1 files changed, 109 insertions, 14 deletions

diff --git a/tui/layout.go b/tui/layout.go
index 1b3c3ed..210924f 100644
--- a/tui/layout.go
+++ b/tui/layout.go
@@ -7,12 +7,13 @@ import (
 )
 
 type Box struct {
+	id string
 	Width, Height BoxSize
 	Dir Direction
 	Overflow bool
-	Scroll int
 	Style *Style
 	Margins [4]int
+	Scroll *ScrollState
 	text []textRun
 	computedLines [][]textRun
 	children []*Box
@@ -68,10 +69,29 @@ type rect struct {
 	max [2]int
 }
 
-type BoxEvent struct {
+type ScrollState struct {
+	at string
+	offset int
+	absolute int
+	atFirst bool
+	atLast bool
 }
 
-type TextEvent struct {
+func (s *ScrollState) ToStart() {
+	*s = ScrollState {}
+}
+
+func (s *ScrollState) AtFirst() bool {
+	return s.atFirst
+}
+
+func (s *ScrollState) AtLast() bool {
+	return s.atLast
+}
+
+func (s *ScrollState) Scroll(amnt int) {
+	s.offset += amnt
+	s.absolute += amnt
 }
 
 var layout struct {
@@ -89,23 +109,22 @@ func top() *Box {
 	return layout.stack[len(layout.stack) - 1]
 }
 
-func Push(id string, box Box) BoxEvent {
+func Push(id string, box Box) {
 	if len(layout.stack) > 0 {
 		top().children = append(top().children, &box)
 	}
 	layout.stack = append(layout.stack, &box)
 	layout.front[id] = &box
+	box.id = id
 	for axis, value := range box.axes() {
 		if value >= 0 {
 			box.computedSize[axis] = int(value)
 		}
 	}
-	return BoxEvent {}
 }
 
-func Text(text string, style *Style) TextEvent {
+func Text(text string, style *Style) {
 	top().text = append(top().text, textRun {text, style})
-	return TextEvent {}
 }
 
 func Pop() {
@@ -292,12 +311,65 @@ func (b *Box) computePositions(axis int) {
 			if b.Dir.reverse() {
 				pos -= c.computedSize[axis]
 			}
+
 			c.computedPosition = pos
-			c.computedRect.min[axis] = b.computedRect.min[axis] + pos
-			c.computedRect.max[axis] = c.computedRect.min[axis] + c.computedSize[axis]
+
+			if b.Scroll != nil && b.Scroll.at != "" && b.Scroll.at == c.id {
+				p := c.computedPosition
+				if b.Dir.reverse() {
+					p = b.computedSize[axis] - p
+				}
+				b.Scroll.absolute = p
+				if !b.Dir.reverse() {
+					b.Scroll.absolute += b.Scroll.offset
+				} else {
+					b.Scroll.absolute += b.Scroll.offset
+				}
+			}
+
 			if !b.Dir.reverse() {
 				pos += c.computedSize[axis]
 			}
+		}
+		if b.Scroll != nil {
+			var first *Box
+			var last *Box
+			for _, c := range b.children {
+				if !b.Dir.reverse() {
+					c.computedPosition -= b.Scroll.absolute
+				} else {
+					c.computedPosition += b.Scroll.absolute
+				}
+				if c.computedPosition > b.computedRect.min[axis] &&
+						c.computedPosition < b.computedRect.max[axis] {
+					if first == nil {
+						first = c
+					}
+					last = c
+				}
+			}
+			if first == b.children[0] {
+				b.Scroll.atFirst = true
+			}
+			if last == b.children[len(b.children) - 1] {
+				b.Scroll.atLast = true
+			}
+			if first != nil {
+				p := first.computedPosition
+				if b.Dir.reverse() {
+					p = b.computedSize[axis] - p
+				}
+				b.Scroll.offset = -p
+				b.Scroll.at = first.id
+			}
+			if b.Scroll.absolute == 0 {
+				b.Scroll.at = ""
+				b.Scroll.offset = 0
+			}
+		}
+		for _, c := range b.children {
+			c.computedRect.min[axis] = b.computedRect.min[axis] + c.computedPosition
+			c.computedRect.max[axis] = c.computedRect.min[axis] + c.computedSize[axis]
 			c.computePositions(axis)
 		}
 	} else {
@@ -309,12 +381,22 @@ func (b *Box) computePositions(axis int) {
 	}
 }
 
-func (b *Box) drawComputed(parentStyle Style) {
+func (b *Box) drawComputed(parentRect rect, parentStyle Style) {
+	var viewRect rect = parentRect;
+	for i := 0; i < 2; i++ {
+		bMin := b.computedRect.min[i] + b.Margins[i * 2]
+		viewRect.min[i] = max(bMin, parentRect.min[i])
+	}
+	for i := 0; i < 2; i++ {
+		bMax := b.computedRect.max[i] - b.Margins[i * 2 + 1]
+		viewRect.max[i] = min(bMax, parentRect.max[i])
+	}
+
 	style := parentStyle
 	if b.Style != nil {
 		style = *b.Style
-		for y := b.computedRect.min[1]; y < b.computedRect.max[1]; y++ {
-			for x := b.computedRect.min[0]; x < b.computedRect.max[0]; x++ {
+		for y := viewRect.min[1]; y < viewRect.max[1]; y++ {
+			for x := viewRect.min[0]; x < viewRect.max[0]; x++ {
 				WriteAt(x, y, " ", style)
 			}
 		}
@@ -325,6 +407,15 @@ func (b *Box) drawComputed(parentStyle Style) {
 		if y > b.computedRect.max[1] - b.Margins[3] {
 			break
 		}
+		if y < b.computedRect.min[1] + b.Margins[2] {
+			continue
+		}
+		if y > parentRect.max[1] {
+			break
+		}
+		if y < parentRect.min[1] {
+			continue
+		}
 		for _, t := range l {
 			var s Style
 			if t.style != nil {
@@ -336,7 +427,7 @@ func (b *Box) drawComputed(parentStyle Style) {
 		}
 	}
 	for _, c := range b.children {
-		c.drawComputed(style)
+		c.drawComputed(viewRect, style)
 	}
 }
 
@@ -357,5 +448,9 @@ func DrawLayout() {
 		b.solve(axis)
 		b.computePositions(axis)
 	}
-	b.drawComputed(DefaultStyle)
+	var parentRect rect
+	size := Size()
+	parentRect.max = [2]int {size.Width, size.Height}
+	b.computedRect = parentRect
+	b.drawComputed(parentRect, DefaultStyle)
 }