1 files changed, 132 insertions, 0 deletions
diff --git a/gui/layout/scroller.go b/gui/layout/scroller.go
new file mode 100644
index 0000000..b7fc3f5
--- /dev/null
+++ b/gui/layout/scroller.go
@@ -0,0 +1,132 @@
+package layout
+
+import (
+	"image"
+	"image/color"
+	"image/draw"
+	"sync"
+
+	"volute/gui"
+	"volute/gui/win"
+)
+
+var _ Layout = &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) Intercept(env gui.Env) gui.Env {
+	evs := env.Events()
+	out, in := gui.MakeEventsChan()
+	drawChan := make(chan func(draw.Image) image.Rectangle)
+	ret := &muxEnv{out, drawChan}
+	var lastResize gui.Resize
+	var img draw.Image
+	img = image.NewRGBA(image.ZR)
+	var mu sync.Mutex
+	var over bool
+
+	go func() {
+		for dc := range drawChan {
+			mu.Lock()
+			// draw.Draw will not draw out of bounds, call should be inexpensive if element not visible
+			res := dc(img)
+			// Only send a draw call up if visibly changed
+			if res.Intersect(img.Bounds()) != image.ZR {
+				env.Draw() <- func(drw draw.Image) image.Rectangle {
+					draw.Draw(drw, lastResize.Rectangle, img, lastResize.Rectangle.Min, draw.Over)
+					return img.Bounds()
+				}
+			}
+			mu.Unlock()
+		}
+	}()
+
+	go func() {
+		for ev := range evs {
+			switch ev := ev.(type) {
+			case win.MoMove:
+				mu.Lock()
+				over = ev.Point.In(lastResize.Rectangle)
+				mu.Unlock()
+			case win.MoScroll:
+				if !over {
+					continue
+				}
+				mu.Lock()
+				oldoff := s.Offset
+				v := s.Length*s.ChildHeight + ((s.Length + 1) * s.Gap)
+				if s.Vertical {
+					h := lastResize.Dx()
+					s.Offset = clamp(s.Offset+ev.Point.X*16, h-v, 0)
+				} else {
+					h := lastResize.Dy()
+					s.Offset = clamp(s.Offset+ev.Point.Y*16, h-v, 0)
+				}
+				if oldoff != s.Offset {
+					s.redraw(img, img.Bounds())
+					in <- lastResize
+				}
+				mu.Unlock()
+			case gui.Resize:
+				mu.Lock()
+				lastResize = ev
+				img = image.NewRGBA(lastResize.Rectangle)
+				s.redraw(img, img.Bounds())
+				mu.Unlock()
+				in <- ev
+			default:
+				in <- ev
+			}
+		}
+	}()
+	return ret
+}
+
+func (s Scroller) Lay(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
+}