SurfaceView设置放大和缩小

在Android开发中，SurfaceView 是一个用于显示视频、动画或其他需要高性能渲染内容的视图组件。如果你想要实现 SurfaceView 的放大和缩小功能，可以通过以下步骤来实现：

1. 设置缩放比例

首先，你需要定义一个变量来存储当前的缩放比例。

private float scaleFactor = 1.0f;

2. 实现缩放逻辑

你可以通过触摸事件（例如双指缩放）来调整 scaleFactor。

surfaceView.setOnTouchListener(new View.OnTouchListener() {
    private float startX, startY;
    private float startDistance;

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
                startX = event.getX();
                startY = event.getY();
                break;
            case MotionEvent.ACTION_POINTER_DOWN:
                startDistance = getDistance(event);
                break;
            case MotionEvent.ACTION_MOVE:
                if (event.getPointerCount() == 2) {
                    float currentDistance = getDistance(event);
                    scaleFactor *= currentDistance / startDistance;
                    startDistance = currentDistance;
                    applyScale();
                }
                break;
        }
        return true;
    }

    private float getDistance(MotionEvent event) {
        float dx = event.getX(0) - event.getX(1);
        float dy = event.getY(0) - event.getY(1);
        return (float) Math.sqrt(dx * dx + dy * dy);
    }

    private void applyScale() {
        // Apply the scale factor to your SurfaceView or its contents
        // For example, if you have a Bitmap displayed in the SurfaceView:
        // bitmap = Bitmap.createScaledBitmap(bitmap, (int) (bitmap.getWidth() * scaleFactor), (int) (bitmap.getHeight() * scaleFactor), true);
        // Then redraw the SurfaceView
        surfaceView.invalidate();
    }
});

3. 应用缩放

在 applyScale() 方法中，你需要根据 scaleFactor 来调整 SurfaceView 或其内容的大小。如果你直接在 SurfaceView 上绘制内容，你可能需要重写 onDraw() 方法并应用缩放。

4. 注意事项

性能考虑：频繁的缩放操作可能会影响性能，特别是在处理视频或复杂动画时。
边界检查：确保缩放后的内容不会超出屏幕边界或变得太小而无法识别。
平滑过渡：可以考虑添加动画效果来平滑缩放过程。

示例代码

以下是一个简单的示例，展示了如何在 SurfaceView 上实现基本的缩放功能：

public class ZoomableSurfaceView extends SurfaceView {
    private float scaleFactor = 1.0f;

    public ZoomableSurfaceView(Context context) {
        super(context);
        init();
    }

    public ZoomableSurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        setOnTouchListener(new OnTouchListener() {
            private float startX, startY;
            private float startDistance;

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getActionMasked()) {
                    case MotionEvent.ACTION_DOWN:
                        startX = event.getX();
                        startY = event.getY();
                        break;
                    case MotionEvent.ACTION_POINTER_DOWN:
                        startDistance = getDistance(event);
                        break;
                    case MotionEvent.ACTION_MOVE:
                        if (event.getPointerCount() == 2) {
                            float currentDistance = getDistance(event);
                            scaleFactor *= currentDistance / startDistance;
                            startDistance = currentDistance;
                            applyScale();
                        }
                        break;
                }
                return true;
            }

            private float getDistance(MotionEvent event) {
                float dx = event.getX(0) - event.getX(1);
                float dy = event.getY(0) - event.getY(1);
                return (float) Math.sqrt(dx * dx + dy * dy);
            }

            private void applyScale() {
                invalidate();
            }
        });
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // Apply the scale factor to the canvas
        canvas.save();
        canvas.scale(scaleFactor, scaleFactor);
        // Draw your content here
        // For example, draw a bitmap
        // canvas.drawBitmap(bitmap, 0, 0, null);
        canvas.restore();
    }
}

在这个示例中，ZoomableSurfaceView 类继承自 SurfaceView 并添加了触摸事件处理和缩放逻辑。你可以根据需要进一步扩展和优化这个类。