mirror of
https://git.sr.ht/~eliasnaur/gio
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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>
44 lines
1.0 KiB
Go
44 lines
1.0 KiB
Go
// SPDX-License-Identifier: Unlicense OR MIT
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package widget
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import (
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"image"
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"gioui.org/f32"
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"gioui.org/layout"
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"gioui.org/op"
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"gioui.org/op/clip"
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"gioui.org/op/paint"
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"gioui.org/unit"
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)
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// Image is a widget that displays an image.
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type Image struct {
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// Src is the image to display.
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Src paint.ImageOp
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// Scale is the ratio of image pixels to
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// dps. If Scale is zero Image falls back to
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// a scale that match a standard 72 DPI.
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Scale float32
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}
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func (im Image) Layout(gtx layout.Context) layout.Dimensions {
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scale := im.Scale
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if scale == 0 {
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scale = 160.0 / 72.0
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}
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size := im.Src.Rect.Size()
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wf, hf := float32(size.X), float32(size.Y)
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w, h := gtx.Px(unit.Dp(wf*scale)), gtx.Px(unit.Dp(hf*scale))
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cs := gtx.Constraints
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d := cs.Constrain(image.Pt(w, h))
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var s op.StackOp
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s.Push(gtx.Ops)
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clip.Rect{Rect: f32.Rectangle{Max: layout.FPt(d)}}.Op(gtx.Ops).Add(gtx.Ops)
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im.Src.Add(gtx.Ops)
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paint.PaintOp{Rect: f32.Rectangle{Max: f32.Point{X: float32(w), Y: float32(h)}}}.Add(gtx.Ops)
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s.Pop()
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return layout.Dimensions{Size: d}
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}
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