On Thu, 8 Jun 2006 17:40:21, Rick Mann <email@hidden> wrote:
> I've brought this subject up before, and I usually get convinced of
> the right way to do it. Then I get distracted from this project for
> months, and forget it all. So, here it is again:
>
> I am developing a non-trivial CAD application. It supports many
> different tools, so I have a "mouse handler" architecture: an
> instance of the current tool is set to be current, and mouse events
> are sent to it for handling.
>
> In some tools, keys can be pressed during button-down periods. For
> this reason, I don't want to use TrackMouseLocation(); I'd rather
> maintain state, and let key events be handled appropriately.
>
> A great deal of drawing takes place in response to mouse events. Just
> pointing at an object on the canvas can result in drawing as it's
> highlighted, for example.
>
> To complicate matters, there is an almost-always non-identity
> transform applied; the user can zoom in and pan all over the canvas,
> and clicking needs to be translated into canvas coordinates (inverse
> of the CG context's transform).
>
> My understanding from past experience is that I really can't get the
> view's CGContext from within a mouse event (for the purposes of doing
> an inverse transformation),
Conceptually, mousing involves proper coordinates calculations,
so I'd expect CGContext to be used internally within mouse events,
maybe just not exposed... See below.
> and that I shouldn't do drawing, either.
That's true. Though if absolutely necessary, there is HIViewRender.
> I can probably live with the latter, but I really want to build my
> model during the event.
>
> The alternative is to store the last mouse position, set some state,
> ask for the view to be redrawn, and do everything in the redraw. I
> don't like this for any number of reasons.
What reasons?
Looks like a good approach.
> My biggest concern is that
> I've been told the context is unreliable during a mouse event.
That's something I don't understand: how mousing could work
properly if there is no proper CGContext (that establishes
coordinate transformations)?
Mike
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