I already asked a dragging question, but didn't ask about not leaving a trail of smudged pixels.
For anyone curious,
This is the stack overflow page i'm using for my Pygame mouse select, mouse-down and drag.
My strategy for smooth dragging over existing pieces is...
On a piece select,
1) paste a blank square over that piece, to clear its start off space,
2) Remember the x,y click displacement from the top left of the piece square, to help maintain the location of the piece as it is dragged under the cursor.
2) Capture the region under the mouse cursor to be repasted once the piece is dragged to cover up the old piece image. Can I save and re-paste the entire screen, super fast way? Redraw would be 2 slow.
Is the double buffing automatic? SetActivePage? setVisualPage()?