space-ace-go/starfield.go

package main

import (
	"fmt"
	"math/rand"
	"red-green/door"
	"strings"
)

type StarPos struct {
	Y int
	X int
}

type StarInfo struct {
	Symbol int
	Color  bool
}

/*
StarField holds the information needed to render a starfield.
*/
type StarField struct {
	MX  int
	MY  int
	Sky map[StarPos]StarInfo
}

// Make a new StarPos in the StarField Sky.
func (s *StarField) make_pos(RNG *rand.Rand) StarPos {
	for {
		pos := StarPos{X: RNG.Intn(s.MX), Y: RNG.Intn(s.MY)}
		_, found := (*s).Sky[pos]
		if !found {
			return pos
		}
	}
}

// Regenerate a StarField structure.
// This uses make_pos to find a new unused position.
// This needs a seeded rand.Rand.
func (s *StarField) Regenerate(RNG *rand.Rand) {
	s.MX = door.Width
	s.MY = door.Height

	max_stars := ((s.MX * s.MY) / 40)
	s.Sky = make(map[StarPos]StarInfo, max_stars)

	for i := 0; i < max_stars; i++ {
		pos := s.make_pos(RNG)
		info := StarInfo{Symbol: i % 2, Color: i%5 < 2}
		s.Sky[pos] = info
	}
}

// Display StarField.
// This optimizes the output.  Uses CURSOR LEFT/RIGHT
// \x1b[C or \x1b[D to optimize output.
func (s *StarField) Display(d *door.Door) {
	white := door.ColorText("WHITE")
	dark := door.ColorText("BOLD BLACK")

	d.Write(door.Reset + door.Clrscr)
	var stars [2]string
	stars[0] = "."
	if door.Unicode {
		stars[1] = "\u2219"
	} else {
		stars[1] = "\xf9"
	}

	var i int = 0
	var last_pos StarPos

	// maps in go are not sorted
	for pos, info := range s.Sky {
		use_goto := true

		if i != 0 {
			if pos.Y == last_pos.Y {
				dx := pos.X - last_pos.X
				// Sometimes pos.X < last_pos.X
				if dx == 0 {
					use_goto = false
				} else {
					if dx < 0 {
						// handle negative
						// fmt.Printf("from %#v to %#v\n", last_pos, pos)
						dx = -dx
						if dx < 5 {
							d.Write(strings.Repeat("\x08", dx))
						} else {
							d.Write(fmt.Sprintf("\x1b[%dD", dx))
						}
						use_goto = false
					} else {
						if dx < 5 {
							d.Write(strings.Repeat(" ", dx))
						} else {
							d.Write(fmt.Sprintf("\x1b[%dC", dx))
						}
						use_goto = false
					}
				}
			}
		}

		if use_goto {
			d.Write(door.Goto(pos.X, pos.Y))
		}

		if info.Color {
			d.Write(dark)
		} else {
			d.Write(white)
		}
		d.Write(stars[info.Symbol])
		last_pos = pos
		last_pos.X++
		i++
	}
}