.. meta::
   :description:
        The Curve Brush Engine manual page.

.. metadata-placeholder

   :authors: - Wolthera van Hövell tot Westerflier <griffinvalley@gmail.com>
             - Raghavendra Kamath <raghavendr.raghu@gmail.com>
             - Scott Petrovic
             - ValerieVK
   :license: GNU free documentation license 1.3 or later.

.. index:: Brush Engine, Curve Brush Engine
.. _curve_brush_engine:

==================
Curve Brush Engine
==================

.. image:: /images/icons/curvebrush.svg

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.


.. image:: /images/brushes/Krita-tutorial6-I.1-1.png

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?

.. image:: /images/brushes/Krita-tutorial6-I.1-2.png

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.

.. image:: /images/brushes/Krita-tutorial6-I.2-1.png

* 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.

.. image:: /images/brushes/Krita-tutorial6-I.2-2.png

* 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:

.. image:: /images/brushes/Krita-tutorial6-I.2-3.png

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

.. image:: /images/brushes/Krita-tutorial6-I.2-4.png