Before this change, events were typically processed twice or more per
widget: once in the Layout method for refreshing the visual state, and
once per method that queries for state changes.
One example is widget.Clickable that processed events in both its Layout
and Clicked method.
This change establishes the convention that events are processed once, in
the Layout method. There are several advantages to that approach:
- Query methods such as Clickable.Clicked no longer need a layout.Context.
- State updates from events only occur in Layout.
- Widgets are simplified because they won't need a separate processEvents
(or similar) method and won't forget to call it from methods other than Layout.
- Useless calls to gtx.Events are avoided (gtx.Events only returns events
for the first call each frame for a given event.Tag).
The disadvantage is that state updates from input events will not appear
before Layout. For example, in the call sequence
var btn *widget.Clickable
if btn.Clicked() {...}
btn.Layout(...)
the Clicked call will not detect an incoming click until the frame after it
happened.
This is ok because
- The Gio event router automatically dispatches an extra frame after events
arrive, bounding the latency from events to queries such as Clicked to
at most one frame (~17 ms).
- The potential extra frame of latency does not apply to Layout methods as long
as they process events before drawing. In other words, the visual feedback
from input events are not delayed because of this change.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Change the definition of Widget from the implicit
type Widget func()
to the explicit functional
type Widget func(gtx layout.Context) layout.Dimensions
The advantages are numerous:
- Clearer connection between the incoming context and the output dimensions.
- Returning the Dimensions are impossible to omit.
- Contexts passed by value, so its fields can be exported
and freely mutated by the program.
The only disadvantage is the longer function literals and the many "returns".
What tipped the scales in favour of the explicit Widget variant is that type
aliases can dramatically shorten the literals:
type (
C = layout.Context
D = layout.Dimensions
)
widget := func(gtx C) D {
...
}
Note that the aliases are not part of the Gio API and it is up to each user
whether they want to use them.
Finally the Go proposal for lightweight function literals,
https://github.com/golang/go/issues/21498, may remove the disadvantage
completely in future.
Context becomes a plain struct with only public fields, and its Reset is
replaced by a NewContext convenience constructor.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Instead of
type Contraints struct {
Width, Height Constraint
}
use
type Constraints struct {
Min, Max image.Point
}
which leads to simpler use. For example, the Min method is trivally replaced by
the field, and the RigidConstraints constructor is no longer a net win.
API Change. Rewrites:
gofmt -r 'gtx.Constraints.Min() -> gtx.Constraints.Min'
gofmt -r 'gtx.Constraints.Width.Min -> gtx.Constraints.Min.X'
gofmt -r 'gtx.Constraints.Height.Min -> gtx.Constraints.Min.Y'
gofmt -r 'gtx.Constraints.Height.Max -> gtx.Constraints.Max.Y'
gofmt -r 'gtx.Constraints.Width.Max -> gtx.Constraints.Max.X'
Signed-off-by: Elias Naur <mail@eliasnaur.com>
material.Clickable is useful for adding a click response to any widget
or area.
Rename widget.Button to widget.Clickable to reflect the wider use
spectrum.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Before this change, the widget.Button.Layout method assumed the caller had set
up the pointer hit area before. Further, the very common rectangular hit
areas needed both an AreaOp and a widget.Button.Layout call.
Make widget.Button less subtle and more useful by setting up a
pointer hit area given by the incoming minimum constraints.
Drop a pointer.AreaOp made redundant by the change.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
It was left over from a previous approach to enable the program
to decide the ordering between calls to Layout vs Clicked.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Determining the enabled state of a widget from whether its Clicked method has
been called only works for button-like widgets. For example, it's not clear a
Clicked method is appropriate for a CheckBox.
Remove the feature for now, and let's find a better design in the future.
As a nice side effect, we can now process events in Layout methods, so that
buttons react to user input even when Clicked is not called.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Elias Naur