1 files changed, 191 insertions, 0 deletions
diff --git a/lib/ui/grid.go b/lib/ui/grid.go
new file mode 100644
index 0000000..ede7d0c
--- /dev/null
+++ b/lib/ui/grid.go
@@ -0,0 +1,191 @@
+package ui
+
+import (
+	"fmt"
+	"math"
+)
+
+type Grid struct {
+	rows         []GridSpec
+	rowLayout    []gridLayout
+	columns      []GridSpec
+	columnLayout []gridLayout
+	Cells        []*GridCell
+	onInvalidate func(d Drawable)
+	invalid      bool
+}
+
+const (
+	SIZE_EXACT  = iota
+	SIZE_WEIGHT = iota
+)
+
+// Specifies the layout of a single row or column
+type GridSpec struct {
+	// One of SIZE_EXACT or SIZE_WEIGHT
+	Strategy int
+	// If Strategy = SIZE_EXACT, this is the number of cells this row/col shall
+	// occupy. If SIZE_WEIGHT, the space left after all exact rows/cols are
+	// measured is distributed amonst the remainder weighted by this value.
+	Size int
+}
+
+// Used to cache layout of each row/column
+type gridLayout struct {
+	Offset int
+	Size   int
+}
+
+type GridCell struct {
+	Row     int
+	Column  int
+	RowSpan int
+	ColSpan int
+	Content Drawable
+	invalid bool
+}
+
+func NewGrid() *Grid {
+	return &Grid{invalid: true}
+}
+
+func (cell *GridCell) At(row, col int) *GridCell {
+	cell.Row = row
+	cell.Column = col
+	return cell
+}
+
+func (cell *GridCell) Span(rows, cols int) *GridCell {
+	cell.RowSpan = rows
+	cell.ColSpan = cols
+	return cell
+}
+
+func (grid *Grid) Rows(spec []GridSpec) *Grid {
+	grid.rows = spec
+	return grid
+}
+
+func (grid *Grid) Columns(spec []GridSpec) *Grid {
+	grid.columns = spec
+	return grid
+}
+
+func (grid *Grid) Draw(ctx *Context) {
+	invalid := grid.invalid
+	if invalid {
+		grid.reflow(ctx)
+	}
+	for _, cell := range grid.Cells {
+		if !cell.invalid && !invalid {
+			continue
+		}
+		rows := grid.rowLayout[cell.Row : cell.Row+cell.RowSpan]
+		cols := grid.columnLayout[cell.Column : cell.Column+cell.ColSpan]
+		x := cols[0].Offset
+		y := rows[0].Offset
+		width := 0
+		height := 0
+		for _, col := range cols {
+			width += col.Size
+		}
+		for _, row := range rows {
+			height += row.Size
+		}
+		subctx := ctx.Subcontext(x, y, width, height)
+		cell.Content.Draw(subctx)
+	}
+}
+
+func (grid *Grid) reflow(ctx *Context) {
+	grid.rowLayout = nil
+	grid.columnLayout = nil
+	flow := func(specs *[]GridSpec, layouts *[]gridLayout, extent int) {
+		exact := 0
+		weight := 0
+		nweights := 0
+		for _, spec := range *specs {
+			if spec.Strategy == SIZE_EXACT {
+				exact += spec.Size
+			} else if spec.Strategy == SIZE_WEIGHT {
+				nweights += 1
+				weight += spec.Size
+			}
+		}
+		offset := 0
+		for _, spec := range *specs {
+			layout := gridLayout{Offset: offset}
+			if spec.Strategy == SIZE_EXACT {
+				layout.Size = spec.Size
+			} else if spec.Strategy == SIZE_WEIGHT {
+				size := float64(spec.Size) / float64(weight)
+				size *= float64(extent - exact)
+				layout.Size = int(math.Floor(size))
+			}
+			offset += layout.Size
+			*layouts = append(*layouts, layout)
+		}
+	}
+	flow(&grid.rows, &grid.rowLayout, ctx.Height())
+	flow(&grid.columns, &grid.columnLayout, ctx.Width())
+	grid.invalid = false
+}
+
+func (grid *Grid) invalidateLayout() {
+	grid.invalid = true
+	if grid.onInvalidate != nil {
+		grid.onInvalidate(grid)
+	}
+}
+
+func (grid *Grid) Invalidate() {
+	grid.invalidateLayout()
+	for _, cell := range grid.Cells {
+		cell.Content.Invalidate()
+	}
+}
+
+func (grid *Grid) OnInvalidate(onInvalidate func(d Drawable)) {
+	grid.onInvalidate = onInvalidate
+}
+
+func (grid *Grid) AddChild(content Drawable) *GridCell {
+	cell := &GridCell{
+		RowSpan: 1,
+		ColSpan: 1,
+		Content: content,
+		invalid: true,
+	}
+	grid.Cells = append(grid.Cells, cell)
+	cell.Content.OnInvalidate(grid.cellInvalidated)
+	cell.invalid = true
+	grid.invalidateLayout()
+	return cell
+}
+
+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
+		}
+	}
+	grid.invalidateLayout()
+}
+
+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)
+	}
+}