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基于视图在父级中的位置呈现位图

android-bitmap android-view android-canvas scale android

Marcin Wróblewski · 技术社区 · 6 年前

我正在做一个简单的图像编辑器。一开始,我认为简单地将视图状态保存为位图是个好主意,但事实证明,屏幕分辨率范围很广,这会导致巨大的质量(和内存使用)波动。

现在,我正在尝试创建一个模块,该模块将视图状态转换为所需的分辨率。

在下面的代码中,我尝试在画布中重新创建视图的当前状态:

    Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.id.test_1_1);
    bitmap = Bitmap.createScaledBitmap(bitmap, parentView.getMeasuredWidth(), parentView.getMeasuredHeight(), true);

    Canvas canvas = new Canvas(bitmap);
    Paint paint = new Paint();
    for (View rootView : addedViews) {
        ImageView imageView = rootView.findViewById(R.id.sticker);

        float[] viewPosition = new float[2];
        transformToAncestor(viewPosition, parentView, imageView);

        Bitmap originalBitmap = ((BitmapDrawable) imageView.getDrawable()).getBitmap();
        Matrix adjustMatrix = new Matrix();
        adjustMatrix.postTranslate(viewPosition[0], viewPosition[1]);
        adjustMatrix.postScale(
                rootView.getScaleX(),
                rootView.getScaleY(),
                rootView.getWidth() / 2,
                rootView.getHeight() / 2);
        adjustMatrix.postRotate(rootView.getRotation(),
                rootView.getWidth() / 2,
                rootView.getHeight() / 2);

        canvas.drawBitmap(originalBitmap, adjustMatrix, paint);
    }

transformToAncestor 函数来自 here .

public static void transformToAncestor(float[] point, final View ancestor, final View descendant) {
    final float scrollX = descendant.getScrollX();
    final float scrollY = descendant.getScrollY();
    final float left = descendant.getLeft();
    final float top = descendant.getTop();
    final float px = descendant.getPivotX();
    final float py = descendant.getPivotY();
    final float tx = descendant.getTranslationX();
    final float ty = descendant.getTranslationY();
    final float sx = descendant.getScaleX();
    final float sy = descendant.getScaleY();

    point[0] = left + px + (point[0] - px) * sx + tx - scrollX;
    point[1] = top + py + (point[1] - py) * sy + ty - scrollY;

    ViewParent parent = descendant.getParent();
    if (descendant != ancestor && parent != ancestor && parent instanceof View) {
        transformToAncestor(point, ancestor, (View) parent);
    }
}

(作者写了一个注释,他的函数不支持旋转,但是在我的例子中没有太多的旋转,所以我认为现在不那么重要)。

我的问题是:

第一个图像是通过保存父视图状态生成的。第二种方法是将视图的位置、旋转和比例转换到画布上。如你所见,在画布上,没有缩放的贴纸被正确定位,但是缩放的贴纸被错误定位。

如何正确定位这些缩放视图?

1 回复 | 直到 6 年前

Marcin Wróblewski 6 年前

我自己解决了这个问题。结果我的解几乎可以,但我没有考虑到我对矩阵的操作 是否更改了原始点的排列 ,所以我的

rootView.getWidth() / 2,
rootView.getHeight() / 2

调用后不再适用于视图中心 Matrix.postScale 或 Matrix.postRotation .

我想:

应用比例 以左上角为轴,
应用旋转 轴位于视图中心。

考虑到这些假设,下面是工作代码:

    // setup variables for sizing and transformation
    float position[] = new float[2];
    transformToAncestor(position, rootView, imageView);
    float desiredRotation = imageView.getRotation();
    float sizeDeltaX = imageView.getMeasuredWidth() / (float) imageBitmap.getWidth();
    float sizeDeltaY = imageView.getMeasuredHeight() / (float) imageBitmap.getHeight();
    float desiredScaleX = imageView.getScaleX() * sizeDeltaX * scaleX;
    float desiredScaleY = imageView.getScaleY() * sizeDeltaY * scaleY;
    float imageViewWidth = imageView.getMeasuredWidth() * imageView.getScaleX();
    float imageViewHeight = imageView.getMeasuredHeight() * imageView.getScaleY();

    float rootViewWidth = rootView.getMeasuredWidth();
    float rootViewHeight = rootView.getMeasuredHeight();
    float percentXPos = position[0] / rootViewWidth;
    float percentYPos = position[1] / rootViewHeight;
    float percentXCenterPos = (position[0] + imageViewWidth/2)
            / rootViewWidth;
    float percentYCenterPos = (position[1] + imageViewHeight/2)
            / rootViewHeight;

    float desiredPositionX = background.getWidth() * percentXPos;
    float desiredPositionY = background.getHeight() * percentYPos;
    float desiredCenterX = background.getWidth() * percentXCenterPos;
    float desiredCenterY = background.getHeight() * percentYCenterPos;

    // apply above variables to matrix
    Matrix matrix = new Matrix();
    float[] points = new float[2];
    matrix.postTranslate(
            desiredPositionX,
            desiredPositionY);

    matrix.mapPoints(points);
    matrix.postScale(
            desiredScaleX,
            desiredScaleY,
            points[0],
            points[1]);

    matrix.postRotate(
            desiredRotation,
            desiredCenterX,
            desiredCenterY);

    // apply matrix to bitmap, then draw it on canvas
    canvas.drawBitmap(imageBitmap, matrix, paint);

如你所见, mapPoints 方法是我问题的答案-它只返回点之后转换。