <iTerm/PTYScrollView.h>
 #import <iTerm/PTYTextView.h>
 #import <PreferencePanel.h>
+#import <Cocoa/Cocoa.h>
 @implementation PTYScroller
+@synthesize hasDarkBackground;
+
 - (id)init
 {
     userScroll=NO;
@@ -97,6 +100,31 @@
     return [super hitPart];
 }
+- (void)drawRect:(NSRect)dirtyRect {
+    if (IsLionOrLater() && self.hasDarkBackground) {
+        NSImage *superDrawn = [[NSImage alloc] initWithSize:NSMakeSize(dirtyRect.origin.x + dirtyRect.size.width,
+                                                                       dirtyRect.origin.y + dirtyRect.size.height)];
+        [superDrawn lockFocus];
+        [super drawRect:dirtyRect];
+        [superDrawn unlockFocus];
+        
+        NSImage *temp = [[NSImage alloc] initWithSize:[superDrawn size]];
+        [temp lockFocus];
+        [superDrawn drawAtPoint:dirtyRect.origin
+                       fromRect:dirtyRect
+                coreImageFilter:@"CIColorControls"
+                      arguments:[NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithDouble:0.5], @"inputBrightness", nil]];
+        [temp unlockFocus];
+        
+        [temp drawAtPoint:dirtyRect.origin
+                 fromRect:dirtyRect
+                operation:NSCompositeCopy
+                 fraction:1.0];
+    } else {
+        [super drawRect:dirtyRect];
+    }
+}
+
 @end
 @implementation PTYScrollView

PTYTextView.m

@@ -66,6 +66,7 @@ static const int MAX_WORKING_DIR_COUNT = 50;
 // Minimum distance that the mouse must move before a cmd+drag will be
 // recognized as a drag.
 static const int kDragThreshold = 3;
+static const double kBackgroundConsideredDarkThreshold = 0.5;
 // When drawing lines, we use this structure to represent a run of cells  of
 // the same font, color, and attributes.
@@ -113,6 +114,10 @@ static NSImage* bellImage = nil;
 static NSImage* wrapToTopImage = nil;
 static NSImage* wrapToBottomImage = nil;
+static CGFloat PerceivedBrightness(CGFloat r, CGFloat g, CGFloat b) {
+    return (RED_COEFFICIENT * r) + (GREEN_COEFFICIENT * g) + (BLUE_COEFFICIENT * b);
+}
+
 @interface Coord : NSObject
 {
 @public
@@ -425,6 +430,9 @@ static NSImage* wrapToBottomImage = nil;
     [defaultBGColor release];
     [color retain];
     defaultBGColor = color;
+    PTYScroller *scroller = (PTYScroller*)[[[dataSource session] SCROLLVIEW] verticalScroller];
+    BOOL isDark = ([self _perceivedBrightness:color] < kBackgroundConsideredDarkThreshold);
+    [scroller setHasDarkBackground:isDark];
     [self setNeedsDisplay:YES];
 }
@@ -4477,10 +4485,6 @@ static double EuclideanDistance(NSPoint p1, NSPoint p2) {
     return newRuns;
 }
-static CGFloat PerceivedBrightness(CGFloat r, CGFloat g, CGFloat b) {
-    return (RED_COEFFICIENT * r) + (GREEN_COEFFICIENT * g) + (BLUE_COEFFICIENT * b);
-}
-
 - (double)_perceivedBrightness:(NSColor*) c
 {
     return PerceivedBrightness([c redComponent], [c greenComponent], [c blueComponent]);