From 8f28d1044fb83153fde4505421b75072930d6fb9 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Mon, 9 Feb 2026 22:00:33 -0500
Subject: layout: add background color option

---
 layout/doc.go     | 15 ---------------
 layout/layout.go  | 28 ++++++++++++++++++++++++++++
 layout/options.go | 34 ++++++++++++++++++++++++++++++++++
 layout/region.go  | 13 +++++++++----
 4 files changed, 71 insertions(+), 19 deletions(-)
 delete mode 100644 layout/doc.go
 create mode 100644 layout/layout.go
 create mode 100644 layout/options.go

(limited to 'layout')

diff --git a/layout/doc.go b/layout/doc.go
deleted file mode 100644
index bae4673..0000000
--- a/layout/doc.go
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
-Package layout provides means of partitioning screen space.
-
-A layout exists in a parent Env, and has one or more child Envs. It
-acts as a multiplexer for the children. The parent Env may be a window,
-another layout, or whatever... Several layers of layouts can be composed.
-
-A layout allocates screen area to its children by intercepting Resize
-events from the parent Env. Upon reception by the layout, a Resize event
-is transformed for each child, and forwarded to them.
-
-Draw calls from the children are intercepted and translated onto their
-respective areas before being forwarded to the parent Env.
-*/
-package layout
diff --git a/layout/layout.go b/layout/layout.go
new file mode 100644
index 0000000..b04aa35
--- /dev/null
+++ b/layout/layout.go
@@ -0,0 +1,28 @@
+/*
+Package layout provides means of partitioning screen space.
+
+A layout exists in a parent Env, and has one or more child Envs. It
+acts as a multiplexer for the children. The parent Env may be a window,
+another layout, or whatever... Several layers of layouts can be composed.
+
+A layout allocates screen area to its children by intercepting Resize
+events from the parent Env. Upon reception by the layout, a Resize event
+is transformed for each child, and forwarded to them.
+
+Draw calls from the children are intercepted and translated onto their
+respective areas before being forwarded to the parent Env.
+*/
+package layout
+
+import (
+	"image"
+	"image/color"
+	"image/draw"
+)
+
+func drawBackground(c color.Color) func(draw.Image) image.Rectangle {
+	return func(img draw.Image) image.Rectangle {
+		draw.Draw(img, img.Bounds(), &image.Uniform{c}, image.ZP, draw.Src)
+		return img.Bounds()
+	}
+}
diff --git a/layout/options.go b/layout/options.go
new file mode 100644
index 0000000..2ea0c81
--- /dev/null
+++ b/layout/options.go
@@ -0,0 +1,34 @@
+package layout
+
+import (
+	"image/color"
+)
+
+var (
+	defaultBg = color.Transparent
+)
+
+// Option is a function option for layout constructors.
+type Option func(*options)
+
+type options struct {
+	bg color.Color // background color
+}
+
+// Background sets the background color of a layout.
+func Background(bg color.Color) Option {
+	return func(o *options) {
+		o.bg = bg
+	}
+}
+
+// EvalOptions evaluates a list of option functions, returning the final set.
+func evalOptions(o ...Option) options {
+	opts := options{
+		bg: defaultBg,
+	}
+	for i := range o {
+		o[i](&opts)
+	}
+	return opts
+}
diff --git a/layout/region.go b/layout/region.go
index 1e92455..4e3a791 100644
--- a/layout/region.go
+++ b/layout/region.go
@@ -15,7 +15,9 @@ type Region struct {
 
 // NewRegion creates a region layout that occupies part of the parent env's area, as determined by the resize function.
 // Resize takes the area of the parent and returns the area of the region.
-func NewRegion(env gui.Env, resize func(image.Rectangle) image.Rectangle) gui.Env {
+func NewRegion(env gui.Env, resize func(image.Rectangle) image.Rectangle, o ...Option) gui.Env {
+	opts := evalOptions(o...)
+
 	events := make(chan gui.Event)                     // to child
 	drw := make(chan func(draw.Image) image.Rectangle) // from child
 
@@ -25,17 +27,20 @@ func NewRegion(env gui.Env, resize func(image.Rectangle) image.Rectangle) gui.En
 		area := resize(event.(gui.Resize).Rectangle) // first event guaranteed to be Resize
 		events <- gui.Resize{area}
 
+		env.Draw() <- drawBackground(opts.bg)
+
 		for {
 			select {
-			case event := <-env.Events():
+			case event := <-env.Events(): // event from parent
 				switch event := event.(type) {
 				case gui.Resize:
+					env.Draw() <- drawBackground(opts.bg)
 					area = resize(event.Rectangle)
-					events <- gui.Resize{area}
+					events <- gui.Resize{area} // forward to child
 				default:
 					events <- event
 				}
-			case f, ok := <-drw:
+			case f, ok := <-drw: // draw call from child
 				if !ok {
 					close(events)
 					close(env.Draw())
-- 
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