ebiten/examples/rotate/main.go

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// Copyright 2014 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.
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// +build example jsgo
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package main
import (
"bytes"
"image"
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_ "image/jpeg"
"log"
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"math"
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"github.com/hajimehoshi/ebiten"
"github.com/hajimehoshi/ebiten/examples/resources/images"
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)
const (
screenWidth = 320
screenHeight = 240
)
var (
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count = 0
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gophersImage *ebiten.Image
)
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func update(screen *ebiten.Image) error {
count++
if ebiten.IsDrawingSkipped() {
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return nil
}
w, h := gophersImage.Size()
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op := &ebiten.DrawImageOptions{}
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// Move the image's center to the screen's upper-left corner.
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// This is a preparation for rotating. When geometry matrices are applied,
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// the origin point is the upper-left corner.
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op.GeoM.Translate(-float64(w)/2, -float64(h)/2)
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// Rotate the image. As a result, the anchor point of this rotate is
// the center of the image.
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op.GeoM.Rotate(float64(count%360) * 2 * math.Pi / 360)
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// Move the image to the screen's center.
op.GeoM.Translate(screenWidth/2, screenHeight/2)
screen.DrawImage(gophersImage, op)
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return nil
}
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.FilterDefault)
if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Rotate (Ebiten Demo)"); err != nil {
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log.Fatal(err)
}
}