Camera 預覽變形問題解決

　　最近開發一款自定義相機采集照片的demo，花了一個上午開發了一個在測試機上功能正常的apk連同測試機一起交付（需求方反饋沒有Android設備），然而晚上被喊去說是在華為暢玩某型號上預覽會變形，拍到的圖片邊界都移位了，只要加個班處理一下機型適配的問題。根據開發經驗，防止預覽圖像變形的終極奧義就是保持照相機硬件支持的某個size（每個特定的手機都有其支持的camera分辨率）、屏幕寬高比、界面上SurfaceView的寬高比盡量一致，同時保持拍照圖與預覽圖分辨率一致，拍出來的照片就和預覽看到的相同。

　　下面給出實現代碼：

　　

    private fun getOptimalPreviewSize(sizes: List<Camera.Size>?, w: Int, h: Int): Camera.Size? {
        val ASPECT_TOLERANCE = 0.1
        val targetRatio = h.toDouble() / w

        if (sizes == null) return null

        var optimalSize: Camera.Size? = null
        var minDiff = java.lang.Double.MAX_VALUE

        for (size in sizes) {
            val ratio = size.width.toDouble() / size.height
            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue
            if (Math.abs(size.height - h) < minDiff) {
                optimalSize = size
                minDiff = Math.abs(size.height - h).toDouble()
            }
        }

        if (optimalSize == null) {
            minDiff = java.lang.Double.MAX_VALUE
            for (size in sizes) {
                if (Math.abs(size.height - h) < minDiff) {
                    optimalSize = size
                    minDiff = Math.abs(size.height - h).toDouble()
                }
            }
        }
        return optimalSize
    }

其中第一個參數sizes是camera支持的預覽size列表，第二個是View的寬，第三個是View的高，由於我這里的surfaceview是全屏的，所以傳入的寬和高可以是屏幕的寬和高

下面給出完整代碼：

    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_camera)
        screenWidth = ScreenUtil.getWindowWidth(this)
        screenHeight = ScreenUtil.getWindowHeigh(this)
        camera = Camera.open(Camera.CameraInfo.CAMERA_FACING_BACK)
        surface.holder.addCallback(this)
    }
    
    override fun surfaceChanged(holder: SurfaceHolder?, format: Int, width: Int, height: Int) {
        camera?.setPreviewDisplay(holder)
        camera?.startPreview()
    }

    override fun surfaceDestroyed(holder: SurfaceHolder?) {
    }


    override fun surfaceCreated(holder: SurfaceHolder?) {
        if (camera == null) {
            camera = Camera.open(Camera.CameraInfo.CAMERA_FACING_BACK)
        }
        val parameters = camera?.parameters
        var sizes = parameters!!.supportedPreviewSizes
        var preSize = getOptimalPreviewSize(sizes, screenWidth, screenHeight)
        parameters.setPreviewSize(preSize!!.width, preSize.height)
        //重新給定surfaceView寬高
        surface.resize(preSize.width, preSize.height)
        if (parameters.supportedFocusModes!!.contains(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO)) {
            parameters.focusMode = Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO
        }
        parameters.sceneMode = Camera.Parameters.SCENE_MODE_AUTO
        //保持picturesize與presize一致
        parameters.setPictureSize(preSize.width, preSize.height)
        parameters.previewFormat = ImageFormat.NV21
        camera?.parameters = parameters
        camera?.setPreviewDisplay(holder)
        camera?.startPreview()
    }
    
    
    private fun getOptimalPreviewSize(sizes: List<Camera.Size>?, w: Int, h: Int): Camera.Size? {
        val ASPECT_TOLERANCE = 0.1
        val targetRatio = h.toDouble() / w

        if (sizes == null) return null

        var optimalSize: Camera.Size? = null
        var minDiff = java.lang.Double.MAX_VALUE

        for (size in sizes) {
            val ratio = size.width.toDouble() / size.height
            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue
            if (Math.abs(size.height - h) < minDiff) {
                optimalSize = size
                minDiff = Math.abs(size.height - h).toDouble()
            }
        }

        if (optimalSize == null) {
            minDiff = java.lang.Double.MAX_VALUE
            for (size in sizes) {
                if (Math.abs(size.height - h) < minDiff) {
                    optimalSize = size
                    minDiff = Math.abs(size.height - h).toDouble()
                }
            }
        }
        return optimalSize
    }

    
    override fun onWindowFocusChanged(hasFocus: Boolean) {
        val decorView = [e-mail]
        decorView.systemUiVisibility = (View.SYSTEM_UI_FLAG_LAYOUT_STABLE or View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                or View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                or View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                or View.SYSTEM_UI_FLAG_FULLSCREEN
                or View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY)
    }

    override fun onPause() {
        super.onPause()
        camera?.stopPreview()
    }

    override fun onDestroy() {
        super.onDestroy()
        camera?.setPreviewCallback(null)
        camera?.release()
    }