Android Mapview slows after drawing too much polygon?

Issue

I've this custom class that extends the Overlay that is being added into my mapview. i have just one of this class that adds all my polygon and text into this overlay class. However this results in a very slow mapview. I added a draw integer and tested out that this class will draw 84 times each time the ondraw function is being called. Is there any solution that will help to reduce the loading speed of the mapview? Right now the mapview is very slow, each time i move left right or even zoom will be very slow. looking at the android catlog, it seems to me that overlay class ondraw is being called everysecond? should i be looking at another type of layer instead of using overlay?

@Override
public void draw(Canvas canvas, MapView mapView, boolean shadow) 
{
    shadow=false;
    int numberofdraw= 0;




    //outline 
    Paint paint = new Paint();
    paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    paint.setStrokeWidth(2);
    //paint.setColor(0x10000000);    
    paint.setColor(Color.BLACK); 
    paint.setStyle(Paint.Style.STROKE);
    paint.setAntiAlias(true);
    Point point1_draw = new Point();     

    for (int i =0;i<data.getCustomPolygonList().size();i++)
    {

        CustomPolygon customPolygon= data.getCustomPolygonList().get(i);
        Path path = new Path();
        path.setFillType(Path.FillType.EVEN_ODD);
        for(int n=0;n<customPolygon.getCorrdinateList().size();n++)
        {

            GeoPoint sector1 = new GeoPoint((int)(customPolygon.getCorrdinateList().get(n).getLatitude()*1e6), (int)((customPolygon.getCorrdinateList().get(n).getLongitude())*1e6));
            if(n==0){
                mapView.getProjection().toPixels(sector1, point1_draw);
                path.moveTo(point1_draw.x,point1_draw.y);
            }else
            {
                mapView.getProjection().toPixels(sector1, point1_draw);
                path.lineTo(point1_draw.x,point1_draw.y);
            }
        }

        path.close();
        canvas.drawPath(path, paint);
        numberofdraw++;
        //  canvas.clipPath(path, Op.DIFFERENCE);

    }


    //inside sector color
    for (int i =0;i<data.getCustomPolygonList().size();i++)
    {
        CustomPolygon customPolygon= data.getCustomPolygonList().get(i);
        paint = new Paint();
        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setStrokeWidth(2);
        paint.setColor(0x186666ff);    
        //paint.setColor(customPolygon.getColor()); 
        paint.setStyle(Paint.Style.FILL_AND_STROKE);
        paint.setAntiAlias(true);
        point1_draw = new Point();     
        Path path = new Path();
        path.setFillType(Path.FillType.EVEN_ODD);
        for(int n=0;n<customPolygon.getCorrdinateList().size();n++)
        {

            GeoPoint sector1 = new GeoPoint((int)(customPolygon.getCorrdinateList().get(n).getLatitude()*1e6), (int)((customPolygon.getCorrdinateList().get(n).getLongitude())*1e6));
            if(n==0){
                mapView.getProjection().toPixels(sector1, point1_draw);
                path.moveTo(point1_draw.x,point1_draw.y);
            }else
            {
                mapView.getProjection().toPixels(sector1, point1_draw);
                path.lineTo(point1_draw.x,point1_draw.y);
            }
        }

        path.close();
        numberofdraw++;
        canvas.drawPath(path, paint);

    }



    //inside sector text
    for (int i =0;i<data.getCustomPolygonList().size();i++)
    {
        CustomPolygon customPolygon= data.getCustomPolygonList().get(i);
        TextPaint paintText = new TextPaint();
        Point   point1 = new Point();     
        String text=customPolygon.getName();

        for(int n=0;n<customPolygon.getCorrdinateList().size();n++)
        {
            if(customPolygon.getTextLocation()!=null)
            {
                paintText.setTextSize(24);
                Rect rect = new Rect();
                paintText.getTextBounds(text, 0, text.length(), rect);
                paintText.setTextAlign(Paint.Align.CENTER);

                paintText.setTypeface(Typeface.DEFAULT_BOLD); 

                paintText.setColor(Color.BLACK);

                GeoPoint sector1 = new GeoPoint((int)(customPolygon.getTextLocation().getLatitude()*1e6), (int)((customPolygon.getTextLocation().getLongitude())*1e6));


                mapView.getProjection().toPixels(sector1, point1);

            }
        }

        numberofdraw++;
        canvas.drawText(text, point1.x, point1.y, paintText);
    }



    Log.e(Config.log_id,"draw no. "+    numberofdraw+"");
}

Solution

there are many ways you can improve it, I will suggest you one.

Buffering: For each polygon create a new canvas and a new bitmap

Canvas myBufferCanvas;
Bitmap myBufferBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888);
myBufferCanvas = new Canvas(myBufferBitmap);

Then only call draw when the polygon is change, call the draw with myBufferCanvas and then call drawBitmap on the true canvas.

The advantage of this method is performance, it will be extremely fast! The disadvantage is memory, if you have to many polygons, you can kill the device. Just try reusing them some home and you will be fine. Just remember that you can apply any transformation to your buffered image without redrawing it.

Answered By - Ilya Gazman