Customising Snap Areas: Regions, Modifiers and the Drag Footprint

Disabling individual regions

Regions are addressed as a bit field. Each has an index; the value you write is the sum of two raised to each index you want ignored. This sounds worse than it is — the table gives you the value directly.

# just the top maximise region
defaults write com.knollsoft.Rectangle ignoredSnapAreas -int 1

# all four half-regions beside the corners: 256+512+1024+2048
defaults write com.knollsoft.Rectangle ignoredSnapAreas -int 3840

# corners only, keep the edges: 16+32+64+128
defaults write com.knollsoft.Rectangle ignoredSnapAreas -int 240

# top and bottom edges: 1+2
defaults write com.knollsoft.Rectangle ignoredSnapAreas -int 3
killall Rectangle && open -a Rectangle

Adjusting how easy a region is to hit

Rather than disabling a region outright, you can make it harder to enter. Each edge has an independent margin, defaulting to 5:

defaults write com.knollsoft.Rectangle snapEdgeMarginTop -int 20
defaults write com.knollsoft.Rectangle snapEdgeMarginBottom -int 10
defaults write com.knollsoft.Rectangle snapEdgeMarginLeft -int 10
defaults write com.knollsoft.Rectangle snapEdgeMarginRight -int 10

Counter-intuitively, a larger number here means the region is entered less easily, so this is the middle ground between leaving a region on and turning it off. Worth trying before reaching for the bit field.

Requiring a modifier key

The decisive option: snapping only occurs while a chosen modifier is held. Ordinary window dragging then never triggers anything, which makes drag-to-snap a deliberate action rather than an ambient hazard.

# hold Command to snap
defaults write com.knollsoft.Rectangle snapModifiers -int 1048576

# hold Control+Shift: 262144 + 131072
defaults write com.knollsoft.Rectangle snapModifiers -int 393216

# remove the requirement entirely
defaults delete com.knollsoft.Rectangle snapModifiers

Extra regions: sixths

Off by default. Once enabled, drag a window to a corner and then slide along the edge toward the thirds region to land on a sixth:

defaults write com.knollsoft.Rectangle sixthsSnapArea -bool true

On a 34-inch or wider display this makes a six-panel arrangement reachable by dragging, which the default region set cannot do. On a laptop it is close to useless — a sixth of a 14-inch panel is not a working area.

Restyling the drag footprint

The translucent preview shown while dragging is the app's only real visual element, and every aspect of it is configurable.

# transparency (default 0.3)
defaults write com.knollsoft.Rectangle footprintAlpha -float 0.45

# border thickness in pixels (default 2)
defaults write com.knollsoft.Rectangle footprintBorderWidth -float 3

# colour, as RGB components between 0 and 1
defaults write com.knollsoft.Rectangle footprintColor -string "{\"red\":0,\"blue\":0.5,\"green\":0.5}"

# disable the fade-out
defaults write com.knollsoft.Rectangle footprintFade -int 2

# animation duration multiplier (default 0 — no animation)
defaults write com.knollsoft.Rectangle footprintAnimationDurationMultiplier -float 1.5

Two practical reasons to change these rather than aesthetic ones. On a very bright display the default alpha can be hard to see, and raising it plus thickening the border makes the target unmistakable. On a dark theme, a colour that contrasts with your wallpaper prevents the preview disappearing into the background entirely.

Mission Control and fast upward drags

Dragging a window quickly toward the top of the screen can trigger Mission Control rather than the maximise region. This is a system gesture. It can be suppressed for fast drags while leaving slow deliberate ones working:

defaults write com.knollsoft.Rectangle missionControlDragging -int 2

# how far off-screen is tolerated, in pixels (default 25)
defaults write com.knollsoft.Rectangle missionControlDraggingAllowedOffscreenDistance -float 40

# how long the suppression lasts, in milliseconds (default 250)
defaults write com.knollsoft.Rectangle missionControlDraggingDisallowedDuration -int 400

Questions