ebiten/examples/airship/main.go

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// Copyright 2016 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
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//go:build example
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// +build example
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package main
import (
"bytes"
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"fmt"
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"image"
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"image/color"
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_ "image/jpeg"
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"log"
"math"
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"github.com/hajimehoshi/ebiten/v2"
"github.com/hajimehoshi/ebiten/v2/ebitenutil"
"github.com/hajimehoshi/ebiten/v2/examples/resources/images"
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)
const (
screenWidth = 640
screenHeight = 480
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maxAngle = 256
maxLean = 16
)
var (
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skyColor = color.RGBA{0x66, 0xcc, 0xff, 0xff}
gophersImage *ebiten.Image
repeatedGophersImage *ebiten.Image
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)
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func init() {
// Decode an image from the image file's byte slice.
// Now the byte slice is generated with //go:generate for Go 1.15 or older.
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// If you use Go 1.16 or newer, it is strongly recommended to use //go:embed to embed the image file.
// See https://pkg.go.dev/embed for more details.
img, _, err := image.Decode(bytes.NewReader(images.Gophers_jpg))
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if err != nil {
log.Fatal(err)
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}
gophersImage = ebiten.NewImageFromImage(img)
const (
xrepeat = 7
yrepeat = 8
)
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w, h := gophersImage.Size()
repeatedGophersImage = ebiten.NewImage(w*xrepeat, h*yrepeat)
for j := 0; j < yrepeat; j++ {
for i := 0; i < xrepeat; i++ {
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op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(float64(w*i), float64(h*j))
repeatedGophersImage.DrawImage(gophersImage, op)
}
}
}
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// player represents the current airship's position.
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type player struct {
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// 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).
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angle int
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// lean represents the player's leaning.
// lean takes an integer value in [-maxLean, maxLean].
lean int
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}
func round(x float64) float64 {
return math.Floor(x + 0.5)
}
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// MoveForward moves the player p forward.
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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)
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p.x16 += int(round(16*c) * 2)
p.y16 += int(round(16*s) * 2)
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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
}
}
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// RotateRight rotates the player p in the right direction.
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func (p *player) RotateRight() {
p.angle++
if maxAngle <= p.angle {
p.angle -= maxAngle
}
p.lean++
if maxLean < p.lean {
p.lean = maxLean
}
}
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// RotateLeft rotates the player p in the left direction.
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func (p *player) RotateLeft() {
p.angle--
if p.angle < 0 {
p.angle += maxAngle
}
p.lean--
if p.lean < -maxLean {
p.lean = -maxLean
}
}
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// Stabilize tries to move the player in the stable position (lean).
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func (p *player) Stabilize() {
if 0 < p.lean {
p.lean--
}
if p.lean < 0 {
p.lean++
}
}
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// Position returns the player p's position.
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func (p *player) Position() (int, int) {
return p.x16, p.y16
}
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// Angle returns the player p's angle.
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func (p *player) Angle() int {
return p.angle
}
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// updateGroundImage updates the ground image according to the current player's position.
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func (g *Game) updateGroundImage(ground *ebiten.Image) {
ground.Clear()
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x16, y16 := g.player.Position()
a := g.player.Angle()
rw, rh := repeatedGophersImage.Size()
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gw, gh := ground.Size()
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(float64(-x16)/16, float64(-y16)/16)
op.GeoM.Translate(float64(-rw)/2, float64(-rh)/2)
op.GeoM.Rotate(float64(-a)*2*math.Pi/maxAngle + math.Pi*3.0/2.0)
op.GeoM.Translate(float64(gw)/2, float64(gh)/2)
ground.DrawImage(repeatedGophersImage, op)
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}
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// drawGroundImage draws the ground image to the given screen image.
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func (g *Game) drawGroundImage(screen *ebiten.Image, ground *ebiten.Image) {
g.perspectiveGroundImage.Clear()
gw, _ := ground.Size()
pw, ph := g.perspectiveGroundImage.Size()
for j := 0; j < ph; j++ {
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// z is in [2, -1]
rate := float64(j) / float64(ph)
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z := (1-rate)*2 + rate*-1
// Avoid too small z, or the scale (1/z) can be too big.
if z <= 0.1 {
break
}
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op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(-float64(pw)/2, 0)
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op.GeoM.Scale(1/z, 8) // 8 is an arbitrary number not to make empty lines.
op.GeoM.Translate(float64(pw)/2, float64(j)/z)
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g.perspectiveGroundImage.DrawImage(ground.SubImage(image.Rect(0, j, gw, j+1)).(*ebiten.Image), op)
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}
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g.perspectiveGroundImage.DrawImage(g.fogImage, nil)
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op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(-float64(pw)/2, 0)
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op.GeoM.Rotate(-1 * float64(g.player.lean) / maxLean * math.Pi / 8)
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op.GeoM.Translate(float64(screenWidth)/2, screenHeight/3)
screen.DrawImage(g.perspectiveGroundImage, op)
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}
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type Game struct {
player *player
groundImage *ebiten.Image
perspectiveGroundImage *ebiten.Image
fogImage *ebiten.Image
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}
func NewGame() *Game {
g := &Game{
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player: &player{
x16: 16 * 100,
y16: 16 * 200,
angle: maxAngle * 3 / 4,
},
groundImage: ebiten.NewImage(screenWidth*3, screenHeight*2/3+200),
perspectiveGroundImage: ebiten.NewImage(screenWidth*3, screenHeight),
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}
const fogHeight = 16
w, _ := g.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)
}
}
g.fogImage = ebiten.NewImageFromImage(fogRGBA)
return g
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}
func (g *Game) Update() error {
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// Manipulate the player by the input.
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if ebiten.IsKeyPressed(ebiten.KeySpace) {
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g.player.MoveForward()
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}
rotated := false
if ebiten.IsKeyPressed(ebiten.KeyArrowRight) {
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g.player.RotateRight()
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rotated = true
}
if ebiten.IsKeyPressed(ebiten.KeyArrowLeft) {
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g.player.RotateLeft()
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rotated = true
}
if !rotated {
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g.player.Stabilize()
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}
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return nil
}
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func (g *Game) Draw(screen *ebiten.Image) {
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// Draw the ground image.
screen.Fill(skyColor)
g.updateGroundImage(g.groundImage)
g.drawGroundImage(screen, g.groundImage)
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// Draw the message.
tutorial := "Space: Move forward\nLeft/Right: Rotate"
msg := fmt.Sprintf("TPS: %0.2f\nFPS: %0.2f\n%s", ebiten.ActualTPS(), ebiten.ActualFPS(), tutorial)
ebitenutil.DebugPrint(screen, msg)
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}
func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
return screenWidth, screenHeight
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}
func main() {
ebiten.SetWindowSize(screenWidth, screenHeight)
ebiten.SetWindowTitle("Air Ship (Ebitengine Demo)")
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if err := ebiten.RunGame(NewGame()); err != nil {
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log.Fatal(err)
}
}