ebiten/examples/masking/main.go

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// Copyright 2016 Hajime Hoshi
//
// 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.
// +build example
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package main
import (
"image"
"image/color"
_ "image/jpeg"
"log"
"math"
"github.com/hajimehoshi/ebiten"
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"github.com/hajimehoshi/ebiten/ebitenutil"
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)
const (
screenWidth = 320
screenHeight = 240
)
var (
gophersImage *ebiten.Image
fiveyearsImage *ebiten.Image
maskImage *ebiten.Image
spotLightImage *ebiten.Image
spotLightX = 0
spotLightY = 0
spotLightVX = 1
spotLightVY = 1
)
func update(screen *ebiten.Image) error {
spotLightX += spotLightVX
spotLightY += spotLightVY
if spotLightX < 0 {
spotLightX = -spotLightX
spotLightVX = -spotLightVX
}
if spotLightY < 0 {
spotLightY = -spotLightY
spotLightVY = -spotLightVY
}
w, h := spotLightImage.Size()
maxX, maxY := screenWidth-w, screenHeight-h
if maxX < spotLightX {
spotLightX = -spotLightX + 2*maxX
spotLightVX = -spotLightVX
}
if maxY < spotLightY {
spotLightY = -spotLightY + 2*maxY
spotLightVY = -spotLightVY
}
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if ebiten.IsRunningSlowly() {
return nil
}
maskImage.Clear()
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op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(float64(spotLightX), float64(spotLightY))
maskImage.DrawImage(spotLightImage, op)
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op = &ebiten.DrawImageOptions{}
op.CompositeMode = ebiten.CompositeModeSourceOut
maskImage.DrawImage(fiveyearsImage, op)
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screen.Fill(color.RGBA{0x00, 0x00, 0x80, 0xff})
screen.DrawImage(gophersImage, &ebiten.DrawImageOptions{})
screen.DrawImage(maskImage, &ebiten.DrawImageOptions{})
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return nil
}
func max(a, b int) int {
if a < b {
return b
}
return a
}
func min(a, b int) int {
if a < b {
return a
}
return b
}
func main() {
var err error
gophersImage, _, err = ebitenutil.NewImageFromFile(ebitenutil.JoinStringsIntoFilePath("_resources", "images", "gophers.jpg"), ebiten.FilterNearest)
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if err != nil {
log.Fatal(err)
}
fiveyearsImage, _, err = ebitenutil.NewImageFromFile(ebitenutil.JoinStringsIntoFilePath("_resources", "images", "fiveyears.jpg"), ebiten.FilterNearest)
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if err != nil {
log.Fatal(err)
}
maskImage, _ = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
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as := image.Point{128, 128}
a := image.NewAlpha(image.Rectangle{image.ZP, as})
for j := 0; j < as.Y; j++ {
for i := 0; i < as.X; i++ {
r := as.X / 2
d := math.Sqrt(float64((i-r)*(i-r) + (j-r)*(j-r)))
b := uint8(max(0, min(0xff, 3*0xff-int(d*3*0xff)/r)))
a.SetAlpha(i, j, color.Alpha{b})
}
}
spotLightImage, _ = ebiten.NewImageFromImage(a, ebiten.FilterNearest)
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if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Masking (Ebiten Demo)"); err != nil {
log.Fatal(err)
}
}