Lightweight HTML container element as a controller parent for one or more canvas elements
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What is it ... ?

canvas-area is a lightweight custom html element as a controller parent for one or more canvas elements. It allows zoom, pan and resize interactions.

Show me ...


Where is the markup code ...

<canvas-area id="ca" width="401" height="301" resizable="both">
    <canvas id="c"></canvas>


  • width: width of element in px.
  • height: height of element in px.
  • resizable: one of ['none', 'horizontal', 'vertical', 'both'].
  • cartesian: true or false

Example please ...

try it out ...

Multiple Canvases

Multiple canvases are mostly used as layers in practice. It is up to you, how you organize, what to draw on which layer. Often there is a background layer holding static graphics, which does not need to be updated frequently. In contrast to that there might be a dynamic layer holding animated graphics for instance. There also might be an interactivity layer, containing editable geometry.

Separating low frequently updated geometry from high frequently updated geometry by different layers should result in a performance gain.

Please note, when using multiple canvases - and stacking them on top of each other:

  • For every canvas element, perhaps except the first one, use position:absolute; style.
  • Stacking level can be made explicite using z-index: 5; style.
  • canvas elements are transparent by default. So avoid giving them background colors.
  • canvas-area is managing the resize of its canvas children, but not their redraw.
  • canvas-area is managing the view parameters for pan and zoom, but does not apply those values to the canvas contexes. Do that by yourself while redrawing or using the on('view',...) handler.


<canvas-area id="ca" width="401" height="301">
    <canvas id="c1" style="position:absolute; z-index:1;"></canvas>
    <canvas id="c2" style="position:absolute; z-index:2;"></canvas>

Show me the scripting API ...

canvas-area behaves as a standard html container element with known inherited DOM properties and methods. Additionally it offers properties ...

Property Type Value Default
width Number width of element in px 300 px
height Number height of element in px 150 px
resizable String one of ['none', 'horizontal', 'vertical', 'both'] 'none'
cursor String simple interface to CSS cursor attribute. 'auto'
view {x,y,scl} origin location x,y in px and scaling factor scl {0,0,1}
cartesian Boolean true: y-axis pointing up,
false: y-axis pointing down
observable Object initially (lazily) set external observable object once. -

... methods ...

Method Arguments Returns Comment
pan({dx,dy}) dx: delta x
dy: delta y
undefined origin displacement. Modifies view property
zoom({x,y,scl}) x: x-center
y: y-center
scl: factor
undefined zoom about point {x,y} by factor scl. Modifies view property
pntToUsr({x,y}) point point transform argument point (device coordinates) to result point (user coordinates) with respect to view property
notify(key,value) key: event type
value: event data
undefined notify observers of event type key about event value
on(key,handler) key: event type
handler: event handler
this register handler with event type key.

... and events, which can be observed via observe method.

Type Object Value
'pointer' {x,y,...}* User has moved the pointer.
'drag' {x,y,...}* User has moved the pointer with left button down.
'resize' {width,height} User did resize canvas-area element
'view' {x,y,scl} User modified the view property via pan, zoom, ...
'buttondown' {x,y,...}* User has pressed the pointer device's button down.
'buttonup' {x,y,...}* User has released the pointer device's button.
'pointerenter' {x,y,...}* pointer has entered the canvas-area.
'pointerleave' {x,y,...}* pointer has left the canvas-area.

{x,y,...}* custom event data object:

Property Description
x,y Pointer location in device coordinates.
dx,dy Pointer displacement in device coordinates since last pointer event.
buttons Device buttons pressed (1:left, 2: right, 4: middle button).
delta Mouse wheel delta units.


Use following link for canvas-area.js.



  • Does not work properly with Mobile Device X and Touch Screen Y ?

    • Desktop browsers only are addressed primarily at current.
    • Implementation of touch events is experimental (pan works with touch and resize also using a pen now).
    • Issues with Microsoft Edge.
  • Can you implement feature X and possibly feature Y ?

    • canvas-area serves my personal needs very well as it is.
    • So ... no, I won't.
    • Please go ahead and implement it by yourself.
    • If you think, your enhancement is of common interest, you are very welcome, to send me a pull request.


[0.4.7] on January 28, 2018

  • observable setter (only) for possibly injecting an external observable object. So enable delegating observer management to 'app' object.

[0.4.5] on January 19, 2018

  • chainable method on(key,handler) added.
  • method observe(key,handler) marked as deprecated. Use on(key,handler) instead.
  • renamed event property buttons to btn in [drag,pointer,buttondown,buttonup,pointerenter,pointerleave] event.
  • necessary styles display: block; overflow: hidden; automatically added as inline style while constructing.
  • touch events experimentally implemented.

[0.4.0] on January 06, 2018

  • Initial release.


canvas-area is licensed under the MIT License

© Stefan Gössner