Tips and Tricks
Using the File ▸ Command Bar menu item (shortcut key ⌘⇧O) will bring up a little text window you can type in to find menu commands or other hidden commands. You can also search Acorn's help documentation with this. Type "h" followed by a space and then a help topic to only search documentation. For instance, if you typed "h crop" it will return all documentation related to the crop tool. There are some entries which do not show up in the menu bar, but which can be useful: Toggle Dark Aqua, Fill Layer, Fill Layer With Stroke Color, Feather (10px radius), Use Pixels for Ruler, Toggle Stroke/Fill, Change Canvas Background, Capitalize/Lowercase/Uppercase Text.
You can create custom presets for filters, new images, and the crop tool. In order to delete a preset you have created, hold down the option key while clicking on the preset name. A window will appear to confirm that you want to delete the preset.
Changing Measurement Fields
In most text boxes that take measurements, you can use math to change the value. For instance, if you open up the canvas resize sheet and you want to double the width you can just append *2 to the width field and press tab. Division, subtraction and addition also work. You can also use the up and down arrows to increase the size by a point (or quarter inch). Hold down the shift key to increment by 10.
Using the Arrow Keys with Shapes
Did you know you can use the arrow keys to move selected shapes Acorn? And if you don't have any selected already, pressing an arrow key will select all the shapes on the current shape layer and begin moving them for you. In addition, you can hold down the shift key when pressing an arrow key to move the selected shape(s) ten pixels at a time instead of one. And if you hold down both command and option while pressing an arrow key, Acorn will move the selected shapes half a pixel for you.
Need to zoom in or out quickly? Press Command-5 once to zoom out to 50% and twice to zoom out to 25%. Command-1 will return you to 100%, command-2 will take you to 200%, and command-3 to 400%.
Holding the shift key while clicking on the canvas will draw straight lines between your clicked points with the brush. If you press the option+cmd keys when using the paint tool it will turn into an erasing brush. To change your brush size quickly, hold down both control and option on the canvas, then drag left and right with your mouse or trackpad to see the brush size grow and shrink.
You can setup one of your express buttons to map to option+cmd, so you have a quick eraser without needing to flip your stylus.
Hold down the command key when using the + button in the tool palette to add a new group layer. If you hold the option key while clicking on the layer visibility icon in the layers list (the eye!) it will hide all other layers. Option clicking on it again, will restore the previously visibility state for all other layers.
When making a gradient, hold down the shift key to constrain the gradient direction in 45° / 90° / 180° increments.
App Support Folder
Open Acorn's "App Support Folder" menu item under the Help menu to get to things like custom plugins and saved brushes.
Option-Delete will fill the current layer with whatever color is present in the color well. Opt-Shift-Delete will use the secondary color well.