Question

I want to draw the 2000 points which save to data object.

I use the following code:

Bitmap bitmap = Bitmap.createBitmap(2000,100，Config.ARGB_8888);
Canvas canvasTemp=new Canvas(bitmap);
Paint paint=new Paint();
for (int i = 0; i < 2000; i++) {
canvasTemp.drawPoint(i, data.getData(i), paint);
}
   Matrix matrix = new Matrix(); 
    float scaleWidth = ((float) 640 / 2000);   
float scaleHeight = ((float) 480/ 100);   
matrix.postScale(scaleWidth, scaleHeight);   
 Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0,2000, 100, matrix, true);   
canvas.drawBitmap(newbmp, 0, 0, new Paint());

This drawing speed is too slow. It needs about 5 or 6 seconds.

How to make the drawing speed more quickly?

Answer 1

Why not directly paint on the canvas? It saves you creating two (large) bitmaps:

Paint paint=new Paint();
Matrix matrix = new Matrix(); 
float scaleWidth = ((float) 640 / 2000);   
float scaleHeight = ((float) 480/ 100);   
matrix.postScale(scaleWidth, scaleHeight);   
canvast.concat(matrix);
for (int i = 0; i < 2000; i++) {
  canvas.drawPoint(i, data.getData(i), paint);
}

Just use concat() to scale the draw commands of the canvas.

Additional note: Creating new objects (paint, matrix, two large! bitmaps) in the draw method of a View is not recommended. It results in lots of instance creations/deletions, which result in activating the garbage collector (GC) more often, resulting in (huge) performance issues with your application!

Instead, create the paint and matrix object once, in the constructor of your View.