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Elias Naur
3af01a3f43
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>
60 lines
2.0 KiB
Go
60 lines
2.0 KiB
Go
// SPDX-License-Identifier: Unlicense OR MIT
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// Package material implements the Material design.
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//
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// To maximize reusability and visual flexibility, user interface controls are
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// split into two parts: the stateful widget and the stateless drawing of it.
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//
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// For example, widget.Clickable encapsulates the state and event
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// handling of all clickable areas, while the Theme is responsible to
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// draw a specific area, for example a button.
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//
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// This snippet defines a button that prints a message when clicked:
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//
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// var gtx layout.Context
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// button := new(widget.Clickable)
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//
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// for button.Clicked(gtx) {
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// fmt.Println("Clicked!")
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// }
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//
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// Use a Theme to draw the button:
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//
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// theme := material.NewTheme(...)
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//
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// material.Button(theme, "Click me!").Layout(gtx, button)
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//
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// Customization
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//
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// Quite often, a program needs to customize the theme-provided defaults. Several
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// options are available, depending on the nature of the change.
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//
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// Mandatory parameters: Some parameters are not part of the widget state but
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// have no obvious default. In the program above, the button text is a
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// parameter to the Theme.Button method.
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//
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// Theme-global parameters: For changing the look of all widgets drawn with a
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// particular theme, adjust the `Theme` fields:
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//
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// theme.Color.Primary = color.RGBA{...}
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//
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// Widget-local parameters: For changing the look of a particular widget,
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// adjust the widget specific theme object:
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//
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// btn := material.Button(theme, "Click me!")
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// btn.Font.Style = text.Italic
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// btn.Layout(gtx, button)
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//
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// Widget variants: A widget can have several distinct representations even
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// though the underlying state is the same. A widget.Clickable can be drawn as a
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// round icon button:
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//
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// icon := material.NewIcon(...)
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//
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// material.IconButton(theme, icon).Layout(gtx, button)
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//
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// Specialized widgets: Theme both define a generic Label method
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// that takes a text size, and specialized methods for standard text
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// sizes such as Theme.H1 and Theme.Body2.
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package material
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