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main.go
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main.go
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// Copyright 2019 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.
package main
import (
"bytes"
"errors"
"fmt"
"image"
"image/color"
_ "image/png"
"log"
"math"
"sort"
"github.com/hajimehoshi/ebiten/v2"
"github.com/hajimehoshi/ebiten/v2/ebitenutil"
"github.com/hajimehoshi/ebiten/v2/examples/resources/images"
"github.com/hajimehoshi/ebiten/v2/inpututil"
"github.com/hajimehoshi/ebiten/v2/vector"
)
const (
screenWidth = 240
screenHeight = 240
padding = 20
)
var (
bgImage *ebiten.Image
shadowImage = ebiten.NewImage(screenWidth, screenHeight)
triangleImage = ebiten.NewImage(screenWidth, screenHeight)
)
func init() {
// Decode an image from the image file's byte slice.
img, _, err := image.Decode(bytes.NewReader(images.Tile_png))
if err != nil {
log.Fatal(err)
}
bgImage = ebiten.NewImageFromImage(img)
triangleImage.Fill(color.White)
}
type line struct {
X1, Y1, X2, Y2 float64
}
func (l *line) angle() float64 {
return math.Atan2(l.Y2-l.Y1, l.X2-l.X1)
}
type object struct {
walls []line
}
func (o object) points() [][2]float64 {
// Get one of the endpoints for all segments,
// + the startpoint of the first one, for non-closed paths
var points [][2]float64
for _, wall := range o.walls {
points = append(points, [2]float64{wall.X2, wall.Y2})
}
p := [2]float64{o.walls[0].X1, o.walls[0].Y1}
if p[0] != points[len(points)-1][0] && p[1] != points[len(points)-1][1] {
points = append(points, [2]float64{o.walls[0].X1, o.walls[0].Y1})
}
return points
}
func newRay(x, y, length, angle float64) line {
return line{
X1: x,
Y1: y,
X2: x + length*math.Cos(angle),
Y2: y + length*math.Sin(angle),
}
}
// intersection calculates the intersection of given two lines.
func intersection(l1, l2 line) (float64, float64, bool) {
// https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line
denom := (l1.X1-l1.X2)*(l2.Y1-l2.Y2) - (l1.Y1-l1.Y2)*(l2.X1-l2.X2)
tNum := (l1.X1-l2.X1)*(l2.Y1-l2.Y2) - (l1.Y1-l2.Y1)*(l2.X1-l2.X2)
uNum := -((l1.X1-l1.X2)*(l1.Y1-l2.Y1) - (l1.Y1-l1.Y2)*(l1.X1-l2.X1))
if denom == 0 {
return 0, 0, false
}
t := tNum / denom
if t > 1 || t < 0 {
return 0, 0, false
}
u := uNum / denom
if u > 1 || u < 0 {
return 0, 0, false
}
x := l1.X1 + t*(l1.X2-l1.X1)
y := l1.Y1 + t*(l1.Y2-l1.Y1)
return x, y, true
}
// rayCasting returns a slice of line originating from point cx, cy and intersecting with objects
func rayCasting(cx, cy float64, objects []object) []line {
const rayLength = 1000 // something large enough to reach all objects
var rays []line
for _, obj := range objects {
// Cast two rays per point
for _, p := range obj.points() {
l := line{cx, cy, p[0], p[1]}
angle := l.angle()
for _, offset := range []float64{-0.005, 0.005} {
points := [][2]float64{}
ray := newRay(cx, cy, rayLength, angle+offset)
// Unpack all objects
for _, o := range objects {
for _, wall := range o.walls {
if px, py, ok := intersection(ray, wall); ok {
points = append(points, [2]float64{px, py})
}
}
}
// Find the point closest to start of ray
min := math.Inf(1)
minI := -1
for i, p := range points {
d2 := (cx-p[0])*(cx-p[0]) + (cy-p[1])*(cy-p[1])
if d2 < min {
min = d2
minI = i
}
}
rays = append(rays, line{cx, cy, points[minI][0], points[minI][1]})
}
}
}
// Sort rays based on angle, otherwise light triangles will not come out right
sort.Slice(rays, func(i int, j int) bool {
return rays[i].angle() < rays[j].angle()
})
return rays
}
func (g *Game) handleMovement() {
if ebiten.IsKeyPressed(ebiten.KeyD) || ebiten.IsKeyPressed(ebiten.KeyArrowRight) {
g.px += 4
}
if ebiten.IsKeyPressed(ebiten.KeyS) || ebiten.IsKeyPressed(ebiten.KeyArrowDown) {
g.py += 4
}
if ebiten.IsKeyPressed(ebiten.KeyA) || ebiten.IsKeyPressed(ebiten.KeyArrowLeft) {
g.px -= 4
}
if ebiten.IsKeyPressed(ebiten.KeyW) || ebiten.IsKeyPressed(ebiten.KeyArrowUp) {
g.py -= 4
}
// +1/-1 is to stop player before it reaches the border
if g.px >= screenWidth-padding {
g.px = screenWidth - padding - 1
}
if g.px <= padding {
g.px = padding + 1
}
if g.py >= screenHeight-padding {
g.py = screenHeight - padding - 1
}
if g.py <= padding {
g.py = padding + 1
}
}
func rayVertices(x1, y1, x2, y2, x3, y3 float64) []ebiten.Vertex {
return []ebiten.Vertex{
{DstX: float32(x1), DstY: float32(y1), SrcX: 0, SrcY: 0, ColorR: 1, ColorG: 1, ColorB: 1, ColorA: 1},
{DstX: float32(x2), DstY: float32(y2), SrcX: 0, SrcY: 0, ColorR: 1, ColorG: 1, ColorB: 1, ColorA: 1},
{DstX: float32(x3), DstY: float32(y3), SrcX: 0, SrcY: 0, ColorR: 1, ColorG: 1, ColorB: 1, ColorA: 1},
}
}
type Game struct {
showRays bool
px, py int
objects []object
}
func (g *Game) Update() error {
if inpututil.IsKeyJustPressed(ebiten.KeyEscape) {
return errors.New("game ended by player")
}
if inpututil.IsKeyJustPressed(ebiten.KeyR) {
g.showRays = !g.showRays
}
g.handleMovement()
return nil
}
func (g *Game) Draw(screen *ebiten.Image) {
// Reset the shadowImage
shadowImage.Fill(color.Black)
rays := rayCasting(float64(g.px), float64(g.py), g.objects)
// Subtract ray triangles from shadow
opt := &ebiten.DrawTrianglesOptions{}
opt.Address = ebiten.AddressRepeat
opt.Blend = ebiten.BlendSourceOut
for i, line := range rays {
nextLine := rays[(i+1)%len(rays)]
// Draw triangle of area between rays
v := rayVertices(float64(g.px), float64(g.py), nextLine.X2, nextLine.Y2, line.X2, line.Y2)
shadowImage.DrawTriangles(v, []uint16{0, 1, 2}, triangleImage, opt)
}
// Draw background
screen.DrawImage(bgImage, nil)
if g.showRays {
// Draw rays
for _, r := range rays {
vector.StrokeLine(screen, float32(r.X1), float32(r.Y1), float32(r.X2), float32(r.Y2), 1, color.RGBA{255, 255, 0, 150}, true)
}
}
// Draw shadow
op := &ebiten.DrawImageOptions{}
op.ColorScale.ScaleAlpha(0.7)
screen.DrawImage(shadowImage, op)
// Draw walls
for _, obj := range g.objects {
for _, w := range obj.walls {
vector.StrokeLine(screen, float32(w.X1), float32(w.Y1), float32(w.X2), float32(w.Y2), 1, color.RGBA{255, 0, 0, 255}, true)
}
}
// Draw player as a rect
vector.DrawFilledRect(screen, float32(g.px)-2, float32(g.py)-2, 4, 4, color.Black, true)
vector.DrawFilledRect(screen, float32(g.px)-1, float32(g.py)-1, 2, 2, color.RGBA{255, 100, 100, 255}, true)
if g.showRays {
ebitenutil.DebugPrintAt(screen, "R: hide rays", padding, 0)
} else {
ebitenutil.DebugPrintAt(screen, "R: show rays", padding, 0)
}
ebitenutil.DebugPrintAt(screen, "WASD: move", 160, 0)
ebitenutil.DebugPrintAt(screen, fmt.Sprintf("TPS: %0.2f", ebiten.ActualTPS()), 51, 51)
ebitenutil.DebugPrintAt(screen, fmt.Sprintf("Rays: 2*%d", len(rays)/2), padding, 222)
}
func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
return screenWidth, screenHeight
}
func rect(x, y, w, h float64) []line {
return []line{
{x, y, x, y + h},
{x, y + h, x + w, y + h},
{x + w, y + h, x + w, y},
{x + w, y, x, y},
}
}
func main() {
g := &Game{
px: screenWidth / 2,
py: screenHeight / 2,
}
// Add outer walls
g.objects = append(g.objects, object{rect(padding, padding, screenWidth-2*padding, screenHeight-2*padding)})
// Angled wall
g.objects = append(g.objects, object{[]line{{50, 110, 100, 150}}})
// Rectangles
g.objects = append(g.objects, object{rect(45, 50, 70, 20)})
g.objects = append(g.objects, object{rect(150, 50, 30, 60)})
ebiten.SetWindowSize(screenWidth*2, screenHeight*2)
ebiten.SetWindowTitle("Ray casting and shadows (Ebitengine Demo)")
if err := ebiten.RunGame(g); err != nil {
log.Fatal(err)
}
}