package upath

import "math"
import "image"

// P creates a path fom a list of integers that form X-Y pairs.
func P (data ...int) []image.Point {
	result := make([]image.Point, len(data) / 2)
	for index := range result {
		result[index].X = data[index * 2]
		result[index].Y = data[index * 2 + 1]
	}
	return result
}

// Lerp linearally interpolates between two paths. If the paths differ in
// length, the returned path will only be as long as the smaller one.
func Lerp (fac float64, start, end []image.Point) []image.Point {
	result := make([]image.Point, len(start))
	for index, startPt := range start {
		if index >= len(end) { return result[:index] }
		endPt := end[index]
		result[index] = image.Pt (
			lerp(fac, startPt.X, endPt.X),
			lerp(fac, startPt.Y, endPt.Y))
	}
	return result
}

// Distance returns the distance between two points.
func Distance (start, end image.Point) float64 {
	delta := start.Sub(end)
	return math.Sqrt(float64(delta.X * delta.X) + float64(delta.Y * delta.Y))
}

func lerp (fac float64, x, y int) int {
	return int(float64(x) * fac + float64(y) * (1.0 - fac))
}