The assistant system allows you to have a little help while drawing straight lines or circles.
They can function as a preview shape, or you can snap onto them with the freehand brush tool. In the tool options of free hand brush, you can toggle 'snap to assistant' to turn on snapping.
The following assistants are available in Krita:
There's several types in Krita. You can select a type of assistant via the tool options docker.
An assistant for drawing ellipses and circles.
This assistant consists of three points: the first two are the axis of the ellipse, and the last one is to determine it's width.
If you press shift while holding the first two handles, they will snap to perfectly horizontal or vertical lines. Press shift while holding the third handle, and it'll snap to a perfect circle.
This ruler takes four points and creates a perspective grid.
This grid can be used with the 'perspective' sensor, which can influence brushes.
If you press shift while holding any of the corner handles, they'll snap to one of the other corner handles, in sets.
There are three assistants in this group:
If you press shift while holding the first two handles, they will snap to perfectly horizontal or vertical lines.
This assistant allows you to position and adjust four points to create a cubic bezier curve. You can then draw along the curve, snapping your brush stroke directly to the curve line. Perfect curves every time!
If you press shift while holding the first two handles, they will snap to perfectly horizontal or vertical lines. Press shift while holding the third or fourth handle, they will snap relative to the handle they are attached to.
This assistant allows you to create a vanishing point, typically used for a horizon line. A preview line is drawn and all your snapped lines are drawn to this line.
It is one point, with four helper points to align it to previously created perspective lines.
They are made and manipulated with the Ruler Assistant Tool.
If you press shift while holding the center handle, they will snap to perfectly horizontal or vertical lines depending on the position of where it previously was.
Like the vanishing point assistant, this assistant is per a set of parallel lines in a 3d space. So to use it effectively, use two, where the second is at a 90 degree angle of the first, and add a vanishing point to the center of both. Or combine one with a parallel ruler and a vanishing point, or even one with two vanishing points. The possibilities are quite large.
This assistant will not just give feedback/snapping between the vanishing points, but also give feedback to the relative left and right of the assistant. This is so you can use it in edge-cases like panoramas with relative ease.
If you press shift while holding the first two handles, they will snap to perfectly horizontal or vertical lines. Press shift while holding the third handle, and it'll snap to a perfect circle.
Check out this in depth discussion and tutorial on YouTube
So now that you've seen the wide range of drawing assistants that Krita offers, here is an example of how using these assistants you can set up Krita for technical drawing.
This tutorial below should give you an idea of how to set up the assistants for specific types of technical views.
Orthographic is a mode where you try to look at something from the left or the front. Typically, you try to keep everything in exact scale with each other, unlike perspective deformation.
The key assistant you want to use here is the Parallel Ruler. You can set these up horizontally or vertically, so you always have access to a Grid.
All of these are set up using three Parallel Rulers.
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