Android双指缩放ScaleGestureDetector检测放大因子大图移动到双指中心点ImageView区域中心,Kotlin

发布时间:2024年01月23日

Android双指缩放ScaleGestureDetector检测放大因子大图移动到双指中心点ImageView区域中心,Kotlin

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在?Android双击图片放大移动图中双击点到ImageView区域中心,Kotlin-CSDN博客 基础上,这次使用ScaleGestureDetector检测两根手指的缩放动作,记录两根手指的中心点位置,根据ScaleGestureDetector检测到的缩放因子(系数),放大原图,并移动放大前两根手指中心点在原图的位置移动到放大后区域。

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class MyImageView : AppCompatImageView {
    private var mCenterX = 0f
    private var mCenterY = 0f

    private val mCirclePaint = Paint()

    private var mSrcBmp: Bitmap? = null
    private var mScaleBmp: Bitmap? = null
    private var testIV: ImageView? = null

    //放大系数。
    private var mScaleFactor = 1f

    private var mScaleGestureDetector: ScaleGestureDetector? = null

    private var mCanDrawScaleBmp = false
    private var mCanDrawCircle = false

    constructor(ctx: Context, attrs: AttributeSet) : super(ctx, attrs) {
        mSrcBmp = (drawable as BitmapDrawable).bitmap //mSrcBmp是原始图大小,没有缩放和拉伸的。

        mCirclePaint.style = Paint.Style.STROKE
        mCirclePaint.strokeWidth = 10f
        mCirclePaint.isAntiAlias = true
        mCirclePaint.color = Color.RED

        mScaleGestureDetector = ScaleGestureDetector(ctx, object : ScaleGestureDetector.SimpleOnScaleGestureListener() {
            override fun onScaleEnd(detector: ScaleGestureDetector) {
                super.onScaleEnd(detector)

                if (detector.currentSpan > 50 && detector.timeDelta > 10) {
                    mScaleFactor = detector.scaleFactor
                }
            }

            override fun onScale(detector: ScaleGestureDetector): Boolean {
                //更新两个手指缩放的中心点。
                mCenterX = detector.focusX
                mCenterY = detector.focusY

                return super.onScale(detector)
            }
        })
    }

    fun setTestImageView(iv: ImageView?) {
        testIV = iv
    }

    private fun updateView() {
        this.invalidate()
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        when (event.actionMasked) {
            MotionEvent.ACTION_MOVE -> {
                mScaleGestureDetector?.onTouchEvent(event)
                mCanDrawCircle = true
            }

            MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
                mCanDrawScaleBmp = true //两个手指松开了,可以绘制放大的图。
                mCanDrawCircle = false
            }
        }

        updateView()

        return true
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        if (mCanDrawCircle) {
            canvas.drawCircle(mCenterX, mCenterY, 10f, mCirclePaint)
        }

        if (mCanDrawScaleBmp) {
            myDraw(canvas)
        }
    }

    private fun myDraw(canvas: Canvas) {
        Thread.sleep(1500)

        if (mScaleBmp == null) {
            //创建一次,避免重复创建,提高速度。
            mScaleBmp = Bitmap.createScaledBitmap(
                mSrcBmp!!,
                (this.width * mScaleFactor + 1).toInt(), //注意这里的精度损失,会造成坐标偏移.
                (this.height * mScaleFactor + 1).toInt(),//注意这里的精度损失,会造成坐标偏移.
                true
            )
        }

        val cx = this.width / 2f
        val cy = this.height / 2f

        val matrix = Matrix()
        matrix.setScale(mScaleFactor, mScaleFactor)
        matrix.setTranslate(cx - mCenterX * mScaleFactor, cy - mCenterY * mScaleFactor)
        canvas.drawBitmap(mScaleBmp!!, matrix, null)

        //中心圆圈
        canvas.drawCircle(cx, cy, 40f, mCirclePaint)
    }
}

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两根手指在原图上缩放,红色小圆圈实时处于两根手指的中心点:

5c5b88a3bb2144bba15e5bc451a242a8.png

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cdd57a98a3c84e46bed9d2b91c1baeb8.png

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当两根手指离开屏幕后,然后放大原图,并把原先手指中心点“点中”的原图位置,移动到屏幕中心:

b1c387a14e8e4c3eae1ac5df7d164ef0.png

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Android双击图片放大移动图中双击点到ImageView区域中心,Kotlin-CSDN博客文章浏览阅读663次,点赞14次,收藏17次。需要注意的,因为在xml布局里面特别设置了ImageView的高度为wrap_content,手指在屏幕触点的位置是放大镜里面放大图片后准确圆心位置,但是,如果ImageView设置成match_parent,则因为ImageView里面的Bitmap被缩放(此处Bitmap其实小于ImageView,被拉伸了),拉伸后的Bitmap水平方向坐标与ImageView一直重合,但竖直方向,Bitmap坐标与ImageView不一致,会造成一种现象,手指触点放大镜放大后,水平方向是正确的,但竖直方向有偏移量。https://blog.csdn.net/zhangphil/article/details/135630975

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文章来源:https://blog.csdn.net/zhangphil/article/details/135669388
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