1 files changed, 127 insertions, 0 deletions
diff --git a/scroller.go b/scroller.go
new file mode 100644
index 0000000..fe411f3
--- /dev/null
+++ b/scroller.go
@@ -0,0 +1,127 @@
+package gui
+
+import (
+	"image"
+	"image/color"
+	"image/draw"
+
+	"git.samanthony.xyz/share"
+)
+
+var _ Scheme = Scroller{}
+
+type Scroller struct {
+	Background  color.Color
+	Length      int
+	ChildHeight int
+	Offset      int
+	Gap         int
+	Vertical    bool
+}
+
+func (s Scroller) redraw(drw draw.Image, bounds image.Rectangle) {
+	col := s.Background
+	if col == nil {
+		col = image.Black
+	}
+	draw.Draw(drw, bounds, image.NewUniform(col), image.ZP, draw.Src)
+}
+
+func clamp(val, a, b int) int {
+	if a > b {
+		if val < b {
+			return b
+		}
+		if val > a {
+			return a
+		}
+	} else {
+		if val > b {
+			return b
+		}
+		if val < a {
+			return a
+		}
+	}
+	return val
+}
+
+func (s Scroller) Partition(bounds image.Rectangle) []image.Rectangle {
+	items := s.Length
+	ch := s.ChildHeight
+	gap := s.Gap
+
+	ret := make([]image.Rectangle, items)
+	Y := bounds.Min.Y + s.Offset + gap
+	for i := 0; i < items; i++ {
+		r := image.Rect(bounds.Min.X+gap, Y, bounds.Max.X-gap, Y+ch)
+		ret[i] = r
+		Y += ch + gap
+	}
+	return ret
+}
+
+func (s Scroller) Intercept(parent Env) Env {
+	lastResize := share.NewVal[image.Rectangle]()
+	img := share.NewVal[draw.Image]()
+	mouseOver := share.NewVal[bool]()
+
+	lastResize.Set <- image.Rectangle{}
+	img.Set <- image.NewRGBA(image.Rectangle{})
+	mouseOver.Set <- false
+
+	return newEnv(parent,
+		func(event Event, events chan<- Event) {
+			switch event := event.(type) {
+			case MoMove:
+				mouseOver.Set <- event.Point.In(lastResize.Get())
+			case MoScroll:
+				if !mouseOver.Get() {
+					break
+				}
+
+				oldoff := s.Offset
+				v := s.Length*s.ChildHeight + ((s.Length + 1) * s.Gap)
+				bounds := lastResize.Get()
+
+				if s.Vertical {
+					h := bounds.Dx()
+					s.Offset = clamp(s.Offset+event.Point.X*16, h-v, 0)
+				} else {
+					h := bounds.Dy()
+					s.Offset = clamp(s.Offset+event.Point.Y*16, h-v, 0)
+				}
+
+				if oldoff != s.Offset {
+					m := img.Get()
+					s.redraw(m, m.Bounds())
+					events <- Resize{bounds}
+				}
+			case Resize:
+				lastResize.Set <- event.Rectangle
+
+				m := image.NewRGBA(event.Rectangle)
+				img.Set <- m
+				s.redraw(m, m.Bounds())
+
+				events <- event
+			default:
+				events <- event
+			}
+		},
+		func(drawFunc func(draw.Image) image.Rectangle, drawChan chan<- func(draw.Image) image.Rectangle) {
+			m := img.Get()
+			if drawFunc(m).Intersect(m.Bounds()) != image.ZR {
+				drawChan <- func(drw draw.Image) image.Rectangle {
+					bounds := lastResize.Get()
+					draw.Draw(drw, bounds, m, bounds.Min, draw.Over)
+					return m.Bounds()
+				}
+			}
+		},
+		func() {
+			lastResize.Close()
+			img.Close()
+			mouseOver.Close()
+		})
+}