[self-interest] clipping

[Jecel Assumpcao Jr]

On Tuesday 25 March 2003 18:05, legyxo42 wrote:
> Hi, I'm trying to clip drawing submorphs with baseBounds of
> their owner. code looks like this:
>
> drawon: aCanvas = (
> baseDrawOn: aCanvas.
> 0 = morphCount ifFalse: [| c |
>     c: (aCanvas copyOffset: position).
>     c clip: baseBounds. "is this OK?"

It is okay, but not enough since clipping is not fully implemented but 
only has some methods here and there. In particular, this line would be 
needed:

      c gc setClipRectangle: baseBounds.

Adding this line here is a disaster, unfortunately, since the graphics 
context (gc) is shared with other canvases and this will mess things 
up.

It is very natural to assume that "c clip: ..." would take care of the 
details, but it doesn't.

>     morphsReverseDo: [| :m | m drawOn: c].
> ].
> self
> )

Here is the simplest solution that will mostly work:

drawon: aCanvas = (
baseDrawOn: aCanvas.
0 = morphCount ifFalse: [| c |
    c: (aCanvas copyOffset: position).
    morphsReverseDo: [| :m | c withClip: (baseBounds translate: position 
negated)
                               Do: [m drawOn: c]].
].
self
)

This code looks good but when you move the morph the shadow still 
includes the outlines of any submorphs that are sticking out. It is 
probably easy to fix this.

Having withClip:Do: inside the loop is bad since the same old clipping 
rectangle keeps being saved and restored over and over and is always 
being replaced with the same rectangle. It would be nice to do this 
just once.

-- Jecel