// +build example
package main
import (
"fmt"
"image"
"image/color"
_ "image/jpeg"
"log"
"math"
"github.com/hajimehoshi/ebiten"
"github.com/hajimehoshi/ebiten/ebitenutil"
)
const (
screenWidth = 320
screenHeight = 240
maxAngle = 256
maxLean = 16
)
var (
skyColor = color.RGBA{0x66, 0xcc, 0xff, 0xff}
thePlayer = &player{
x16: 16 * 100,
y16: 16 * 200,
angle: maxAngle * 3 / 4,
}
gophersImage *ebiten.Image
repeatedGophersImage *ebiten.Image
groundImage *ebiten.Image
perspectiveGroundImage *ebiten.Image
fogImage *ebiten.Image
)
func init() {
var err error
gophersImage, _, err = ebitenutil.NewImageFromFile("_resources/images/gophers.jpg", ebiten.FilterDefault)
if err != nil {
panic(err)
}
groundImage, _ = ebiten.NewImage(screenWidth*2, screenHeight*2/3+50, ebiten.FilterDefault)
perspectiveGroundImage, _ = ebiten.NewImage(screenWidth*2, screenHeight, ebiten.FilterDefault)
const repeat = 5
w, h := gophersImage.Size()
repeatedGophersImage, _ = ebiten.NewImage(w*repeat, h*repeat, ebiten.FilterDefault)
for j := 0; j < repeat; j++ {
for i := 0; i < repeat; i++ {
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(float64(w*i), float64(h*j))
repeatedGophersImage.DrawImage(gophersImage, op)
}
}
const fogHeight = 8
w, _ = perspectiveGroundImage.Size()
fogRGBA := image.NewRGBA(image.Rect(0, 0, w, fogHeight))
for j := 0; j < fogHeight; j++ {
a := uint32(float64(fogHeight-1-j) * 0xff / (fogHeight - 1))
clr := skyColor
r, g, b, oa := uint32(clr.R), uint32(clr.G), uint32(clr.B), uint32(clr.A)
clr.R = uint8(r * a / oa)
clr.G = uint8(g * a / oa)
clr.B = uint8(b * a / oa)
clr.A = uint8(a)
for i := 0; i < w; i++ {
fogRGBA.SetRGBA(i, j, clr)
}
}
fogImage, _ = ebiten.NewImageFromImage(fogRGBA, ebiten.FilterDefault)
}
// player represents the current airship's position.
type player struct {
// x16, y16 represents the position in XY plane in fixed float format.
// The fractional part has 16 bits of precision.
x16 int
y16 int
// angle represents the player's angle in XY plane.
// angle takes an integer value in [0, maxAngle).
angle int
// lean represents the player's leaning.
// lean takes an integer value in [-maxLean, maxLean].
lean int
}
func round(x float64) float64 {
return math.Floor(x + 0.5)
}
// MoveForward moves the player p forward.
func (p *player) MoveForward() {
w, h := gophersImage.Size()
mx := w * 16
my := h * 16
s, c := math.Sincos(float64(p.angle) * 2 * math.Pi / maxAngle)
p.x16 += int(round(16*c) * 2)
p.y16 += int(round(16*s) * 2)
for mx <= p.x16 {
p.x16 -= mx
}
for my <= p.y16 {
p.y16 -= my
}
for p.x16 < 0 {
p.x16 += mx
}
for p.y16 < 0 {
p.y16 += my
}
}
// RotateRight rotates the player p in the right direction.
func (p *player) RotateRight() {
p.angle++
if maxAngle <= p.angle {
p.angle -= maxAngle
}
p.lean++
if maxLean < p.lean {
p.lean = maxLean
}
}
// RotateLeft rotates the player p in the left direction.
func (p *player) RotateLeft() {
p.angle--
if p.angle < 0 {
p.angle += maxAngle
}
p.lean--
if p.lean < -maxLean {
p.lean = -maxLean
}
}
// Stabilize tries to move the player in the stable position (lean).
func (p *player) Stabilize() {
if 0 < p.lean {
p.lean--
}
if p.lean < 0 {
p.lean++
}
}
// Position returns the player p's position.
func (p *player) Position() (int, int) {
return p.x16, p.y16
}
// Angle returns the player p's angle.
func (p *player) Angle() int {
return p.angle
}
// updateGroundImage updates the ground image according to the current player's position.
func updateGroundImage(ground *ebiten.Image) {
ground.Clear()
x16, y16 := thePlayer.Position()
a := thePlayer.Angle()
gw, gh := ground.Size()
w, h := gophersImage.Size()
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(float64(-x16)/16, float64(-y16)/16)
op.GeoM.Translate(float64(-w*2), float64(-h*2))
op.GeoM.Rotate(float64(-a)*2*math.Pi/maxAngle + math.Pi*3.0/2.0)
op.GeoM.Translate(float64(gw)/2, float64(gh)-32)
ground.DrawImage(repeatedGophersImage, op)
}
// drawGroundImage draws the ground image to the given screen image.
func drawGroundImage(screen *ebiten.Image, ground *ebiten.Image) {
perspectiveGroundImage.Clear()
gw, _ := ground.Size()
pw, ph := perspectiveGroundImage.Size()
for j := 0; j < ph; j++ {
// z is in [1.5, 0.01]
rate := float64(j) / float64(ph)
z := (1-rate)*1.5 + rate*0.01
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(-float64(pw)/2, 0)
op.GeoM.Scale(1/z, 4) // 4 is an arbitrary number not to make empty lines.
op.GeoM.Translate(float64(pw)/2, float64(j)/z)
src := image.Rect(0, j, gw, j+1)
op.SourceRect = &src
perspectiveGroundImage.DrawImage(ground, op)
}
perspectiveGroundImage.DrawImage(fogImage, nil)
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(-float64(pw)/2, 0)
op.GeoM.Rotate(-1 * float64(thePlayer.lean) / maxLean * math.Pi / 8)
op.GeoM.Translate(float64(screenWidth)/2, screenHeight/3)
screen.DrawImage(perspectiveGroundImage, op)
}
func update(screen *ebiten.Image) error {
// Manipulate the player by the input.
if ebiten.IsKeyPressed(ebiten.KeySpace) {
thePlayer.MoveForward()
}
rotated := false
if ebiten.IsKeyPressed(ebiten.KeyRight) {
thePlayer.RotateRight()
rotated = true
}
if ebiten.IsKeyPressed(ebiten.KeyLeft) {
thePlayer.RotateLeft()
rotated = true
}
if !rotated {
thePlayer.Stabilize()
}
if ebiten.IsRunningSlowly() {
return nil
}
// Draw the ground image.
screen.Fill(skyColor)
updateGroundImage(groundImage)
drawGroundImage(screen, groundImage)
// Draw the message.
tutrial := "Space: Move forward\nLeft/Right: Rotate"
msg := fmt.Sprintf("FPS: %0.2f\n%s", ebiten.CurrentFPS(), tutrial)
ebitenutil.DebugPrint(screen, msg)
return nil
}
func main() {
if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Air Ship (Ebiten Demo)"); err != nil {
log.Fatal(err)
}
}