1 files changed, 97 insertions, 0 deletions
diff --git a/layout/geo.go b/layout/geo.go
new file mode 100644
index 0000000..6f84049
--- /dev/null
+++ b/layout/geo.go
@@ -0,0 +1,97 @@
+package layout
+
+import (
+	"fmt"
+	"image"
+)
+
+// ResizeFunc is a function that computes the area of a layout when it receives a Resize event.
+// It takes the Resize's Rectangle and returns the area that the layout should cover.
+type ResizeFunc func(image.Rectangle) image.Rectangle
+
+// Full resizes a layout to consume all of its parent's area.
+func Full() ResizeFunc {
+	return func(r image.Rectangle) image.Rectangle { return r }
+}
+
+// Quad1 resizes a layout to consume the top-right quadrant of its parent.
+func Quad1() ResizeFunc {
+	return func(r image.Rectangle) image.Rectangle {
+		mid := midpoint(r)
+		return image.Rect(mid.X, r.Min.Y, r.Max.X, mid.Y)
+	}
+}
+
+// Quad2 resizes a layout to consume the top-left quadrant of its parent.
+func Quad2() ResizeFunc {
+	return func(r image.Rectangle) image.Rectangle {
+		mid := midpoint(r)
+		return image.Rectangle{r.Min, mid}
+	}
+}
+
+// Quad3 resizes a layout to consume the bottom-left quadrant of its parent.
+func Quad3() ResizeFunc {
+	return func(r image.Rectangle) image.Rectangle {
+		mid := midpoint(r)
+		return image.Rect(r.Min.X, mid.Y, mid.X, r.Max.Y)
+	}
+}
+
+// Quad4 resizes a layout to consume the bottom-right quadrant of its parent.
+func Quad4() ResizeFunc {
+	return func(r image.Rectangle) image.Rectangle {
+		mid := midpoint(r)
+		return image.Rectangle{mid, r.Max}
+	}
+}
+
+// Inset resizes a layout to be inset some number of pixels from the edges of its parent.
+func Inset(top, right, bottom, left int) ResizeFunc {
+	if top < 0 {
+		panic(fmt.Sprintf("inset %d < 0", top))
+	} else if right < 0 {
+		panic(fmt.Sprintf("inset %d < 0", right))
+	} else if bottom < 0 {
+		panic(fmt.Sprintf("inset %d < 0", bottom))
+	} else if left < 0 {
+		panic(fmt.Sprintf("inset %d < 0", left))
+	}
+	return func(r image.Rectangle) image.Rectangle {
+		if r.Dx() < left+right {
+			r.Min.X = (r.Min.X + r.Max.X) / 2
+			r.Max.X = r.Min.X
+		} else {
+			r.Min.X += left
+			r.Max.X -= right
+		}
+		if r.Dy() < top+bottom {
+			r.Min.Y = (r.Min.Y + r.Max.Y) / 2
+			r.Max.Y = r.Min.Y
+		} else {
+			r.Min.Y += top
+			r.Max.Y -= bottom
+		}
+		return r
+	}
+}
+
+// InsetAll resizes as layout to be inset px pixels on all sides from the edges of its parent.
+func InsetAll(px int) ResizeFunc { return Inset(px, px, px, px) }
+
+// InsetTop resizes a layout to be inset px pixels from the top edge of its parent.
+func InsetTop(px int) ResizeFunc { return Inset(px, 0, 0, 0) }
+
+// InsetRight resizes a layout to be inset px pixels from the top edge of its parent.
+func InsetRight(px int) ResizeFunc { return Inset(0, px, 0, 0) }
+
+// InsetBottom resizes a layout to be inset px pixels from the top edge of its parent.
+func InsetBottom(px int) ResizeFunc { return Inset(0, 0, px, 0) }
+
+// InsetLeft resizes a layout to be inset px pixels from the top edge of its parent.
+func InsetLeft(px int) ResizeFunc { return Inset(0, 0, 0, px) }
+
+// midpoint returns the point in the middle of a rectangle.
+func midpoint(r image.Rectangle) image.Point {
+	return r.Min.Add(r.Max).Div(2)
+}