From 7d4ddaf387f98a6c57697aea6cad1d309e5d8761 Mon Sep 17 00:00:00 2001
From: Sasha Koshka <sashakoshka@tebibyte.media>
Date: Sun, 16 Apr 2023 14:12:55 -0400
Subject: [PATCH] Scrolling over a ScrollContainer will now scroll it

---
 backends/x/entity.go          | 15 +++++++++++++++
 backends/x/event.go           | 20 +++++++++++---------
 backends/x/system.go          |  5 +++++
 elements/containers/scroll.go | 18 ++++++++++++++++++
 4 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/backends/x/entity.go b/backends/x/entity.go
index c15a797..bc9c7b0 100644
--- a/backends/x/entity.go
+++ b/backends/x/entity.go
@@ -81,6 +81,21 @@ func (entity *entity) childAt (point image.Point) *entity {
 	return entity
 }
 
+func (entity *entity) scrollTargetChildAt (point image.Point) *entity {
+	for _, child := range entity.children {
+		if point.In(child.bounds) {
+			result := child.scrollTargetChildAt(point)
+			if result != nil { return result }
+			break
+		}
+	}
+
+	if _, ok := entity.element.(tomo.ScrollTarget); ok {
+		return entity
+	}
+	return nil
+}
+
 // ----------- Entity ----------- //
 
 func (entity *entity) Invalidate () {
diff --git a/backends/x/event.go b/backends/x/event.go
index 73ea3c1..2f573ba 100644
--- a/backends/x/event.go
+++ b/backends/x/event.go
@@ -190,20 +190,22 @@ func (window *window) handleButtonPress (
 	insideWindow := point.In(window.canvas.Bounds())
 	scrolling    := buttonEvent.Detail >= 4 && buttonEvent.Detail <= 7
 
-	underneath := window.system.childAt(point)
-	
 	if !insideWindow && window.shy && !scrolling {
 		window.Close()
 	} else if scrolling {
-		if child, ok := underneath.element.(tomo.ScrollTarget); ok {
-			sum := scrollSum { }
-			sum.add(buttonEvent.Detail, window, buttonEvent.State)
-			window.compressScrollSum(buttonEvent, &sum)
-			child.HandleScroll (
-				point.X, point.Y,
-				float64(sum.x), float64(sum.y))
+		underneath := window.system.scrollTargetChildAt(point)
+		if underneath != nil {
+			if child, ok := underneath.element.(tomo.ScrollTarget); ok {
+				sum := scrollSum { }
+				sum.add(buttonEvent.Detail, window, buttonEvent.State)
+				window.compressScrollSum(buttonEvent, &sum)
+				child.HandleScroll (
+					point.X, point.Y,
+					float64(sum.x), float64(sum.y))
+			}
 		}
 	} else {
+		underneath := window.system.childAt(point)
 		if child, ok := underneath.element.(tomo.MouseTarget); ok {
 			window.system.drags[buttonEvent.Detail] = child
 			child.HandleMouseDown (
diff --git a/backends/x/system.go b/backends/x/system.go
index 84ffa23..78a43b7 100644
--- a/backends/x/system.go
+++ b/backends/x/system.go
@@ -123,6 +123,11 @@ func (system *system) childAt (point image.Point) *entity {
 	return system.child.childAt(point)
 }
 
+func (system *system) scrollTargetChildAt (point image.Point) *entity {
+	if system.child == nil { return nil }
+	return system.child.scrollTargetChildAt(point)
+}
+
 func (system *system) resizeChildToFit () {
 	system.child.bounds        = system.canvas.Bounds()
 	system.child.clippedBounds = system.child.bounds
diff --git a/elements/containers/scroll.go b/elements/containers/scroll.go
index 5c420c4..b83fc47 100644
--- a/elements/containers/scroll.go
+++ b/elements/containers/scroll.go
@@ -148,6 +148,16 @@ func (element *Scroll) HandleChildScrollBoundsChange (tomo.Scrollable) {
 	}
 }
 
+func (element *Scroll) HandleScroll (
+	x, y int,
+	deltaX, deltaY float64,
+) {
+	horizontal, vertical := element.child.ScrollAxes()
+	if !horizontal { deltaX = 0 }
+	if !vertical   { deltaY = 0 }
+	element.scrollChildBy(int(deltaX), int(deltaY))
+}
+
 func (element *Scroll) SetTheme (theme tomo.Theme) {
 	if theme == element.theme.Theme { return }
 	element.theme.Theme = theme
@@ -195,3 +205,11 @@ func (element *Scroll) updateEnabled () {
 		element.vertical.SetEnabled(vertical)
 	}
 }
+
+func (element *Scroll) scrollChildBy (x, y int) {
+	if element.child == nil { return }
+	scrollPoint :=
+		element.child.ScrollViewportBounds().Min.
+		Add(image.Pt(x, y))
+	element.child.ScrollTo(scrollPoint)
+}