widget/material: add hover to Button

Signed-off-by: Egon Elbre <egonelbre@gmail.com>

internal/f32color/rgba.go

@@ -172,6 +172,17 @@ func Disabled(c color.NRGBA) (d color.NRGBA) {
 	}
 }
 
+// Hovered blends color towards a brighter color.
+func Hovered(c color.NRGBA) (d color.NRGBA) {
+	const r = 0x20 // lighten ratio
+	return color.NRGBA{
+		R: byte(255 - int(255-c.R)*(255-r)/256),
+		G: byte(255 - int(255-c.G)*(255-r)/256),
+		B: byte(255 - int(255-c.B)*(255-r)/256),
+		A: c.A,
+	}
+}
+
 // approxLuminance is a fast approximate version of RGBA.Luminance.
 func approxLuminance(c color.NRGBA) byte {
 	const (

widget/material/button.go

@@ -128,8 +128,11 @@ func (b ButtonLayoutStyle) Layout(gtx layout.Context, w layout.Widget) layout.Di
 				Y: float32(gtx.Constraints.Min.Y),
 			}}, rr).Add(gtx.Ops)
 			background := b.Background
-			if gtx.Queue == nil {
+			switch {
+			case gtx.Queue == nil:
 				background = f32color.Disabled(b.Background)
+			case b.Button.Hovered():
+				background = f32color.Hovered(b.Background)
 			}
 			paint.Fill(gtx.Ops, background)
 			for _, c := range b.Button.History() {
@@ -155,8 +158,11 @@ func (b IconButtonStyle) Layout(gtx layout.Context) layout.Dimensions {
 				Max: f32.Point{X: sizexf, Y: sizeyf},
 			}, rr).Add(gtx.Ops)
 			background := b.Background
-			if gtx.Queue == nil {
+			switch {
+			case gtx.Queue == nil:
 				background = f32color.Disabled(b.Background)
+			case b.Button.Hovered():
+				background = f32color.Hovered(b.Background)
 			}
 			paint.Fill(gtx.Ops, background)
 			for _, c := range b.Button.History() {