January 2023
Intermediate to advanced
288 pages
6h 6m
Chinese
Content preview from 移动端AI与ML应用开发：基于iOS和Android
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70
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第
4
章
GraphicOverlay
，这是因为之前 Google 示例中的
GraphicOverlay
已直接添加到我的应
用程序中，并且我正在使用我的应用程序的命名空间。你可能有一个不同的命名空间，
所以一定要为你的
GraphicOverlay
使用正确的命名。
我让布局尽可能简单，这样你就可以专注于物体检测的各个方面
—
这样就差不多
了
—
CameraX 的预览，在它之上是一个 GraphicOverlay，你可以在上面绘制边界框。
你稍后会看到更多这样的内容。
4.3.2 GraphicOverlay
类
在布局中，你看到了一个自定义的
GraphicOverlay
类。此类的工作是管理一组图形对
象（由边界框及其标签组成）并将它们绘制在画布上。需要注意的一件事是，你经常会
遇到相机预览（以相机的分辨率）和放置在它上面的画布（以屏幕分辨率）之间的坐标
差异，例如这个案例。因此，你可能还需要进行坐标转换才能在适当位置的预览之上绘
制。你可以在
GraphicOverlay
类中找到绘制，以及在逐帧操作时管理绘制图形性能的
相关代码。表示为图形对象的边界框将被简单地添加到
onDraw
事件中：
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
synchronized (lock) {
updateTransformationIfNeeded();
for (Graphic graphic : graphics) { ...
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