ginger/gim/geo/rect.go

package geo

import (
	"fmt"
)

// Rect describes a rectangle based on the position of its top-left corner and
// size
type Rect struct {
	TopLeft XY
	Size    XY
}

// Edge describes a straight edge starting at its first XY and ending at its
// second
type Edge [2]XY

// EdgeCoord returns the coordinate of the edge indicated by the given direction
// (Up, Down, Left, or Right). The coordinate will be for the axis applicable to
// the direction, so for Left/Right it will be the x coordinate and for Up/Down
// the y.
func (r Rect) EdgeCoord(dir XY) int {
	switch dir {
	case Up:
		return r.TopLeft[1]
	case Down:
		return r.TopLeft[1] + r.Size[1] - 1
	case Left:
		return r.TopLeft[0]
	case Right:
		return r.TopLeft[0] + r.Size[0] - 1
	default:
		panic(fmt.Sprintf("unsupported direction: %#v", dir))
	}
}

// Corner returns the position of the corner identified by the given directions
// (Left/Right, Up/Down)
func (r Rect) Corner(xDir, yDir XY) XY {
	switch {
	case r.Size[0] == 0 || r.Size[1] == 0:
		panic(fmt.Sprintf("rectangle with non-multidimensional size has no corners: %v", r.Size))
	case xDir == Left && yDir == Up:
		return r.TopLeft
	case xDir == Right && yDir == Up:
		return r.TopLeft.Add(r.Size.Mul(Right)).Add(XY{-1, 0})
	case xDir == Left && yDir == Down:
		return r.TopLeft.Add(r.Size.Mul(Down)).Add(XY{0, -1})
	case xDir == Right && yDir == Down:
		return r.TopLeft.Add(r.Size).Add(XY{-1, -1})
	default:
		panic(fmt.Sprintf("unsupported Corner args: %v, %v", xDir, yDir))
	}
}

// Edge returns an Edge instance for the edge of the Rect indicated by the given
// direction (Up, Down, Left, or Right). secDir indicates the direction the
// returned Edge should be pointing (i.e. the order of its XY's) and must be
// perpendicular to dir
func (r Rect) Edge(dir, secDir XY) Edge {
	var e Edge
	switch dir {
	case Up:
		e[0], e[1] = r.Corner(Left, Up), r.Corner(Right, Up)
	case Down:
		e[0], e[1] = r.Corner(Left, Down), r.Corner(Right, Down)
	case Left:
		e[0], e[1] = r.Corner(Left, Up), r.Corner(Left, Down)
	case Right:
		e[0], e[1] = r.Corner(Right, Up), r.Corner(Right, Down)
	default:
		panic(fmt.Sprintf("unsupported direction: %#v", dir))
	}

	switch secDir {
	case Left, Up:
		e[0], e[1] = e[1], e[0]
	default:
		// do nothing
	}
	return e
}

// Midpoint returns the point which is the midpoint of the Edge
func (e Edge) Midpoint() XY {
	return e[0].Midpoint(e[1])
}

func (r Rect) halfSize() XY {
	return r.Size.Div(XY{2, 2})
}

// Center returns the centerpoint of the rectangle.
func (r Rect) Center() XY {
	return r.TopLeft.Add(r.halfSize())
}

// Translate returns an instance of Rect which is the same as this one but
// translated by the given amount.
func (r Rect) Translate(by XY) Rect {
	r.TopLeft = r.TopLeft.Add(by)
	return r
}

// Centered returns an instance of Rect which is this one but translated to be
// centered on the given point.
func (r Rect) Centered(on XY) Rect {
	r.TopLeft = on.Sub(r.halfSize())
	return r
}

// Union returns the smallest Rect which encompasses the given Rect and the one
// being called upon.
func (r Rect) Union(r2 Rect) Rect {
	if r.Size == Zero {
		return r2
	} else if r2.Size == Zero {
		return r
	}

	tl := r.TopLeft.Min(r2.TopLeft)
	br := r.Corner(Right, Down).Max(r2.Corner(Right, Down))
	return Rect{
		TopLeft: tl,
		Size:    br.Sub(tl).Add(XY{1, 1}),
	}
}