Draws lines, arrows, or rulers. Click at the starting position, drag to the end position, and then release to draw a straight line. Click the ``Cancel'' button or anywhere on the top menu bar to return to normal mode.
Once set, the line drawing parameters affect all subsequent lines, boxes, sketch operations, and image borders but not curves and circles.
Transverse gradient: Changes the color across the width of a line according to the specified gradient and center color. A gradient of RGB =128,128,128 is the same as a solid color. A gradient of RGB =127,126,129 decreases the red by 1, the green by 2, and increases the blue by 1 from the top to bottom of the line. If ``Double gradient'' is selected, the starting color is the center of the line. Of course, the line width must be greater than 1 for this to work.
Arrowhead: Draws an arrow on the line with the tip at the starting coordinate. If the line width is changed, the arrow sizes change automatically to keep the arrow size proportionately constant. It is also possible to customize the arrow:
Width: the maximum width of the arrowhead
Outer length: the length of the arrowhead measured parallel to the line, from the tip to the ends of the two outer points.
Inner length: the length of the arrowhead from the tip to the point at which the arrow touches the shaft.
Skew: The number of pixels in the x direction by which the line is shifted for each unit of thickness. This is useful in sketching gradient lines.
Ruler: Adds tic marks perpendicular to line.
Ruler + numbers: Adds tic marks and graduations perpendicular to line. The graduations start at 0 and increment in the direction in which the line is created. The currently-selected font and foreground color are used. The text portion is anti-aliased so it appears smooth at any angle.
Ruler scale: Enter a factor to change the spacing between tic marks in the ruler.
Ruler tic length: Length of the small perpendicular tic marks in the ruler, in pixel units.
Note: On 8-bit displays, the colors produced by the gradient are constrained by the current colormap. If the gradient calculation needs a color that is not contained in the colormap, the closest color is used. This can result in inaccurate color gradients.