Name
ccontext:PushGroup -- push group
Synopsis
ccontext:PushGroup()
Function
Temporarily redirects drawing to an intermediate surface known as a group. The redirection lasts until the group is completed by a call to ccontext:PopGroup() or ccontext:PopGroupToSource(). These calls provide the result of any drawing to the group as a pattern, (either as an explicit object, or set as the source pattern).

This group functionality can be convenient for performing intermediate compositing. One common use of a group is to render objects as opaque within the group, (so that they occlude each other), and then blend the result with translucence onto the destination.

Groups can be nested arbitrarily deep by making balanced calls to ccontext:PushGroup() / ccontext:PopGroup(). Each call pushes/pops the new target group onto/from a stack.

The ccontext:PushGroup() function calls ccontext:Save() so that any changes to the graphics state will not be visible outside the group. The pop_group functions call ccontext:Restore().

By default the intermediate group will have a content type of #CAIRO_CONTENT_COLOR_ALPHA. Other content types can be chosen for the group by using ccontext:PushGroupWithContent() instead.

As an example, here is how one might fill and stroke a path with translucence, but without any portion of the fill being visible under the stroke:

 
cr:PushGroup()
cr:SetSource(fill_pattern)
cr:FillPreserve()
cr:SetSource(stroke_pattern)
cr:Stroke()
cr:PopGroupToSource()
cr:PaintWithAlpha(alpha)

Inputs
none

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