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# Pong Help

Posts: 8Member
I have gotten a pong program to work but i need help on making it run faster. when the screen refreshes the bottom line blinks because of the slight time it takes to refresh, can that be easily fixed? Problem most likely is ineffiecent loops, but i don't know how to fix.
· ·

• Posts: 6,349Member
: I have gotten a pong program to work but i need help on making it run faster. when the screen refreshes the bottom line blinks because of the slight time it takes to refresh, can that be easily fixed? Problem most likely is ineffiecent loops, but i don't know how to fix.
:
Do not refresh the whole screen, but only the paddles and the ball. This is a lot faster than a whole-screen refresh.
· ·
• Posts: 8Member

: Do not refresh the whole screen, but only the paddles and the ball. This is a lot faster than a whole-screen refresh.
:
how do i do that?
· ·
• Posts: 6,349Member
[b][red]This message was edited by zibadian at 2006-10-15 10:56:26[/red][/b][hr]
:
: : Do not refresh the whole screen, but only the paddles and the ball. This is a lot faster than a whole-screen refresh.
: :
: how do i do that?
:
That greatly depends on the text/graphics. Nearly always it is done by removing the old position and painting it in the new one. Here is a simple example of a 0 moving along a line:
[code]
for i := 1 to 60 do
begin
if i = 1 then
GotoXY(60, 2); write(' '); { remove old location }
else
GotoXY(i-1, 2); write(' '); { remove old location }
GotoXY(i, 2); write('0'); { write the new location }
end;
[/code]
More advanced methods store the old location along with the new one, and update that with each step.

· ·
• Posts: 8Member
i shall try. that just adds a few more vars...one more question, code only works right now so that the entire screen refreshes at once, ei the ball doesn't move unless the paddles move or any other random key is pressed. how can this be fixed? something like adding a timed statement to the major loop? if so, how.
· ·
• Posts: 111Member
I am myself programming an ASCII game that refreshes the screen about 20 times per second. I use the below code, which writes directly to the screen through assembler code, and is thus REALLY fast.

[CODE]
PROCEDURE FastWrite(Const Col, Row, Attr : Byte; Const Str : String); Assembler;
ASM
PUSH DS {Save DS}
MOV DL,CheckSnow {Save CheckSnow Setting}
MOV ES,SegB800 {ES = Colour Screen Segment}
MOV SI,SegB000 {SI = Mono Screen Segment}
MOV DS,Seg0040 {DS = ROM Bios Segment}
MOV BX,[49h] {BL = CRT Mode, BH = ScreenWidth}
MOV AL,Row {AL = Row No}
MUL BH {AX = Row * ScreenWidth}
XOR CH,CH {CH = 0}
MOV CL,Col {CX = Column No}
ADD AX,AX {Multiply by 2 (2 Byte per Position)}
MOV DI,AX {DI = Screen Offset}
CMP BL,7 {CRT Mode = Mono?}
JNE @@DestSet {No - Use Colour Screen Segment}
MOV ES,SI {Yes - ES = Mono Screen Segment}
@@DestSet: {ES:DI = Screen Destination Address}
LDS SI,Str {DS:SI = Source String}
CLD {Move Forward through String}
LODSB {Get Length Byte of String}
MOV CL,AL {CX = Input String Length}
JCXZ @@Done {Exit if Null String}
MOV AH,Attr {AH = Attribute}
OR DL,DL {Test Mono/CheckSnow Flag}
JZ @@FWrite {Snow Checking Disabled or Mono - Use FWrite}
{Output during Screen Retrace's}
MOV DX,003DAh {6845 Status Port}
@@WaitLoop: {Output during Retrace's}
MOV BL,[SI] {Load Next Character into BL}
INC SI {Update Source Pointer}
CLI {Interrupts off}
@@Wait1: {Wait for End of Retrace}
IN AL,DX {Get 6845 status}
TEST AL,8 {Vertical Retrace in Progress?}
JNZ @@Write {Yes - Output Next Char}
SHR AL,1 {Horizontal Retrace in Progress?}
JC @@Wait1 {Yes - Wait until End of Retrace}
@@Wait2: {Wait for Start of Next Retrace}
IN AL,DX {Get 6845 status}
SHR AL,1 {Horizontal Retrace in Progress?}
JNC @@Wait2 {No - Wait until Retrace Starts}
@@Write: {Output Char and Attribute}
MOV AL,BL {Put Char to Write into AL}
STOSW {Store Character and Attribute}
STI {Interrupts On}
LOOP @@WaitLoop {Repeat for Each Character}
JMP @@Done {Exit}
{Ignore Screen Retrace's}
@@FWrite: {Output Ignoring Retrace's}
TEST SI,1 {DS:SI an Even Offset?}
JZ @@Words {Yes - Skip (On Even Boundary)}
LODSB {Get 1st Char}
STOSW {Write 1st Char and Attrib}
DEC CX {Decrement Count}
JCXZ @@Done {Finished if only 1 Char in Str}
@@Words: {DS:SI Now on Word Boundary}
SHR CX,1 {CX = Char Pairs, Set CF if Odd Byte Left}
JZ @@ChkOdd {Skip if No Pairs to Store}
@@Loop: {Loop Outputing 2 Chars per Loop}
MOV BH,AH {BH = Attrib}
XCHG AH,BH {AL = 1st Char, AH = Attrib, BH = 2nd Char}
STOSW {Store 1st Char and Attrib}
MOV AL,BH {AL = 2nd Char}
STOSW {Store 2nd Char and Attrib}
LOOP @@Loop {Repeat for Each Pair of Chars}
@@ChkOdd: {Check for Final Char}
JNC @@Done {Skip if No Odd Char to Display}
LODSB {Get Last Char}
STOSW {Store Last Char and Attribute}
@@Done: {Finished}
POP DS {Restore DS}
END;
[/CODE]

Note that when you use this procedure, the top left coordinate is (0,0). So if you want to write a red 'X' to coordinate 79,20 (the last coordinate on the 21st line), you just write:

FastWrite(79, 20, 12, 'X'); (where 12 is the color)
· ·
• Posts: 6,349Member
: i shall try. that just adds a few more vars...one more question, code only works right now so that the entire screen refreshes at once, ei the ball doesn't move unless the paddles move or any other random key is pressed. how can this be fixed? something like adding a timed statement to the major loop? if so, how.
:
Use the Keypressed() function to detect if there is a keypress. Then you can use ReadKey() to get the key-value.
· ·
• Posts: 8Member
[b][red]This message was edited by acidicburn at 2006-10-15 12:3:38[/red][/b][hr]
: Use the Keypressed() function to detect if there is a keypress. Then you can use ReadKey() to get the key-value.
:thx this should help a lot. So keypressed() detects if a key was pressed. so how would i use it in a program. if keypressed then? also, i don't know any assembly, i just started using pascal about a month ago.

· ·
• Posts: 6,349Member
: [b][red]This message was edited by acidicburn at 2006-10-15 12:3:38[/red][/b][hr]
: : Use the Keypressed() function to detect if there is a keypress. Then you can use ReadKey() to get the key-value.
: :thx this should help a lot. So keypressed() detects if a key was pressed. so how would i use it in a program. if keypressed then? also, i don't know any assembly, i just started using pascal about a month ago.
:
:
:
:
Here's an example, which stops if you press enter:
[code]
var
i: integer;
begin
i := 0;
repeat
GotoXY(1, 1);
write(i);
i := (i+1) mod 999;
if Keypressed then
begin