From 22aa00f4767a62091329bbce1e67410136a0c19b Mon Sep 17 00:00:00 2001
From: Gordon Klaus <gordon.klaus@gmail.com>
Date: Thu, 19 Jan 2023 11:37:11 +0100
Subject: [PATCH] widget/material: add Float.Invert

Setting Float.Invert=true not only inverts the order of values (which was already easily done by swapping min and max), it also draws the widget inverted so that the track is darkened on the opposite side from usual.

This patch also fixes a bug wherein a vertical slider was drawn inverted by default.

Signed-off-by: Gordon Klaus <gordon.klaus@gmail.com>
---
 widget/float.go           | 10 +++++++---
 widget/material/slider.go | 36 +++++++++++++++++++++++-------------
 2 files changed, 30 insertions(+), 16 deletions(-)

diff --git a/widget/float.go b/widget/float.go
index 01f13a71..1581e7de 100644
--- a/widget/float.go
+++ b/widget/float.go
@@ -13,8 +13,9 @@ import (
 
 // Float is for selecting a value in a range.
 type Float struct {
-	Value float32
-	Axis  layout.Axis
+	Value  float32
+	Axis   layout.Axis
+	Invert bool
 
 	drag    gesture.Drag
 	pos     float32 // position normalized to [0, 1]
@@ -43,7 +44,10 @@ func (f *Float) Layout(gtx layout.Context, pointerMargin int, min, max float32)
 	if de != nil {
 		xy := de.Position.X
 		if f.Axis == layout.Vertical {
-			xy = de.Position.Y
+			xy = f.length - de.Position.Y
+		}
+		if f.Invert {
+			xy = f.length - xy
 		}
 		f.pos = xy / f.length
 		value = min + (max-min)*f.pos
diff --git a/widget/material/slider.go b/widget/material/slider.go
index 9c02be90..d05d2dd9 100644
--- a/widget/material/slider.go
+++ b/widget/material/slider.go
@@ -61,26 +61,36 @@ func (s SliderStyle) Layout(gtx layout.Context) layout.Dimensions {
 		color = f32color.Disabled(color)
 	}
 
-	// Draw track before thumb.
-	track := image.Rectangle{
-		Min: axis.Convert(image.Pt(thumbRadius, sizeCross/2-trackWidth/2)),
-		Max: axis.Convert(image.Pt(thumbPos, sizeCross/2+trackWidth/2)),
+	rect := func(minx, miny, maxx, maxy int) image.Rectangle {
+		r := image.Rect(minx, miny, maxx, maxy)
+		if s.Float.Invert != (axis == layout.Vertical) {
+			r.Max.X, r.Min.X = sizeMain-r.Min.X, sizeMain-r.Max.X
+		}
+		r.Min = axis.Convert(r.Min)
+		r.Max = axis.Convert(r.Max)
+		return r
 	}
+
+	// Draw track before thumb.
+	track := rect(
+		thumbRadius, sizeCross/2-trackWidth/2,
+		thumbPos, sizeCross/2+trackWidth/2,
+	)
 	paint.FillShape(gtx.Ops, color, clip.Rect(track).Op())
 
 	// Draw track after thumb.
-	track = image.Rectangle{
-		Min: axis.Convert(image.Pt(thumbPos, axis.Convert(track.Min).Y)),
-		Max: axis.Convert(image.Pt(sizeMain-thumbRadius, axis.Convert(track.Max).Y)),
-	}
+	track = rect(
+		thumbPos, axis.Convert(track.Min).Y,
+		sizeMain-thumbRadius, axis.Convert(track.Max).Y,
+	)
 	paint.FillShape(gtx.Ops, f32color.MulAlpha(color, 96), clip.Rect(track).Op())
 
 	// Draw thumb.
-	pt := axis.Convert(image.Pt(thumbPos, sizeCross/2))
-	thumb := image.Rectangle{
-		Min: image.Pt(pt.X-thumbRadius, pt.Y-thumbRadius),
-		Max: image.Pt(pt.X+thumbRadius, pt.Y+thumbRadius),
-	}
+	pt := image.Pt(thumbPos, sizeCross/2)
+	thumb := rect(
+		pt.X-thumbRadius, pt.Y-thumbRadius,
+		pt.X+thumbRadius, pt.Y+thumbRadius,
+	)
 	paint.FillShape(gtx.Ops, color, clip.Ellipse(thumb).Op(gtx.Ops))
 
 	return layout.Dimensions{Size: size}