How to replace invalidate with a function that goes to OnDraw without deleting the screen pictures

Question

Hi this is my first post on stack overflow.
I am using visual studio 2006 with mfc to build a snake game.Im trying to make it so when you press an arrow (left) the snake goes the direction of that arrow (left) until the snakes dies(hits a wall,himself) or the player presses another button.

Now I need some help with going from a function to OnDraw without deleting the stuff on the screen.

Also i want to know, how to make it so that when the program is in a middle of a function that is going call another function and at a point before the other function is called you press a button,the function continues till the moment that the other function is called but does not call the function instead it goes to OnKeyDown?

Answer 1

OnDraw is required to redraw the whole window because that window might have just been uncovered, or un-minimized. If you want to ignore that basic Windows requirement then just make yourself a DrawMore function and use CClientDC to get a DC to use to draw more.

Your other question implies an incorrect design. Do something in response to a message, then return to MFC so it can get keys, mouse, etc. messages. Your program has to be message-driven. To keep things moving along even when there is no keystroke you can use a timer (SetTimer, handle WM_TIMER messages).