objects/layouts/grid.go

package layouts

import "math"
import "image"
import "git.tebibyte.media/tomo/tomo"

// Grid is a layout that arranges boxes in a grid formation with distinct rows
// and columns. It is great for creating forms.
type Grid struct {
	xExpand []bool
	yExpand []bool
}

// NewGrid creates a new grid layout. Rows and columns are specified as slices
// of booleans, where true means a row or column will expand and false means it
// will contract. Boxes are laid out left to right, then top to bottom. Boxes
// that go beyond the lengh of rows will be laid out according to columns, but
// they will not expand vertically.
func NewGrid (columns, rows []bool) *Grid {
	this := &Grid {
		xExpand: columns,
		yExpand: rows,
	}
	return this
}

func (this *Grid) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
	cols, rows := this.minimums(boxes)
	size := image.Pt (
		(len(cols) - 1) * hints.Gap.X,
		(len(rows) - 1) * hints.Gap.Y)
	for _, width  := range cols { size.X += width  }
	for _, height := range rows { size.Y += height }
	return size
}

func (this *Grid) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
	xExpand := func (index int) bool {
		return this.xExpand[index]
	}
	yExpand := func (index int) bool {
		if index < len(this.yExpand) { return this.yExpand[index] }
		return false
	}

	cols, rows := this.minimums(boxes)
	expand(hints, cols, hints.Bounds.Dx(), xExpand)
	expand(hints, rows, hints.Bounds.Dy(), yExpand)

	position := hints.Bounds.Min
	for index, box := range boxes {
		col, row := index % len(cols), index / len(cols)
		box.SetBounds(image.Rectangle {
			Min: position,
			Max: position.Add(image.Pt(cols[col], rows[row])),
		})
		if col == len(cols) - 1 {
			position.X = hints.Bounds.Min.X
			position.Y += rows[row] + hints.Gap.Y
		} else {
			position.X += cols[col] + hints.Gap.X
		}
	}
}

func (this *Grid) minimums (boxes []tomo.Box) ([]int, []int) {
	nCols, nRows := this.dimensions(boxes)
	cols,  rows  := make([]int, nCols), make([]int, nRows)

	for index, box := range boxes {
		col, row := index % len(cols), index / len(cols)
		minimum := box.MinimumSize()
		if cols[col] < minimum.X {
			cols[col] = minimum.X
		}
		if rows[row] < minimum.Y {
			rows[row] = minimum.Y
		}
	}
	
	return cols, rows
}

func (this *Grid) dimensions (boxes []tomo.Box) (int, int) {
	return len(this.xExpand), ceilDiv(len(boxes), len(this.xExpand)) 
}

func expand (hints tomo.LayoutHints, sizes []int, space int, expands func (int) bool) {
	gaps       := len(sizes) - 1
	freeSpace  := float64(space - hints.Gap.Y * gaps)
	nExpanding := 0; for index, minimum := range sizes {
		if expands(index) {
			nExpanding ++
		} else {
			freeSpace -= float64(minimum)
		}
	}
	expandingSize := freeSpace / float64(nExpanding)
	for index := range sizes {
		if expands(index) {
			sizes[index] = int(expandingSize)
		}
	}
}

func ceilDiv (x, y int) int {
	return int(math.Ceil(float64(x) / float64(y)))
}