widget,widget/material: move Image and Icon to widget package

There is nothing theme-specific about displaying images and icons,
so move the types from the material package to the generic widget
package.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/image.go

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package widget
+
+import (
+	"image"
+
+	"gioui.org/f32"
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/op/clip"
+	"gioui.org/op/paint"
+	"gioui.org/unit"
+)
+
+// Image is a widget that displays an image.
+type Image struct {
+	// Src is the image to display.
+	Src paint.ImageOp
+	// Scale is the ratio of image pixels to
+	// dps. If Scale is zero Image falls back to
+	// a scale that match a standard 72 DPI.
+	Scale float32
+}
+
+func (im Image) Layout(gtx *layout.Context) {
+	scale := im.Scale
+	if scale == 0 {
+		scale = 160.0 / 72.0
+	}
+	size := im.Src.Rect.Size()
+	wf, hf := float32(size.X), float32(size.Y)
+	w, h := gtx.Px(unit.Dp(wf*scale)), gtx.Px(unit.Dp(hf*scale))
+	cs := gtx.Constraints
+	d := image.Point{X: cs.Width.Constrain(w), Y: cs.Height.Constrain(h)}
+	var s op.StackOp
+	s.Push(gtx.Ops)
+	clip.Rect{Rect: f32.Rectangle{Max: toPointF(d)}}.Op(gtx.Ops).Add(gtx.Ops)
+	im.Src.Add(gtx.Ops)
+	paint.PaintOp{Rect: f32.Rectangle{Max: f32.Point{X: float32(w), Y: float32(h)}}}.Add(gtx.Ops)
+	s.Pop()
+	gtx.Dimensions = layout.Dimensions{Size: d}
+}
+
+func toPointF(p image.Point) f32.Point {
+	return f32.Point{X: float32(p.X), Y: float32(p.Y)}
+}