Inverted masks

Author: jeffrafter

creating-an-inverted-mask-layer-osx.md

@@ -0,0 +1,81 @@
+# Creating an inverted mask layer
+
+* Also known as removing a path from layer.
+
+There are several ways to accomplish this. In fact here are 5 of them: [http://www.cocoawithlove.com/2010/05/5-ways-to-draw-2d-shape-with-hole-in.html](http://www.cocoawithlove.com/2010/05/5-ways-to-draw-2d-shape-with-hole-in.html). Most solutions boil down to:
+
+* Create the whole path yourself and wrap around (this is a pain and can bug out if there are multiple regions like a star)
+* Do everything using a CGImageRef (this is just slow)
+* Use cool tricks with "even-odd" rendering (this would work great if there weren't multiple overlapping regions)
+* Just use rectangles (obvious limitations)
+
+My solution uses a subclass of a CAShapeLayer.
+
+When you subclass a CAShapeLayer the most difficult challenge is getting it to display correctly. For a subclass to call `drawInContext` you must set the `bounds`. When you set the `bounds` the position freaks out. When you want to update... you need to update the `bounds` (which means you have to *change* the value).
+
+Keeping this in mind, I created a subclass:
+
+    @interface CAInvertedMaskLayer: CAShapeLayer
+    
+    @property (nonatomic, assign) CGPathRef invertedMask;
+
+    @end
+
+    @implementation CAInvertedMaskLayer
+
+    - (void)drawInContext:(CGContextRef)ctx {
+		// Custom drawing code goes here
+        NSColor *color = [NSColor redColor];
+        
+        // Draw the path of this layer first (draws everything)
+        CGContextSetFillColorWithColor(ctx, color.CGColor);
+        CGContextAddPath(ctx, self.path);
+        CGContextFillPath(ctx);
+
+		// Clear out the inverted portion
+        if (self.invertedMask) {
+            CGContextSetBlendMode(ctx, kCGBlendModeClear);
+            CGContextSetFillColorWithColor(ctx, [NSColor clearColor].CGColor);
+            CGPathRef path = self.invertedMask;
+            CGContextAddPath(ctx, path);
+            CGContextFillPath(ctx);
+        }
+    }
+
+    - (BOOL)needsDisplayOnBoundsChange {
+        return YES;
+    }
+
+    @end
+
+So far so good. Unfortunately when I added my special drawing code, the inherited `CAShapeLayer` was still performing some actions, because of this you want to make sure you haven't set things like `fillColor` on the layer to the wrong value. Generally you want the layer `fillColor` to be `clearColor` otherwise the blending may be confusing.
+    
+    self.regionLayer = [[CAInvertedMaskLayer alloc] init];
+    self.regionLayer.fillColor = [NSColor clearColor].CGColor;
+
+You have to set the position when we override `drawInRect`. Here I am just setting the position based on the bounds of the container (in this case my view).
+
+	// Set the position, because the origin defaults to center, center
+    [self.regionLayer setPosition:CGPointMake([self bounds].size.width/2, [self bounds].size.height/2)];
+
+At this point you can simply set the `path` and update the `invertedMask` path.
+
+    CGPathRef regPath = CGPathCreateWithRect(rect, &CGAffineTransformIdentity);
+    self.regionLayer.path = regPath;
+    CGPathRelease(regPath);
+
+    CGMutablePathRef occlusionPath = CGPathCreateMutable();
+    CGAffineTransform transform = CGAffineTransformMakeScale(1, -1);
+    transform = CGAffineTransformTranslate(transform, 0, - self.bounds.size.height);
+    CGPathAddRect(occlusionPath, &transform, bounds);
+    self.regionLayer.invertedMask = occlusionPath;
+    CGPathRelease(occlusionPath);
+
+Now the tricky part: to make the render happen you need to set the bounds of the layer. Again, my layer is full width so I am just using the bounds of my view. I set it to an empty rectangle and set it back.
+
+    self.regionLayer.bounds = CGRectNull;
+    self.regionLayer.bounds = self.bounds;
+
+# Future directions
+
+Instead of using a path for the `invertedMask` you could use a whole `invertedMaskLayer`. Instead of rendering the path in your `drawInRect` code you could render the whole layer as clear. Using this you could end up with much more advanced masks.

setting_up_a_new_dev_machine.md

@@ -20,6 +20,7 @@
 * Turn off auto-correct (System Preferences | Keyboard | Text)
 * Turn up key repeat
 * Screen auto-off in 5 minutes
+* Karabiner: (customize everything) https://pqrs.org/osx/karabiner/document.html.en
 
 ## 1Password?