如何从SurfaceView绘制到Canvas？

Question

我正在努力做一个简单的画家.它看起来像Android有三个独立的Canvas的问题,并给我顺序绘图.

我用SurfaceView它制作了UI ,从中取出了Holder.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    sv = (SurfaceView) findViewById(R.id.sv);
    holder = sv.getHolder();

    holder.addCallback(callback);
}

然后拿了Surface.

@Override
    public void surfaceCreated(SurfaceHolder holder) {
    surface = holder.getSurface();
}

并通过OnTouchListener()绘制点和线的事件.

private void paintStartDot(float x, float y) {
    Canvas canvas = surface.lockCanvas(null);

    canvas.drawPoint(x, y, drawPaint);
    surface.unlockCanvasAndPost(canvas);

    lastX = x;
    lastY = y;
}

private void paintEndDot(float x, float y) {
    Canvas canvas = surface.lockCanvas(null);

    canvas.drawLine(lastX, lastY, x, y, drawPaint);

    surface.unlockCanvasAndPost(canvas);

    lastX = x;
    lastY = y;
}

截屏视频:

https://youtu.be/NNDnzrtMLZI

怎么了？

完整资源来源:https: //github.com/tseglevskiy/canvasdemo1/blob/error/app/src/main/java/ru/jollydroid/canvasdemo1/MainActivity.java

Answer 1

在Canvas这Surface.lockCanvas给你的是不持久的.您调用的那一刻unlockCanvasAndPost,表面缓冲区的内容将被推送到屏幕.每次打电话,lockCanvas你都需要从头开始重绘图片.

如果要以增量方式更新画布,则应保留由Bitmap您更新的"屏幕外" 画布,以响应用户操作.然后将位图绘制到Surface画布上.

private void paintStartDot(float x, float y) {
    if (mBitmap == null) return;  // not ready yet
    Canvas canvas = new Canvas(mBitmap);
    canvas.drawPoint(x, y, drawPaint);

    // draw the bitmap to surface 
    canvas = surface.lockCanvas(null);
    canvas.drawBitmap(mBitmap, 0, 0, null);
    surface.unlockCanvasAndPost(canvas);
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
    // good place to create the Bitmap
    mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config. ARGB_8888);
    // also here we need to transform the old bitmap to new one
}

我不确定你是否真的需要一个SurfaceView.您可以扩展View并覆盖其View.onDraw方法.在这种情况下,请致电view.invalidate()以表明需要重新绘制.

另请参阅:Android View.onDraw()始终具有干净的Canvas