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/icon.go

@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package widget
+
+import (
+	"image"
+	"image/color"
+	"image/draw"
+
+	"gioui.org/f32"
+	"gioui.org/layout"
+	"gioui.org/op/paint"
+	"gioui.org/unit"
+	"golang.org/x/exp/shiny/iconvg"
+)
+
+type Icon struct {
+	Color color.RGBA
+	src   []byte
+	// Cached values.
+	op       paint.ImageOp
+	imgSize  int
+	imgColor color.RGBA
+}
+
+// NewIcon returns a new Icon from IconVG data.
+func NewIcon(data []byte) (*Icon, error) {
+	_, err := iconvg.DecodeMetadata(data)
+	if err != nil {
+		return nil, err
+	}
+	return &Icon{src: data, Color: color.RGBA{A: 0xff}}, nil
+}
+
+func (ic *Icon) Layout(gtx *layout.Context, sz unit.Value) {
+	ico := ic.image(gtx.Px(sz))
+	ico.Add(gtx.Ops)
+	paint.PaintOp{
+		Rect: f32.Rectangle{
+			Max: toPointF(ico.Size()),
+		},
+	}.Add(gtx.Ops)
+	gtx.Dimensions = layout.Dimensions{
+		Size: ico.Size(),
+	}
+}
+
+func (ic *Icon) image(sz int) paint.ImageOp {
+	if sz == ic.imgSize && ic.Color == ic.imgColor {
+		return ic.op
+	}
+	m, _ := iconvg.DecodeMetadata(ic.src)
+	dx, dy := m.ViewBox.AspectRatio()
+	img := image.NewRGBA(image.Rectangle{Max: image.Point{X: sz, Y: int(float32(sz) * dy / dx)}})
+	var ico iconvg.Rasterizer
+	ico.SetDstImage(img, img.Bounds(), draw.Src)
+	m.Palette[0] = ic.Color
+	iconvg.Decode(&ico, ic.src, &iconvg.DecodeOptions{
+		Palette: &m.Palette,
+	})
+	ic.op = paint.NewImageOp(img)
+	ic.imgSize = sz
+	ic.imgColor = ic.Color
+	return ic.op
+}