People with graphic tablets should already know about brush dynamics – it's one of the big advantages of using a graphics tablet.

But for those of us with only a mouse, brush dynamics are... well not very useful. The big exception is stroking paths.

How to Stroke a path with Brush Dynamics
First, Brush Dynamics is one of the options in the tool options dialog box for all of the Paint Tools – the tools highlighted with yellow in the screen shot below. I've selected the Paintbrush tool. In the tool options dialog box, click the plus box in front of Brush Dynamics to expand it and see the options as shown in the green area. I'll explain these in the next section.


To stroke a path with brush dynamics, select the Stroke with a paint tool option. Select a paint tool – Paintbrush is the one I usually use, but feel free to play with other tools. Be sure to check the Emulate brush dynamics box – otherwise you won't get any of the dynamics effects.

Brush Dynamics Options

Pressure: The pressure starts at zero at the beginning of the path, quickly builds to full pressure, and then at the end of the path it drops back to zero. The following picture shows the effect when each of the individual boxes is checked.

Note: Color option takes the color from the currently active gradient. In these examples I used the standard “FG to BG (RGB)” gradient with Black as the foreground color and Dark Blue as the background color.



Velocity: I found velocity confusing until I realized that it was emulating the effects of an airbrush or can of spray paint. The velocity starts at zero, so the paint is being sprayed very heavily at the start of the path, making a big blob. As the brush starts moving down the path, the velocity increases and the paint line becomes thinner and lighter. Eventually the velocity is fast enough that the paint becomes virtually transparent. Here is the effect from checking the individual boxes.



Random: This one is what you might expect. The value jumps randomly within the range of full on to completely off.



And here is a screen shot showing the paths I used to create the above images:



Other Crib Sheets

This a crib sheet I created a couple of years ago with the effects that interested me the most. That crib sheet was made using GIMP 2.6.8. I just repeated it with GIMP 2.6.12 and I got slightly different results.



I haven't used 2.7 or 2.8 yet, so I don't know how they perform. (I'm waiting for a relatively bug-free version before I make the move to 2.8.)

Using Brush Dynamics

Here are some simple examples, rendered in GIMP 2.6.12 with standard brushes and gradients.



Several days ago I posted this crib sheet that I made for creating rocket trails using paths and brush dynamics. I think it is my rendition of a tutorial that I saw, but this file is almost two years old... The brush is one of the Animated Smoke brushes by LJFHutch and it is available on deviantART: http://ljfhutch.deviantart.com/art/Gimp ... -162129054 (He has a number of other interesting brush sets that you might want to check out.)




An Important Reminder: Reset your brush parameters when you are done! The easiest way is to use the reset button in the lower right corner of the brush options page.

Edit: Corrected the color gradient description for the examples; removed the help forum block at the beginning.

Nice info bhk; like the rocket/missile trail too.

great post, awesome stuff!

An excellent tutorial. I touched on this in a previous thread as I had discovered the technique as a result of not being accurate enough with my tablet. It's a great technique and this tute demonstrates it really well. Thank you.

Moved to tutorials and stickied.
Thanks for sharing it.

I'm glad people are finding this useful.

Rod, thanks for the sticky.

Thanks a bunch for taking me seriously about doing a tut on this. Great stuff! I now have some new crib sheets to play with. What I wanted to do is create a brush that will do something similar to what you see when you use the Glossy Stroke filter. Tapered on the ends fading to transparent with a little jitter to make it look random. Hard to explain actually. I'll check out that link for sure. Thanks again.

Excellent tutorial!
In GIMP 2.8 brushes and dynamics are much more configurable than 2.6, so this you explain here becomes very powerful in GIMP 2.8.

You can also use color from a gradient that contains transparency, like "FG to Transparent" (or make your own).