ichigo/engine/box.go

package engine

import "image"

// Box describes an axis-aligned rectangular prism.
type Box struct {
	Min, Max Point3
}

// String returns a string representation of b like "(3,4,5)-(6,5,8)".
func (b Box) String() string {
	return b.Min.String() + "-" + b.Max.String()
}

// Empty reports whether the box contains no points.
func (b Box) Empty() bool {
	return b.Min.X >= b.Max.X || b.Min.Y >= b.Max.Y || b.Min.Z >= b.Max.Z
}

// Eq reports whether b and c contain the same set of points. All empty boxes
// are considered equal.
func (b Box) Eq(c Box) bool {
	return b == c || b.Empty() && c.Empty()
}

// Overlaps reports whether b and c have non-empty intersection.
func (b Box) Overlaps(c Box) bool {
	return !b.Empty() && !c.Empty() &&
		b.Min.X < c.Max.X && c.Min.X < b.Max.X &&
		b.Min.Y < c.Max.Y && c.Min.Y < b.Max.Y &&
		b.Min.Z < c.Max.Z && c.Min.Z < b.Max.Z
}

// Size returns b's width, height, and depth.
func (b Box) Size() Point3 {
	return b.Max.Sub(b.Min)
}

// Back returns an image.Rectangle representing the back of the box, using
// the given projection π.
func (b Box) Back(π image.Point) image.Rectangle {
	b.Max.Z = b.Min.Z
	return image.Rectangle{
		Min: b.Min.IsoProject(π),
		Max: b.Max.IsoProject(π),
	}
}

// Front returns an image.Rectangle representing the front of the box, using
// the given projection π.
func (b Box) Front(π image.Point) image.Rectangle {
	b.Min.Z = b.Max.Z
	return image.Rectangle{
		Min: b.Min.IsoProject(π),
		Max: b.Max.IsoProject(π),
	}
}

// XY returns the image.Rectangle representing the box if we forgot about Z.
func (b Box) XY() image.Rectangle {
	return image.Rectangle{
		Min: b.Min.XY(),
		Max: b.Max.XY(),
	}
}