[cairo] Re: drawlist type functionality?

Mike Emmel mike.emmel at gmail.com
Mon Apr 4 16:17:47 PDT 2005

I'm getting the cairo list as a digest I  changed that so 
I can respond correctly qouted..

pete at shinners.org---->
I've got to study up on the Cairo API a bit more, although I see it's
getting some good reorganization at the moment.

I'm curious to see what sort of data is temporarily created as the
drawing calls are made. In the future it could be spectacular to save
these structures and recycle them on repeated calls. Although I'm not
certain this is entirely possible since the Cairo context can be
configured for just about anything before the drawlist is called. These
are also likely backend specific.
<---pete at shinners.org

Your right the reuse code would probably be backend specific but 
thats okay it can be handled in the engine.

pete at shinners.org---->
I was thinking the drawlists could be recorded as a custom backend.
Again, I want to get more comfortable with the API before getting into
this. Coming from the python end..

       # create a "bowtie" context
       ctx = cairo.Context()
       drawlist = cairo.Drawlist()
       ctx.move_to(0, 0)
       ctx.line_to(1, 1)
       ctx.line_to(1, 0)
       ctx.line_to(0, 1)
<----pete at shinners.org

I was thinking of a two level system immutable draw objects and
containers for those that can be edited thus you would create a draw
list thats immutable and it would be added to a "container" that
allowed you to add removed drawlists and apply some rules for there
interaction probably for example all members of a  container whould
share the same cario context for example. Thats where reinitializing
the context becomes interesting.

So out would havea draw list container that handled "global"
information and you could add remove the drawLists. These lists are
reference counted and can exist in multiple containers.

For example..

      # create a "bowtie" context
       ctx = cairo.Context()
       DrawContainer con = cairo.drawContainer(ctx)
       container.setBounds(0,0,5000,5000)  //max size
       container.setViewport(0,0,500,500) // visible size
       container.setClip(0,0,100,100) // current drawing area
       drawlist = cairo.Drawlist()
       drawlist.move_to(0, 0)
       drawlist.line_to(1, 1)
       drawlist.line_to(1, 0)
       drawlist.line_to(0, 1)
     //add drawlist with x y offset could be a affine transform 
     id= container.draw(drawlist,20,20)
    //reset the container clip
     container.setClip( 10,10,10,10)
     drawlist2 = cairo.DrawList()
     id2= container.add(drawList2)

    and you can do a 
   or a 
   etc ...
   even potentially loops or animation requests.

Containers themselves can be drawlists so they can be nested..
They extend drawlists to allow the addition of child drawlists in
addition they probably should support scrolling in some way or at
least a viewport

So Container would have container methods of


So you have attributes at the container level applied to all the
drawlists. The drawlists themselves have attributes container position etc.
You could potentially have ways to override the attributes. 

The resemblence to some concepts in SVG is pure coincedence :)
Actually the core of a SVG engine is probably a good starting point.

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