kotlin音视频系列使用SurfaceView绘制一张图片

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <SurfaceView
        android:id="@+id/mSurfaceView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

/**
 * A client may implement this interface to receive information about
 * changes to the surface.  When used with a {@link SurfaceView}, the
 * Surface being held is only available between calls to
 * {@link #surfaceCreated(SurfaceHolder)} and
 * {@link #surfaceDestroyed(SurfaceHolder)}.  The Callback is set with
 * {@link SurfaceHolder#addCallback SurfaceHolder.addCallback} method.
 */
public interface Callback {
    /**
     * This is called immediately after the surface is first created.
     * Implementations of this should start up whatever rendering code
     * they desire.  Note that only one thread can ever draw into
     * a {@link Surface}, so you should not draw into the Surface here
     * if your normal rendering will be in another thread.
     *
     * @param holder The SurfaceHolder whose surface is being created.
     */
     //大概意思是讲当surface第一次被创建的时候会立马回调这个方法，可以在这里初始化一些你所需要的东西渲染代码。
     //而需要注意的是只有一条线程可以在surface上绘制，想渲染绘制应该是在其他的线程。您的正常渲染将在另一个线程中
    public void surfaceCreated(SurfaceHolder holder);

    /**
     * This is called immediately after any structural changes (format or
     * size) have been made to the surface.  You should at this point update
     * the imagery in the surface.  This method is always called at least
     * once, after {@link #surfaceCreated}.
     *
     * @param holder The SurfaceHolder whose surface has changed.
     * @param format The new PixelFormat of the surface.
     * @param width The new width of the surface.
     * @param height The new height of the surface.
     */
     //作用于surface在任何结构（格式或者尺寸）的变化，都会立马回调这个方法。就是在这个点去更新图像。
     //这个方法总是至少被调用一次。换句话说就是可能会被调用多次。
    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height);

    /**
     * This is called immediately before a surface is being destroyed. After
     * returning from this call, you should no longer try to access this
     * surface.  If you have a rendering thread that directly accesses
     * the surface, you must ensure that thread is no longer touching the
     * Surface before returning from this function.
     *
     * @param holder The SurfaceHolder whose surface is being destroyed.
     */
     //当surface即将销毁的时候，会立马回调此方法。在这个时候你应该过多的再去使用Surface。
     //如果你有一个正在执行渲染的线程。当这个方法返回之前，你应该确保这个线程再也不会去接触这个Surface了
    public void surfaceDestroyed(SurfaceHolder holder);
}

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        mSurfaceView.holder.addCallback(object : SurfaceHolder.Callback {
            override fun surfaceCreated(holder: SurfaceHolder?) {
                Thread {
                    if (holder != null) {
                         //初始化画笔
                        var mypaint = Paint()
                        //抗锯齿
                        mypaint.isAntiAlias = true
                        //锁定画布
                        var canvas = holder.lockCanvas()
                        //获取一张图片
                        var bitmap =BitmapFactory.decodeResource(resources, R.mipmap.ic_launcher_round)
                        if (bitmap != null) {
                            //在画布上把图片绘制上去
                            canvas.drawBitmap(bitmap, Matrix(), mypaint)
                        }
                        //解锁画布
                        holder.unlockCanvasAndPost(canvas)
                    }
                }.start()
            }
            override fun surfaceChanged(holder: SurfaceHolder?, format: Int, width: Int, height: Int) {
            }
            override fun surfaceDestroyed(holder: SurfaceHolder?) {
            }
        })
    }
}