rc-knobs

Renders a react knob component that can be widely customised.

Installation

npm install rc-knob
yarn add rc-knob

Examples

https://eskimoblood.github.io/rc-knob/

Usage

The main idea is to split the user interaction and value calculation from the actual rendering of typical knob elements like pointer, scale or value. So all logic is done in the Knob component which is the root component. All visual UI is done in one of this components: Arc, Pointer, Scale and Value. All UI elements are rendered as SVG.
All the UI component don't to anything beside rendering and are useless on their own as they need a bunch of props that they get from the parent Knob component to render the current value of the knob. A simple knob with a pointer and value would look like this:

import React from 'react'
import { Knob, Pointer, Value } from 'rc-knob'

export default ()=> (
    <Knob>
        <Value />
        <Pointer width={1} height={2}/>
    </Knob>
)

API

Knob

The Knob component is root component that handles all the user interactions. I does not render any visual UI elements but an <div><svg></svg></div>. All children will be added to the <svg> element. It handles the user interaction by mouse, mouse wheel and keyboard arrow keys. It is accessible by keyboard using tab.

Props

angleOffset

Offset of the start angle in degree of the knob. The default is 0 which will be the top of the circle.

angleRange

Angle of the range in degree. By default its 360.

ariaLabelledBy

Will be added as aria-labelledby to the knob main element.

ariaValueText

Will be added as aria-valuetext to the knob main element.

children

Can be any of Arc, Pointer, Scale and Value. Also multiple components of the same type can be added. Beside that, any SVG element including filter can be rendered.

className

Will be added to the knob main element.

max

Max value of the knob.

min

Min value of the knob.

onChange

Callback that will pass the value when user interact with the knob.

size

Width and height of the knob in px

snap

Indicates if the knob should snap to a step. Has only an effect if steps is set. Is false be default.

steps

Number of steps the knob can snap to. It's also used to calculate the single steps for the Scale component.

value

Value of the knob

Arc

Renders an arc that indicates the current knob value.

Props

arcWidth

Width of the arc. The arc will expand to the centre.

background

Color of the arc over the whole range of the knob. If background is not set, the background arc will not rendered.

color

Color of the arc that indicates the value of the knob.

radius

Outer radius of the arc. Will be the knob size by default

Pointer

Pointer of the knob. Can be either be a SVG rect or circle depending on the passed type prop or any SVG element that is passed as a children.

Props

children

Can be any SVG element or a component that will render a SVG element. If you pass a component the percentage of the current value will be passed as a prop.
The element will be rendered as pointer. Note, that you have to pass width and height as props to make calculate the correct position.

className

Will be added to the rect, circle or the children.

color

color prop passed to the rect, circle element if type is selected.

height

Height of the rect or the custom element. Will be ignored for circle. Will be the same as width if not set.

radius

Outer radius of the circle the pointer sits on.

type

Can be rect or circle. Will render the according SVG element. width and|or height props needs to be set.

width

Width of the rect or the custom element. Radius when type is set to circle.

Scale

Renders a radial scale. The number of ticks is set by the step prop of the parent Knob component. The single scale tick can be a SVG rect or circle. Additionally a render function can be passed as a prop, that will render each tick. This is useful if the scale ticks should have different colors, or different tick length for every 10th tick for example.

Props

type

Can be rect or circle, default is rect. Will render the according SVG element. tickWidth and|or tickHeight props needs to be set.

radius

Outer radius where the ticks ends.

tickWidth

Width of a single tick. Used as radius if type is circle.

tickHeight

Height of a single tick. Is ignored when type is circle.

color

Will be passed as color prop to the render SVG element of a tick or to the custom render function.

activeColor

color for the tick that indicates the same value as the current knob value.

className

Will be passed as prop to the render SVG element of a tick or to the custom render function.

activeClassName

className for the tick that indicates the same value as the current knob value.

fn

Function that can be used to have the full control over how a tick is rendered. The function needs to return a SVG element. The function will get the following props passed: active, activeClassName, activeColor, angleOffset, center, className, color, stepSize, tickHeight, translateX, translateY, tickWidth. Most of them are just passed down from the Pointer or the Knob. Additionally are center the half of the size of the Knob , stepSize the size of the angle of one step in degree, translateX, translateY that are needed to put the tick on the correct position using the transform prop e.g: transform={`translate(${translateX} ${translateY})`} and i which is the index of the current tick.

Value

Render the current value as SVG text element.

Props

decimalPlace

Number of decimal places the value should rendered with. Is 0 by default.

className

className that is passed to the SVG text component.

marginBottom

Useful to adjust the horizontal position of the text inside of the Knob.