88 lines
1.9 KiB
Go
88 lines
1.9 KiB
Go
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// Package geo implements basic geometric concepts used by gim
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package geo
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import "math"
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// XY describes a 2-dimensional position or vector. The origin of the
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// 2-dimensional space is a 0,0, with the x-axis going to the left and the
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// y-axis going down.
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type XY [2]int
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// Zero is the zero point, or a zero vector, depending on what you're doing
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var Zero = XY{0, 0}
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// Unit vectors
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var (
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Up = XY{0, -1}
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Down = XY{0, 1}
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Left = XY{-1, 0}
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Right = XY{1, 0}
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)
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// Add returns the result of adding the two XYs' fields individually
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func (xy XY) Add(xy2 XY) XY {
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xy[0] += xy2[0]
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xy[1] += xy2[1]
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return xy
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}
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// Mul returns the result of multiplying the two XYs' fields individually
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func (xy XY) Mul(xy2 XY) XY {
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xy[0] *= xy2[0]
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xy[1] *= xy2[1]
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return xy
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}
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// Scale returns the result of multiplying both of the XY's fields by the scalar
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func (xy XY) Scale(scalar int) XY {
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return xy.Mul(XY{scalar, scalar})
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}
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// Inv inverses the XY, a shortcut for xy.Scale(-1)
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func (xy XY) Inv() XY {
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return xy.Scale(-1)
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}
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// Sub subtracts xy2 from xy and returns the result. A shortcut for
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// xy.Add(xy2.Inv())
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func (xy XY) Sub(xy2 XY) XY {
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return xy.Add(xy2.Inv())
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}
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func round(f float64, r int) int {
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switch {
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case r < 0:
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f = math.Floor(f)
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case r == 0:
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if f < 0 {
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f = math.Ceil(f - 0.5)
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}
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f = math.Floor(f + 0.5)
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case r > 0:
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f = math.Ceil(f)
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}
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return int(f)
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}
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func (xy XY) toF64() [2]float64 {
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return [2]float64{
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float64(xy[0]),
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float64(xy[1]),
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}
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}
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// Midpoint returns the midpoint between the two XYs. The rounder indicates what
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// to do about non-whole values when they're come across:
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// - rounder < 0 : floor
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// - rounder = 0 : round
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// - rounder > 0 : ceil
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func (xy XY) Midpoint(xy2 XY, rounder int) XY {
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xyf, xy2f := xy.toF64(), xy2.toF64()
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xf := xyf[0] + ((xy2f[0] - xyf[0]) / 2)
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yf := xyf[1] + ((xy2f[1] - xyf[1]) / 2)
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return XY{
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round(xf, rounder),
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round(yf, rounder),
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}
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}
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