Gradient Tool
Icon: 
Hotkey: G
Behaviour
- draws a gradient from the primary to the secondary color, or vice versa
- functions either as a brush or as a geometric gradient defined by a start- and endpoint
Actions
- Draw gradient from primary to secondary color:
- Draw gradient from secondary to primary color:
- Increment/decrement brush width: Arrow Keys or Shift + Scroll Wheel
Modifiers
- Ctrl - hold to enable geometric mode
- [in geometric mode] Shift - snap the slope of gradient to the nearest 15° angle
Tool Options
Universal
- Dithered: when turned on, the gradient colors are determined via 4x4 ordered dithering rather than linear interpolation
In brush mode
- Brush breadth: 1px - 100px
- Brush shape:
- Circle
- Square
- Line
- Angle: slope of the brush
In geometric mode
- Gradient shape:
- Linear
- Radial
- Spiral
- Bounded: when turned on, the gradient is not padded with the primary and secondary colors beyond its start- and endpoint
- Mask: when turned on, the gradient only replaces pixels within a certain color similarity threshold when compared with its starting point
- Contiguous: when turned on, candidate pixels to be replaced by the gradient must be adjacent to other pixels that have been replaced as part of the same operation
- Tolerance: determines how similar colors must be