For many images with alpha layers the returned values would be a complex
set of points, and for some discontiguous.
If the purpose for obtaining that collection of points is to determine
whether a click at a specific location would be inside or outside the
control's region(s), that would require a lot of calculations, taking
non-trivial development time to write and a fair bit of CPU time to
execute in script.
It may be simpler and more efficient to let the engine do that
calculation using existing functions built into the engine.
See the Dictionary entries for:
- "within" function - describes how the clickable region is calculated
and will serve the majority of use-cases well.
- "intersect" function - which goes further to allow the scripter to
optionally define an alpha channel threshold.
--
Richard Gaskin
Fourth World Systems
Quentin Long wrote:
In the past few List digests, there's been some discussion of practical issues
regarding when a click does or doesn't count as clicking *on* a particular
item. So, here's a proposed addition to LiveCode…
=============
Name: clickableRegion
Recognized abbreviation: clickReg
"clickableRegion" is a proposed property of anything in a stack that might a
user might reasonably be expected to click on—controls, that is. We're talking buttons,
fields, graphics, images, yada yada yada.
The clickableRegion of a control is a return-delimited list of points that
define a region of the screen. Since clickableRegion is a property of a
control, the engine's internal representation of these points should probably
use the location of the control as the origin (the 0,0 point) for the
clickableRegion's points.
Any click whose clickLoc is within the area defined by a control's
clickableRegion, will be treated by the engine as if it were a click on that
control.
The default value of a control's clickableRegion should be determined by that
control's visible-on-screen pixels—for fields, this should be the field's
rectangle; for graphics, this should be the points of the graphic; and so on
and so forth.
The clickableRegion property should be both get-able and set-able. If you clear the
clickableRegion (such as by setting it to ""), it should revert back to its
default value.
Since clickableRegion can be set to arbitrary values, it may well happen that 2
or more controls have overlapping clickableRegions. This may not be a problem
if the engine can simply make use of whatever magic it does when it handles
clickLocs which fall within the rects of 2+ overlapping buttons. If the
engine's existing 'click-disambiguation' machinery does not suffice to
determine which control an ambiguous click is meant for, go with the control
that has the highest-value layer property.
=============
Thoughts/comments/complaints?
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