Question

When dragging a rectangular bitmap on android, I draw the bitmap using this as per tons of example

//short cut code, after getting the new position from event
int x = event.x;
int y = event.y;
canvas.drawRect(bitmap, x - bitmapwidth/2,y-bitmapheight/2,null)

but this has some problem, if you have a wide bitmap and you happen to touch the left part
of the bitmap, the bitmap gets centered around the new touch coordinate from event.

is there a way to drag the bitmap and keeping the position relative to the drag point? just like how mouse drag behaves?

thanks

Answer 1

As for as I understand, you wish to drag a bitmap relative to the starting point when the finger touched down?

This code should do the trick (if that is the case):

boolean startCoordinatesDefined;
Integer xStart;
Integer yStart;

if(touchdown) {
if(startCoordinatesDefined == false) {
startCoordinatesDefined = true;
xStart = event.x;
yStart = event.y;
}
canvas.drawRect(bitmap, event.x - xStart - bitmapwidth/2, event.y - yStart - bitmapheight/2, null);
}
else {
startCoordinatesDefined = false;
xStart = null;
yStart = null;
}