On Tue, 12 Jun 2001, Cyrille Chepelov wrote:
> Le mar, jun 12, 2001, à 01:53:50 -0500, Lars Clausen a écrit:
>> A third idea I came up with for this: Have the renderer only define the
>> most basic shapes as fixed function pointers, and everything else
>> (rectangles, arrows, polylines, even complete shapes if the renderer
>> wants) be in a hashtable. Then things like Visio or Kivio export can
>> try to retain more complex objects through a plug-in.
>
> I'm not sure I understand what you want to do... basically, do you want
> objects, in their draw routine, to do stuff like:
>
> def mycoolobject_draw(self,renderer):
> if renderer.ops.extra.has_key("mycoolobject"):
> renderer.ops.extra["mycoolobject"](renderer,self)
> return
> #else:
>
> <do normal processing using primitives>
> ?
Preferably have the render check outside the objects own draw routine:
char *typename = obj->get_type()->name;
if (renderer.ops.extra.has_key(typename))
renderer.ops.extra["typename"](renderer,obj);
else
renderer.ops.draw(renderer,obj);
The problem is to limit the time spent doing lookup for this. The good
part is that it is flexible enough to allow complex shapes being rendered
this way.
> What I was thinking was more something like:
> def roundedrectangle_draw(self,renderer):
> # set up line styles, etc.
> featurehint = (FEATURE_ROUNDED_RECTANGLE,
> (self.rect,self.corner_radius))
> renderer.ops.begingroup(renderer, GROUP_TYPE_FEATURE, featurehint)
> # if the renderer knows about rounded rectangles, it'll hijack
> # the rendering until endgroup() is called. Otherwise it'll
> # write the primitives as asked by the object.
>
> for corner in [nw,se,sw,ne]:
> renderer.ops.draw_arc(...)
> for border in [n,w,s,e]:
> renderer.ops.draw_line(...)
> renderer.ops.endgroup(renderer,GROUP_TYPE_FEATURE, featurehint)
That could work, though it's somewhat messy.
> Then, unlinke Python, C has a very efficient built-in way to make a hash
> table associating an identifier to snippets of executable code: a switch
> statement. Hint-using renderers just have to put a
> switch (type) {
> /* ... */
> case GROUP_TYPE_FEATURE: {
> FeatureStruct *fs = (FeatureStruct *)hint;
> switch(fs->feature) {
> case FEATURE_ROUNDED_RECTANGLE:
> disable_rendering(renderer);
> do_rounded_rectangle(fs->....);
> break;
> }
> break;
> }
> if they provide a begin_group() hint routine.
That's exactly what I want to avoid. That inner case could be quite long.
-Lars
--
Lars Clausen (http://shasta.cs.uiuc.edu/~lrclause) | Hårdgrim of Numenor
"I do not agree with a word that you say, but I | Retainer of Sir Kegg
will defend to the death your right to say it." | of Westfield
--Evelyn Beatrice Hall paraphrasing Voltaire | Chaos Berserker of Khorne
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