From fe5878bc63fd41c40c202e8eff087bc3a37d50ef Mon Sep 17 00:00:00 2001
From: Chris Waldon <christopher.waldon.dev@gmail.com>
Date: Mon, 19 Dec 2022 10:09:00 -0500
Subject: [PATCH] widget: track minWidth of editor for alignment

This commit extends the editor to keep track of its own minimum constraint
and to provide that value to the text shaper for the purpose of aligning
text. Without this, the shaper does not know how much of the width of the
editor to use for alignment purposes.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>
---
 widget/editor.go      | 37 ++++++++++++++++-------------
 widget/editor_test.go | 54 +++++++++++++++++++++++++++----------------
 2 files changed, 55 insertions(+), 36 deletions(-)

diff --git a/widget/editor.go b/widget/editor.go
index e8e7d7a6..9ae07d7b 100644
--- a/widget/editor.go
+++ b/widget/editor.go
@@ -52,21 +52,21 @@ type Editor struct {
 	// all characters are allowed.
 	Filter string
 
-	eventKey     int
-	font         text.Font
-	shaper       *text.Shaper
-	textSize     fixed.Int26_6
-	blinkStart   time.Time
-	focused      bool
-	rr           editBuffer
-	maskReader   maskReader
-	lastMask     rune
-	maxWidth     int
-	viewSize     image.Point
-	valid        bool
-	regions      []region
-	dims         layout.Dimensions
-	requestFocus bool
+	eventKey           int
+	font               text.Font
+	shaper             *text.Shaper
+	textSize           fixed.Int26_6
+	blinkStart         time.Time
+	focused            bool
+	rr                 editBuffer
+	maskReader         maskReader
+	lastMask           rune
+	maxWidth, minWidth int
+	viewSize           image.Point
+	valid              bool
+	regions            []region
+	dims               layout.Dimensions
+	requestFocus       bool
 
 	// offIndex is an index of rune index to byte offsets.
 	offIndex []offEntry
@@ -547,10 +547,15 @@ func (e *Editor) Layout(gtx layout.Context, lt *text.Shaper, font text.Font, siz
 	if e.SingleLine {
 		maxWidth = math.MaxInt
 	}
+	minWidth := gtx.Constraints.Min.X
 	if maxWidth != e.maxWidth {
 		e.maxWidth = maxWidth
 		e.invalidate()
 	}
+	if minWidth != e.minWidth {
+		e.minWidth = minWidth
+		e.invalidate()
+	}
 	if lt != e.shaper {
 		e.shaper = lt
 		e.invalidate()
@@ -891,7 +896,7 @@ func (e *Editor) layoutText(lt *text.Shaper) {
 			Font:      e.font,
 			PxPerEm:   e.textSize,
 			Alignment: e.Alignment,
-		}, 0, e.maxWidth, e.locale, r)
+		}, e.minWidth, e.maxWidth, e.locale, r)
 		for glyph, ok := it.processGlyph(lt.NextGlyph()); ok; glyph, ok = it.processGlyph(lt.NextGlyph()) {
 			e.index.Glyph(glyph)
 		}
diff --git a/widget/editor_test.go b/widget/editor_test.go
index d82a4355..703e2e5a 100644
--- a/widget/editor_test.go
+++ b/widget/editor_test.go
@@ -115,7 +115,7 @@ func TestEditorZeroDimensions(t *testing.T) {
 func TestEditorConfigurations(t *testing.T) {
 	gtx := layout.Context{
 		Ops:         new(op.Ops),
-		Constraints: layout.Exact(image.Pt(100, 100)),
+		Constraints: layout.Exact(image.Pt(300, 300)),
 		Locale:      english,
 	}
 	cache := text.NewShaper(gofont.Collection())
@@ -126,27 +126,41 @@ func TestEditorConfigurations(t *testing.T) {
 
 	// Ensure that both ends of the text are reachable in all permutations
 	// of settings that influence layout.
-	for _, lineMode := range []bool{true, false} {
+	for _, singleLine := range []bool{true, false} {
 		for _, alignment := range []text.Alignment{text.Start, text.Middle, text.End} {
-			t.Run(fmt.Sprintf("SingleLine: %v Alignment: %v", lineMode, alignment), func(t *testing.T) {
-				defer func() {
-					if err := recover(); err != nil {
-						t.Error(err)
+			for _, zeroMin := range []bool{true, false} {
+				t.Run(fmt.Sprintf("SingleLine: %v Alignment: %v ZeroMinConstraint: %v", singleLine, alignment, zeroMin), func(t *testing.T) {
+					defer func() {
+						if err := recover(); err != nil {
+							t.Error(err)
+						}
+					}()
+					if zeroMin {
+						gtx.Constraints.Min = image.Point{}
+					} else {
+						gtx.Constraints.Min = gtx.Constraints.Max
 					}
-				}()
-				e := new(Editor)
-				e.SingleLine = lineMode
-				e.Alignment = alignment
-				e.SetText(sentence)
-				e.SetCaret(0, 0)
-				e.Layout(gtx, cache, font, fontSize, nil)
-				e.SetCaret(runes, runes)
-				e.Layout(gtx, cache, font, fontSize, nil)
-				coords := e.CaretCoords()
-				if int(coords.X) > gtx.Constraints.Max.X || int(coords.Y) > gtx.Constraints.Max.Y {
-					t.Errorf("caret coordinates %v exceed constraints %v", coords, gtx.Constraints.Max)
-				}
-			})
+					e := new(Editor)
+					e.SingleLine = singleLine
+					e.Alignment = alignment
+					e.SetText(sentence)
+					e.SetCaret(0, 0)
+					dims := e.Layout(gtx, cache, font, fontSize, nil)
+					if dims.Size.X < gtx.Constraints.Min.X || dims.Size.Y < gtx.Constraints.Min.Y {
+						t.Errorf("expected min size %#+v, got %#+v", gtx.Constraints.Min, dims.Size)
+					}
+					coords := e.CaretCoords()
+					if halfway := float32(gtx.Constraints.Min.X) * .5; !singleLine && alignment == text.Middle && !zeroMin && coords.X != halfway {
+						t.Errorf("expected caret X to be %f, got %f", halfway, coords.X)
+					}
+					e.SetCaret(runes, runes)
+					e.Layout(gtx, cache, font, fontSize, nil)
+					coords = e.CaretCoords()
+					if int(coords.X) > gtx.Constraints.Max.X || int(coords.Y) > gtx.Constraints.Max.Y {
+						t.Errorf("caret coordinates %v exceed constraints %v", coords, gtx.Constraints.Max)
+					}
+				})
+			}
 		}
 	}
 }