如何覆盖onDraw,以获取将要绘制的内容(作为位图)并进行转换? [英] How can I override onDraw so that I take what would have been drawn (as a bitmap) and transform it?
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问题描述
下面的方法有效,但不幸的是,该方法涉及到创建整个屏幕大小的位图-而不仅仅是绘制区域.如果我使用它来绘制UI元素,则会为每个UI元素重新绘制 .这样可以更有效吗?
The method below works, but it unfortunately, this method involves creating a bitmap the size of the entire screen - not just the area that is drawn to. If I use this to draw UI elements, it is redrawn for each UI element. Can this be done more efficiently?
@Override
protected void onDraw(Canvas canvas) {
//TODO: Reduce the burden from multiple drawing
Bitmap bitmap=Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Config.ARGB_8888);
Canvas offscreen=new Canvas(bitmap);
super.onDraw(offscreen);
//Then draw onscreen
Paint p=new Paint();
p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN));
canvas.drawBitmap(bitmap, 0, 0, p);
}
推荐答案
以下代码将更加高效.
public class MyView extends TextView{
private Canvas offscreen;
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyView(Context context) {
super(context);
}
@Override
protected void onDraw(Canvas canvas) {
//We want the superclass to draw directly to the offscreen canvas so that we don't get an infinitely deep recursive call
if(canvas==offscreen){
super.onDraw(offscreen);
}
else{
//Our offscreen image uses the dimensions of the view rather than the canvas
Bitmap bitmap=Bitmap.createBitmap(getWidth(), getHeight(), Config.ARGB_8888);
offscreen=new Canvas(bitmap);
super.draw(offscreen);
//Create paint to draw effect
Paint p=new Paint();
p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN));
//Draw on the canvas. Fortunately, this class uses relative coordinates so that we don't have to worry about where this View is actually positioned.
canvas.drawBitmap(bitmap, 0, 0, p);
}
}
}
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