3 files changed, 177 insertions, 0 deletions
diff --git a/ui/context.go b/ui/context.go
new file mode 100644
index 00000000..9f2e2fe5
--- /dev/null
+++ b/ui/context.go
@@ -0,0 +1,95 @@
+package ui
+
+import (
+	"fmt"
+
+	"github.com/nsf/termbox-go"
+)
+
+// A context allows you to draw in a sub-region of the terminal
+type Context struct {
+	x      int
+	y      int
+	width  int
+	height int
+}
+
+func (ctx *Context) Width() int {
+	return ctx.width
+}
+
+func (ctx *Context) Height() int {
+	return ctx.height
+}
+
+func NewContext() *Context {
+	width, height := termbox.Size()
+	return &Context{0, 0, width, height}
+}
+
+func (ctx *Context) Subcontext(x, y, width, height int) *Context {
+	if x+width > ctx.width || y+height > ctx.height {
+		panic(fmt.Errorf("Attempted to create context larger than parent"))
+	}
+	return &Context{
+		x:      ctx.x + x,
+		y:      ctx.y + y,
+		width:  width,
+		height: height,
+	}
+}
+
+func (ctx *Context) SetCell(x, y int, ch rune, fg, bg termbox.Attribute) {
+	if x >= ctx.width || y >= ctx.height {
+		panic(fmt.Errorf("Attempted to draw outside of context"))
+	}
+	termbox.SetCell(ctx.x+x, ctx.y+y, ch, fg, bg)
+}
+
+func (ctx *Context) Printf(x, y int, ref termbox.Cell,
+	format string, a ...interface{}) {
+
+	if x >= ctx.width || y >= ctx.height {
+		panic(fmt.Errorf("Attempted to draw outside of context"))
+	}
+
+	str := fmt.Sprintf(format, a...)
+
+	x += ctx.x
+	y += ctx.y
+	old_x := x
+
+	newline := func() bool {
+		x = old_x
+		y++
+		return y < ctx.height
+	}
+	for _, ch := range str {
+		switch ch {
+		case '\n':
+			if !newline() {
+				return
+			}
+		case '\r':
+			x = old_x
+		default:
+			termbox.SetCell(x, y, ch, ref.Fg, ref.Bg)
+			x++
+			if x == old_x+ctx.width {
+				if !newline() {
+					return
+				}
+			}
+		}
+	}
+}
+
+func (ctx *Context) Fill(x, y, width, height int, ref termbox.Cell) {
+	_x := x
+	for ; y < height && y < ctx.height; y++ {
+		for ; x < width && x < ctx.width; x++ {
+			ctx.SetCell(x, y, ref.Ch, ref.Fg, ref.Bg)
+		}
+		x = _x
+	}
+}
diff --git a/ui/drawable.go b/ui/drawable.go
new file mode 100644
index 00000000..eb60463b
--- /dev/null
+++ b/ui/drawable.go
@@ -0,0 +1,8 @@
+package ui
+
+type Drawable interface {
+	// Called when this renderable should draw itself
+	Draw(ctx Context)
+	// Specifies a function to call when this cell needs to be redrawn
+	OnInvalidate(callback func(d Drawable))
+}
diff --git a/ui/grid.go b/ui/grid.go
new file mode 100644
index 00000000..fd0cab7b
--- /dev/null
+++ b/ui/grid.go
@@ -0,0 +1,74 @@
+package ui
+
+import "fmt"
+
+type Grid struct {
+	Rows         []DimSpec
+	Columns      []DimSpec
+	Cells        []*GridCell
+	onInvalidate func(d Drawable)
+}
+
+const (
+	SIZE_EXACT  = iota
+	SIZE_WEIGHT = iota
+)
+
+// Specifies the layout of a single row or column
+type DimSpec struct {
+	// One of SIZE_EXACT or SIZE_WEIGHT
+	Strategy uint
+	// If Strategy = SIZE_EXACT, this is the number of cells this dim shall
+	// occupy. If SIZE_WEIGHT, the space left after all exact dims are measured
+	// is distributed amonst the remaining dims weighted by this value.
+	Size *uint
+}
+
+type GridCell struct {
+	Row     uint
+	Column  uint
+	RowSpan uint
+	ColSpan uint
+	Content Drawable
+	invalid bool
+}
+
+func (grid *Grid) Draw(ctx Context) {
+	// TODO
+}
+
+func (grid *Grid) OnInvalidate(onInvalidate func(d Drawable)) {
+	grid.onInvalidate = onInvalidate
+}
+
+func (grid *Grid) AddChild(cell *GridCell) {
+	grid.Cells = append(grid.Cells, cell)
+	cell.Content.OnInvalidate(grid.cellInvalidated)
+	cell.invalid = true
+}
+
+func (grid *Grid) RemoveChild(cell *GridCell) {
+	for i, _cell := range grid.Cells {
+		if _cell == cell {
+			grid.Cells = append(grid.Cells[:i], grid.Cells[i+1:]...)
+			break
+		}
+	}
+}
+
+func (grid *Grid) cellInvalidated(drawable Drawable) {
+	var cell *GridCell
+	for _, cell = range grid.Cells {
+		if cell.Content == drawable {
+			break
+		}
+		cell = nil
+	}
+	if cell == nil {
+		panic(fmt.Errorf("Attempted to invalidate unknown cell"))
+	}
+	cell.invalid = true
+	if grid.onInvalidate != nil {
+		grid.onInvalidate(grid)
+	}
+}