Smooth endles scrolling background with canvas?

问题

Welcome all

I have a background image and what I want is for it to be moving slowly to the right and when the image has reach the right end of the screen with the end of the left starting side of the image, the image must start again showing the start of the right side, as an infinite horizontal scroll.

How can this be achieved without generating bitmap overflow memory exceptions?

I tryed it drawing two times the bitmap with canvas... but it is not smooth, it is very creepy with jumps and not optimized:

universeBitmap = Bitmap.createScaledBitmap(universeBitmap, sw, sh, false); 

    universeView = new View(this){

        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);

            if (paused==true){
                canvas.drawBitmap(universeBitmap, universeX, 0, null);          
                return;
            }
            long currentTime=System.currentTimeMillis();
            if ((currentTime-lastdrawTime)>100){                    
                if (universeX>sw){
                    universeX=0;
                }
                lastdrawTime=currentTime;
                universeX+=1;
            }
            canvas.drawBitmap(universeBitmap, universeX, 0, null);
            canvas.drawBitmap(universeBitmap, universeX-sw, 0, null);
            invalidate();
        }   
    };

I also tried without invalidating the view each 100ms, but with a thread and a handler, and same result.... creepy non smooth movement:

universeBitmap = Bitmap.createScaledBitmap(universeBitmap, sw, sh, false); 

            universeView = new View(this){

                @Override
                protected void onDraw(Canvas canvas) {
                    super.onDraw(canvas);               
                    canvas.drawBitmap(universeBitmap, universeX, 0, null);
                    canvas.drawBitmap(universeBitmap, universeX-sw, 0, null);
                }   
            };
.
.
.
        Handler handler=new Handler(){
            @Override
            public void handleMessage(Message msg) {
                if (universeX>sw){
                    universeX=0;
                }
                universeView.invalidate();
                universeX+=1;
            }
        };  

.
.
.

     public void run() {
            try {
               while( !backgroundThread.interrupted() ) {
                   synchronized(this){  
                       handler.sendEmptyMessage(0);   
                       wait(100);
                   }    
               }
    }

Thanks

回答1:

assuming you don't want for user to scroll this background by own you may use TranslateAnimation with INFINITE param for repeat mode, it will be smooth. create 2 ImageViews horizontally (or even simple Views and setting Bitmap as background) and move their parent. when first get off the screen remove it and add another on other side. this is for background photo/image filling whole screen, if you have other size background just add more ImageViews to create 2x or more summary length than width of the screen (which can be easly measured on in onCreate or wherever. Just create something like Adapter for background image or even you may tray existing projects/libs usually named smth like HorizontalScrollView with Adapter returning some large numer in getCount, e.g. Integer.MAX_VALUE

about Bitmap errors - note that Adapter don't destroy lost/lefting Views, but use them as next (recreates) - this is convertView in getView(...) method. use ViewHolder pattern and you will use only two Views with single Bitmap setting (same refrence). you may create just once your static background Bitmap in constructor and keep in LruCache preventing from recycle it. every device can handle bitmap with same size as screen

来源：https://stackoverflow.com/questions/28159606/smooth-endles-scrolling-background-with-canvas