Re: [Geotools-devel] Thinking about Tools

[Andrea A. <aa...@li...>]

Hi everybody,
I'd like to share by thougths on this subject too... I've read the logs, and of course
Cameron's mail. And I feel the need to have a better understanding... So, here are
my thoughts (and questions...)

Since we need to support various input devices, and we also need to consider
that even standard gui have different ways of providing "event" that the
map control need to process, there should be at least:
a) an event source manager: something that processes the real inputs, whatever they are,
    and converts them to a standard intermediate command;
b) an command processor: something that processes the intermediate command and
    does the real work.

Part a) is device dependent, and does not need uniform interfaces. The uniform part
is all in b). Now, different devices will have different way to simulate mouse events and
provide commands. Let's consider a real action: a user drags a zoom window. 
The widget should respond by drawing the current selected window until the user
releases the mouse. This informations should be provided by means on PointTriggers,
isn't it? Which also mean that PointTriggers work with device coordinates, not geographical
ones. The MapPane accept the PointTrigger and forwards it to every active Tool, which
may or may not trigger some Action. 
Now, there are a couple of things that I probably don't understand in Cameron
list: in the same list we find MouseEvents and PointTriggers, but they are at a different
leve: a MouseEvent is triggered by the standard Swing event handling mechanism thru
the MapPane widget, should be handled outside it by a MouseEventProcessor, I guess,
which issues PointTriggers, which are passed back to the MapPane thru a
processPointTrigger method (or some other name), which forwards them to the active
Tools, and so on... right? Or not? Or is the control chain completely outside the MapPane
widget? 

Anyway, the tools will transform device coordinates into geographic ones and 
create Actions. Two questions:
* this way mutliple tools will trasform more than once the device coordinates into
  geographics ones. Should we pass to tools PointTriggers in geographics coordinates? 
  Maybe in both formats (device and geographic?)
* are these Actions subclasses of the Swing Action class?
Hope so, since otherwise this would be really confusing for people used to Swing
guis. Moreover, Actions could be triggered by toolbar buttons, menu or keyboard
shortcuts, and in this case there is no need for the PointTrigger, it's just a "zoom 10% more"
or "pan 1/25 of the current display size to the right". Which applies also to vocal
commands and gestures, I think many of this would be a direct command, such as
a zoom, so in some way the gesture processor should be connected directly to 
Actions too...

In this picture, what is the place for a MouseTool? Isn't the mouse event handling
already processed by component listed in point a) above?

Andrea