Simple Use

The simplest use is to fill an area defined by two different objects. Select the Paint Bucket Tool ( icon , Shift+F7) from the Tool Box and then click in the overlapping region. A new object is created with the current Fill color.

Paint Bucket - Simple Use.
Left: Before Paint Bucket fill. Right: After clicking on the overlapping region with the Paint Bucket Tool (with the Fill color set to red).

The cursor position when clicking determines the starting point of the fill region. The filling algorithm recursively adds neighboring areas to the region until pixels are found that don't meet the criteria determined by the parameters in the Tool Controls.

The Threshold parameter controls how close a color must match the color (or Alpha) under the cursor. Lower thresholds will match a smaller range.

Paint Bucket - Threshold.
The gray areas have been filled by clicking on the centers of the rectangles with the Paint Bucket Tool. From left to right, the Threshold parameter was set to 5, 10, 20, and 40.

The Fill by parameter controls what color value is used to determine the the color matching. Choices are: Visible Colors (default), Red, Blue, Green, Hue, Saturation, Lightness, and Alpha.

Paint Bucket - Channels.
The circles were first filled with a blue to green gradient. The gray areas were created with the Paint Bucket Tool by clicking on the centers of the circles. In both cases, the Threshold parameter was set to 10. The Fill by parameter was set to Visible Colors on the left and Red on the right. With a value of Red the blue and green of the circle are ignored in the color matching, thus the bucket fill area reaches the circle's edge where there is a large change in the red level.

Holding the Ctrl down while clicking on an object with the Paint Bucket Tool will set the Fill and Stroke to the current style without preforming any filling.