Curve Brush Engine

The curve brush is a brush engine which creates strokes made of evenly spaced lines. It has, among other things been used as a replacement for pressure sensitive strokes in lieu of a tablet.

Settings

First off, the line produced by the Curve brush is made up of 2 sections:

• The connection line, which is the main line drawn by your mouse.

• The curve lines I think, which are the extra fancy lines that form at curves. The curve lines are formed by connecting one point of the curve to a point earlier on the curve. This also means that if you are drawing a straight line, these lines won’t be visible, since they’ll overlap with the connection line. Drawing faster gives you wider curves areas.

You have access to 3 settings from the Lines tab, as well as 2 corresponding dynamics:

• Line width: this applies to both the connection line and the curve lines.

  • Line width dynamics: use this to vary line width dynamically.

• History size: this determines the distance for the formation of curve lines.

  • If you set this at low values, then the curve lines can only form over a small distances, so they won’t be too visible.

  • On the other hand, if you set this value too high, the curve lines will only start forming relatively „late“.

  • So in fact, you’ll get maximum curve lines area with a mid-value of say… 40~60, which is about the default value. Unless you’re drawing at really high resolutions.

• Curves opacity: you can’t set different line widths for the connection line and the curve lines, but you can set a different opacity for the curve lines. With low opacity, this will produce the illusion of thinner curve lines.

  • Curves opacity dynamics: use this to vary Curves opacity dynamically.

In addition, you have access to two checkboxes:

• Paint connection line, which toggles the visibility of the connection line.

• Smoothing, which… I have no idea actually. I don’t see any differences with or without it. Maybe it’s for tablets?

Drawing variable-width lines

And here’s the only section of this tutorial that anyone cares about: pretty lineart lines! For this:

• Use the Draw Dynamically mode: I tend to increase drag to at least 50. Vary Mass and Drag until you get the feel that’s most comfortable for you.

• Set line width to a higher value (ex.: 5), then turn line width dynamics on:

  • If you’re a tablet user, just set this to Pressure (this should be selected by default so just turn on the Line Width dynamics). I can’t check myself, but a tablet user confirmed to me that it works well enough with Draw Dynamically.

  • If you’re a mouse user hoping to get variable line width, set the Line Width dynamics to Speed.

• Set Curves opacity to 0: This is the simplest way to turn off the Curve lines. That said, leaving them on will get you more „expressive“ lines.

Additional tips:

• Zig-zag a lot if you want a lot of extra curves lines.

• Use smooth, sweeping motions when you’re using Draw Dynamically with Line Width set to Speed: abrupt speed transitions will cause abrupt size transitions. It takes a bit of practice, and the thicker the line, the more visible the deformities will be. Also, zoom in to increase control.

• If you need to vary between thin and thick lines, I suggest creating presets of different widths, since you can’t vary the base line width from the canvas.

Alternative:

• Use the Draw Dynamically mode

• Set Curves opacity to 100

• Optionally decrease History size to about 30

The curve lines will fill out the area they cover completely, resulting in a line with variable widths. Anyway, here are some comparisons:

And here are examples of what you can do with this brush: