VGA Video Display Generation using FPGAs - Rapid Prototyping of Digital Systems - page 208

can detect color intensity flicker in large regions unless the alternating
checkerboard pattern is used.

10.14 VHDL Graphics Display Design Example
This simple graphics example will generate a ball that bounces up and down on
the screen. As seen in Figure 10.10, in the VGA_BALL project the ball is red
and the background is white. This example requires the VGA_SYNC design
from Section 10.4 to generate the video sync and the pixel address signals. The
pixel_row signal is used to determine the current row and the pixel_column
signal determines the current column. Using the current row and column
addresses, the process Display_Ball generates the red ball on the white
background and produces the ball_on signal which displays the red ball using
the logic in the red, green, and blue equations.

Figure 10.10 Bouncing Ball Video Output.

Ball_X_pos and Ball_y_pos are the current address of the center of the ball.
Size is the size of the square ball.
The process Move_Ball moves the ball a few pixels every vertical sync and
checks for bounces off of the walls. Ball_motion is the number of pixels to
move the ball at each vertical sync clock. The VGA_SYNC core is also used to
generate sync signals and pixel addresses, but is not shown in the code below.

ENTITY ball IS

PORT(

I G L Red, Green, Blue : OUT STD_LOGIC ;

I G L vert_sync_out : IN STD_LOGIC ;

I G L pixel_row, pixel_column : IN STD_LOGIC_VECTOR( 9 DOWNTO 0 ));

END ball;
ARCHITECTURE behavior OF ball IS

-- Video Display Signals

I G L reset, Ball_on, Direction : STD_LOGIC ;

I G L Size : STD_LOGIC_VECTOR ( 9 DOWNTO 0 );

I G L Ball_Y_motion : STD_LOGIC_VECTOR ( 9 DOWNTO 0 );

I G L Ball_Y_pos, Ball_X_pos : STD_LOGIC_VECTOR ( 9 DOWNTO 0 );