Bouncing Ball

Write a program that simulates a ball bouncing within a rectangle.

Your rectangle will be the size of the standard MS-DOS screen: 25 rows by 80 columns (X = 0-79, and Y = 0-24). The rectangle should contain an internal vertical wall consisting of a single column of block characters (ASCII code 0DBh) starting at row 5, column 40, extending down to row 19, column 40. The background should be blue, and the wall and ball should be white.

The ball travels at a constant speed, determined by a delay value of 20 milliseconds inside the loop that displays, erases, and moves the ball. The following sequence of actions will be in the loop:

display, delay, erase, move

• The ball is just a single character, drawn with the ASCII code 2. To 'move' the ball, you write over it with a blank, move the cursor position to a new location, and redraw the ball. The ball can only move 1 row and 1 column during each loop cycle.
• You will need to call the following library procedures: Clrscr, Delay, SetTextColor, WriteChar, and Gotoxy.
• You will (probably) need to use the high-level .IF, .ELSE, and .ENDIF directives explained at the end of Chapter 6.

The cursor itself should be invisible. This is accomplished by executing the following 32-bit code:

;----- hides the cursor ----------------------------------------
.data
cursorInfo CONSOLE_CURSOR_INFO <>
outHandle  DWORD ?
.code
   INVOKE GetStdHandle, STD_OUTPUT_HANDLE
   mov    outHandle,eax
   INVOKE GetConsoleCursorInfo, outHandle, ADDR cursorInfo
   mov    cursorInfo.bVisible,0
   INVOKE SetConsoleCursorInfo, outHandle, ADDR cursorInfo
;---------------------------------------------------------------

The Algorithm

Suppose you have a current location (X, Y), and two direction values, dX, and dY. The latter control the ball's movement. For example, if dX =1 and dY = 1, the ball is moving downward and to the right.

Evaluate the potential new X and Y location:

• If the new location is outside the rectangle's X and Y coordinates, reverse the ball's direction by negating dX or dY, whichever is appropriate.
• If the new location is in the middle of the vertical wall, negate dX.
• If the new location is either the top or the bottom of the vertical wall, negate dY.

Next, add dX and dY to your current X and Y coordinates, generating the ball's new location. Redraw the ball at this new location.