From 664ce5f5560f3eb4efd2a59856d7d7338eb957b4 Mon Sep 17 00:00:00 2001
From: Sasha Koshka <sashakoshka@tebibyte.media>
Date: Mon, 13 May 2024 17:43:26 -0400
Subject: [PATCH] Add scroll code for ContainerBox

---
 containerbox.go | 75 +++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 63 insertions(+), 12 deletions(-)

diff --git a/containerbox.go b/containerbox.go
index 377361d..5a9899d 100644
--- a/containerbox.go
+++ b/containerbox.go
@@ -59,7 +59,7 @@ func (this *containerBox) ContentBounds () image.Rectangle {
 }
 
 func (this *containerBox) ScrollTo (point image.Point) {
-	// TODO: constrain scroll
+	if this.scroll == point { return }
 	this.scroll = point
 	this.invalidateLayout()
 }
@@ -68,19 +68,19 @@ func (this *containerBox) OnContentBoundsChange (callback func()) event.Cookie {
 	return this.on.contentBoundsChange.Connect(callback)
 }
 
-func (this *containerBox)  CaptureDND (capture bool) {
+func (this *containerBox) CaptureDND (capture bool) {
 	this.capture[eventCategoryDND] = capture
 }
 
-func (this *containerBox)  CaptureMouse (capture bool) {
+func (this *containerBox) CaptureMouse (capture bool) {
 	this.capture[eventCategoryMouse] = capture
 }
 
-func (this *containerBox)  CaptureScroll (capture bool) {
+func (this *containerBox) CaptureScroll (capture bool) {
 	this.capture[eventCategoryScroll] = capture
 }
 
-func (this *containerBox)  CaptureKeyboard (capture bool) {
+func (this *containerBox) CaptureKeyboard (capture bool) {
 	this.capture[eventCategoryKeyboard] = capture
 }
 
@@ -225,10 +225,14 @@ func (this *containerBox) notifyMinimumSizeChange (child anyBox) {
 	}
 }
 
+func (this *containerBox) boundedLayoutHints () tomo.LayoutHints {
+	hints := this.layoutHints()
+	hints.Bounds = this.ContentBounds().Add(this.InnerBounds().Min)
+	return hints
+}
+
 func (this *containerBox) layoutHints () tomo.LayoutHints {
-	innerBounds := this.InnerBounds().Sub(this.scroll)
 	return tomo.LayoutHints {
-		Bounds:    innerBounds,
 		OverflowX: this.hOverflow,
 		OverflowY: this.vOverflow,
 		AlignX:    this.hAlign,
@@ -240,10 +244,12 @@ func (this *containerBox) layoutHints () tomo.LayoutHints {
 func (this *containerBox) contentMinimum () image.Point {
 	minimum := this.box.contentMinimum()
 	if this.layout != nil {
-		minimum = minimum.Add (
-			this.layout.MinimumSize (
-				this.layoutHints(),
-				this.children))
+		layoutMinimum := this.layout.MinimumSize (
+			this.boundedLayoutHints(),
+			this.children)
+		if this.hOverflow { layoutMinimum.X = 0 }
+		if this.vOverflow { layoutMinimum.Y = 0 }
+		minimum = minimum.Add(layoutMinimum)
 	}
 	return minimum
 }
@@ -251,14 +257,59 @@ func (this *containerBox) contentMinimum () image.Point {
 func (this *containerBox) doLayout () {
 	this.box.doLayout()
 	previousContentBounds := this.contentBounds
+
+	// by default, use innerBounds for contentBounds. if a direction
+	// overflows, use the layout's minimum size for it.
+	var minimum image.Point
 	if this.layout != nil {
-		this.layout.Arrange(this.layoutHints(), this.children)
+		minimum = this.layout.MinimumSize (
+			this.layoutHints(),
+			this.children)
 	}
+	innerBounds := this.InnerBounds()
+	this.contentBounds = innerBounds
+	if this.hOverflow { this.contentBounds.Max.X = this.contentBounds.Min.X + minimum.X }
+	if this.vOverflow { this.contentBounds.Max.Y = this.contentBounds.Min.Y + minimum.Y }
+
+	// offset the content bounds by the scroll so children can be positioned
+	// accordingly.
+	this.constrainScroll()
+	this.contentBounds = this.contentBounds.Sub(this.scroll).Sub(innerBounds.Min)
+	
+	// arrange children
+	if this.layout != nil {
+		this.layout.Arrange(this.boundedLayoutHints(), this.children)
+	}
+	
 	if previousContentBounds != this.contentBounds {
 		this.on.contentBoundsChange.Broadcast()
 	}
 }
 
+func (this *containerBox) constrainScroll () {
+	innerBounds := this.InnerBounds()
+	width  := this.contentBounds.Dx()
+	height := this.contentBounds.Dy()
+
+	// X
+	if width <= innerBounds.Dx() {
+		this.scroll.X = 0
+	} else if this.scroll.X < 0 {
+		this.scroll.X = 0
+	} else if this.scroll.X > width - innerBounds.Dx() {
+		this.scroll.X = width - innerBounds.Dx()
+	}
+
+	// Y
+	if height <= innerBounds.Dy() {
+		this.scroll.Y = 0
+	} else if this.scroll.Y < 0 {
+		this.scroll.Y = 0
+	} else if this.scroll.Y > height - innerBounds.Dy() {
+		this.scroll.Y = height - innerBounds.Dy()
+	}
+}
+
 func (this *containerBox) recursiveRedo () {
 	this.doLayout()
 	this.doDraw()