ebiten/examples/clip/main.go

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// Copyright 2020 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.
2021-06-24 14:49:37 +02:00
//go:build example
// +build example
package main
import (
"bytes"
"image"
_ "image/jpeg"
"log"
"math"
"github.com/hajimehoshi/ebiten/v2"
"github.com/hajimehoshi/ebiten/v2/examples/resources/images"
)
const (
screenWidth = 640
screenHeight = 480
)
var (
gophersImage *ebiten.Image
)
type Game struct {
count int
}
func (g *Game) Update() error {
g.count++
return nil
}
func (g *Game) Draw(screen *ebiten.Image) {
w, h := gophersImage.Size()
op := &ebiten.DrawImageOptions{}
// Move the image's center to the screen's upper-left corner.
// This is a preparation for rotating. When geometry matrices are applied,
// the origin point is the upper-left corner.
op.GeoM.Translate(-float64(w)/2, -float64(h)/2)
// Rotate the image. As a result, the anchor point of this rotate is
// the center of the image.
op.GeoM.Rotate(float64(g.count%360) * 2 * math.Pi / 360)
// Move the image to the screen's center.
op.GeoM.Translate(screenWidth/2, screenHeight/2)
// Use SubImage to clip the rendering region.
const size = 60
r := image.Rect(320-size, 240-size, 320+size, 240+size)
screen.SubImage(r).(*ebiten.Image).DrawImage(gophersImage, op)
}
func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
return screenWidth, screenHeight
}
func main() {
// Decode image from a byte slice instead of a file so that
// this example works in any working directory.
// If you want to use a file, there are some options:
// 1) Use os.Open and pass the file to the image decoder.
// This is a very regular way, but doesn't work on browsers.
// 2) Use ebitenutil.OpenFile and pass the file to the image decoder.
// This works even on browsers.
// 3) Use ebitenutil.NewImageFromFile to create an ebiten.Image directly from a file.
// This also works on browsers.
img, _, err := image.Decode(bytes.NewReader(images.Gophers_jpg))
if err != nil {
log.Fatal(err)
}
gophersImage = ebiten.NewImageFromImage(img)
ebiten.SetWindowSize(screenWidth, screenHeight)
ebiten.SetWindowTitle("Clip (Ebiten Demo)")
if err := ebiten.RunGame(&Game{}); err != nil {
log.Fatal(err)
}
}