// vim: shiftwidth=4 tabstop=4 noexpandtab

package main

import (
	"github.com/go-gl/mathgl/mgl32"
)

// Point represents a three-dimensional point in space.
type Point struct {
	scalars [3]float32  // x = scalars[0], y = scalars[1], z = scalars[2]
}

// Triangle is a geometrical triangle defined by three points.
type Triangle struct {
	points [3]*Point
}

// Surface is a slice of triangles.
type Surface struct {
	triangles []*Triangle
}

// getHomeView returns a transformation which shows the given Surface in the
// center of the window.
func (s Surface) getHomeView() mgl32.Mat4 {

	// evaluating the smallest and biggest values for x,y,z of the surface
	var min,max [3]float32
	for _,triangle := range(s.triangles) {
		for _,point := range(triangle.points) {
			for index,_ := range(min) {
				if point.scalars[index] < min[index] {
					min[index] = point.scalars[index]
				}
				if point.scalars[index] > max[index] {
					max[index] = point.scalars[index]
				}
			}
		}
	}

	// calculate center point
	var center Point
	for index,_ := range(min) {
		center.scalars[index] = (min[index] + max[index]) / 2
	}

	// calculate zoom
	var zoom,zoomX,zoomY float32
	const fillFactor float32 = 0.8
	zoomX = (2 / (max[0] - min[0])) * fillFactor
	zoomY = (2 / (max[1] - min[1])) * fillFactor
	if zoomX > zoomY {
		zoom = zoomY
	} else {
		zoom = zoomX
	}

	// calculate and return transformation
	var trafo mgl32.Mat4 = mgl32.Ident4()
	trafo = mgl32.Translate3D(
		-center.scalars[0],
		-center.scalars[1],
		-center.scalars[2]).Mul4(trafo)
	trafo = mgl32.Scale3D(zoom, zoom, zoom).Mul4(trafo)

	return trafo
}