Android开发 TranslateAnimation和ScaleAnimation动画叠加偏移量的计算

目标:在使用TranslateAnimation移动的同时,用ScaleAnimation放大图片,在屏幕居中显示. 看TranslateAnimation的构造方法: TranslateAnimation(float fromXDelta, float toXDelta, float fromYDelta, float toYDelta) 四个参数分别是,动画开始时x座标偏移量,结束时x座标偏移量,开始时y座标偏移量,结束时y座标偏移量,单位像素,有一点搞不懂的是,为什么是float,像素还有半个? 缩放动画 ScaleAnimation(float fromX, float toX, float fromY, float toY) fromX 宽度起始缩放比例,1为原始大小 toX　宽度最终缩放比例 fromY　高度起始缩放比例,1为原始大小 toY 高度最终缩放比例 在TranslateAnimation里,偏移量还要考虑到scale的影响 下面是主要代码:

        //计算activity的size,不包括actionbar
        int activityWidth=findViewById(android.R.id.content).getWidth();
        int activityHeight=findViewById(android.R.id.content).getHeight();
        //获取图片的真实大小
        int[] size=ImageUtils.getBitmapSize(this, R.drawable.wallpaper);
        int bmpWidth=size[0];
        int bmpHeight=size[1];
        //计算目标显示尺寸
        float displayWidth=0;
        float displayHeight=0;
        // 如果图片尺寸比activity的尺寸小,直接原大小显示
        if (activityWidth > bmpWidth && activityHeight > bmpHeight) {
            displayWidth=bmpWidth;
            displayHeight=bmpHeight;
        }else{
            //缩放
            // 计算宽高比
            float target_ratio = (float) activityWidth / activityHeight;
            float real_ratio = bmpWidth / bmpHeight;
            if (real_ratio > target_ratio) {
                // 如果width太大，height太小，以activityWidth为基准
                displayWidth=activityWidth;
                displayHeight=((float)activityWidth/bmpWidth)*bmpHeight;
            } else {
                displayHeight=activityHeight;
                displayWidth=((float)activityHeight/bmpHeight)*bmpWidth;
            }
        }
        //缩放比例,等比例放大,toY=toX
        float toX=displayWidth/imageView.getWidth();

        AnimationSet animationSet = new AnimationSet(true);
        animationSet.setDuration(500);
        animationSet.setInterpolator(new AccelerateInterpolator());

        //计算左上角偏移量,有scale需要乘的1/toX
        float toXDelta=((activityWidth-displayWidth)/2.0f-imageView.getX())*(1/toX);
        float toYDelta=((activityHeight-displayHeight)/2.0f-imageView.getY())*(1/toX);
        //移动
        TranslateAnimation translateAnimation=new TranslateAnimation(0, toXDelta, 0, toYDelta);
        animationSet.addAnimation(translateAnimation);
        
        ScaleAnimation scaleAnimation=new ScaleAnimation(1.0f, toX, 1.0f, toX); 
        animationSet.addAnimation(scaleAnimation);
        animationSet.setFillAfter(true);
        imageView.startAnimation(animationSet);