1 files changed, 121 insertions, 0 deletions
diff --git a/layout/rows.go b/layout/rows.go
new file mode 100644
index 0000000..3912878
--- /dev/null
+++ b/layout/rows.go
@@ -0,0 +1,121 @@
+package layout
+
+import (
+	"image"
+	"image/draw"
+
+	"github.com/faiface/gui"
+)
+
+// NewRows creates layout with nrows children arranged in rows.
+// It returns a slice containing an Env for each row.
+// The height of each row is determined by the draw calls received from that row.
+func NewRows(env gui.Env, nrows uint, o ...Option) []gui.Env {
+	opts := evalOptions(o...)
+
+	// Create event and draw channels for each row
+	eventss := make([]chan gui.Event, nrows)                       // to children
+	drawss := make([]chan func(draw.Image) image.Rectangle, nrows) // from children
+	var i uint
+	for i = 0; i < nrows; i++ {
+		eventss[i] = make(chan gui.Event)
+		drawss[i] = make(chan func(draw.Image) image.Rectangle)
+	}
+
+	go func() {
+		defer close(env.Draw())
+		defer closeAll(eventss)
+
+		resize := func(area image.Rectangle, rowHeights []uint) {
+			// Redraw background
+			env.Draw() <- drawSubImage(drawBackground(opts.bg), area)
+
+			// Send resize events to rows
+			off := area.Min // vertical offset from parent area origin
+			var i uint
+			for i = 0; i < nrows; i++ {
+				eventss[i] <- gui.Resize{image.Rectangle{
+					off,
+					off.Add(image.Pt(area.Dx(), int(rowHeights[i])))}}
+				off.Y += int(rowHeights[i])
+			}
+		}
+
+		// Receive and send first Resize event
+		event := (<-env.Events()).(gui.Resize) // first event guaranteed to be Resize
+		area := event.Rectangle
+		rowHeights := make([]uint, nrows) // initially zero until draw call received
+		resize(area, rowHeights)          // send first Resize to children
+
+		// Multiplex rows' draw channels. Tag draw functions with row index.
+		draws := make(chan taggedDrawCall)
+		wg := newWaitGroup(nrows) // done when all rows close their Draw channel
+		var i uint
+		for i = 0; i < nrows; i++ {
+			go muxDrawCalls(drawss[i], i, draws, wg)
+		}
+		defer close(draws)
+
+		for {
+			select {
+			case event := <-env.Events(): // event from parent
+				switch event := event.(type) {
+				case gui.Resize:
+					area = event.Rectangle
+					resize(area, rowHeights)
+				default:
+					multicast(event, eventss) // forward event to all rows
+				}
+			case drw := <-draws: // draw call from a row
+				rh := rowHeight(area, drw.f)
+				oldrh := rowHeights[drw.idx]
+				rowHeights[drw.idx] = rh
+				if rh != oldrh { // size changed; redraw all rows
+					go resize(area, rowHeights)
+				} else { // Same size; just redraw the one row
+					env.Draw() <- drawSubImage(drw.f, rowArea(area, rowHeights, drw.idx))
+				}
+			case <-wg.Wait(): // all rows' draw channels closed
+				return
+			}
+		}
+	}()
+
+	// Create and return row Envs
+	rows := make([]gui.Env, nrows)
+	for i := range rows {
+		rows[i] = rowEnv{eventss[i], drawss[i]}
+	}
+	return rows
+}
+
+// RowHeight calculates the height of a row within the area of the layout
+// using a draw function received from the row.
+func rowHeight(area image.Rectangle, drw func(draw.Image) image.Rectangle) uint {
+	img := image.NewAlpha(area)
+	return uint(drw(img).Canon().Dy())
+}
+
+// RowArea returns the drawing area of row i within the area of the layout.
+func rowArea(area image.Rectangle, rowHeights []uint, i uint) image.Rectangle {
+	min := area.Min.Add(image.Pt(0, int(sum(rowHeights[:i]))))
+	max := min.Add(image.Pt(area.Dx(), int(rowHeights[i])))
+	return image.Rectangle{min, max}
+}
+
+type rowEnv struct {
+	events <-chan gui.Event
+	draw   chan<- func(draw.Image) image.Rectangle
+}
+
+// Events implements the Env interface.
+func (r rowEnv) Events() <-chan gui.Event { return r.events }
+
+// Draw implements the Env interface.
+func (r rowEnv) Draw() chan<- func(draw.Image) image.Rectangle { return r.draw }
+
+func closeAll[T any](cs []chan T) {
+	for _, c := range cs {
+		close(c)
+	}
+}