object.canvas

Overview

This group is a special offscreen group that enables you to draw on the snapshot's texture without redrawing the objects in snapshot.group.

Syntax

snapshot.canvas

Canvas-style Invalidation

Normally, snapshot invalidates causes the texture to be cleared prior to rendering the snapshot group's children to a texture.

In contrast, when the canvas is invalidated, they render to the texture without clearing the texture first.

To invalidate the canvas, simply pass the "canvas" parameter to snapshot:invalidate() as shown in the example below.

Canvas Properties

Properties of the canvas will be ignored and will not effect on the rendered result.

Instead, for rendering purposes, the properties of snapshot.group will be used instead.

For example, properties like position (or rotation, scale, alpha, etc) will be taken from the snapshot's group property, instead of from the canvas property.

In addition, changes to the snapshot.canvas will be reset to the corresponding value of snapshot.group just prior to when the canvas objects are drawn.

Canvas Groups vs Normal Groups

The canvas group behaves just like a normal group except:

• This group cannot be inserted into another group.
• This group cannot be removed, for example via removeSelf().
• This group has no parent.

Example

local w,h = display.contentWidth,display.contentHeight 
local snapshot = display.newSnapshot( w, h )

local brush = display.newImage( "brush.png" )
snapshot.canvas:insert( brush )

snapshot:invalidate( "canvas" )