Syntactic Confectionery Delight PerlMonks

### "flashing"-like stuff

 on Sep 24, 2011 at 14:54 UTC Need Help??
Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

ok, I'm not talking about neon lights or something :P

I'm writing a small perl clone of PONG -- you know, the game everyone played at least once

this is the code so far:

```#!/usr/bin/perl

\$|=1;

(\$w, \$h) = GetTerminalSize;

\$x1 = 3; \$y1 = 3;
\$dx = 0.05; \$dy = 0.05;

print "\e[H";
print "\n" x (\$h-2); print " " x (\$w/2-5);
print "##########\r";
\$x=(\$w/2-5);

while (1) {

if (\$key eq "d") {\$x++; if (\$x>(\$w-10)) {\$x=(\$w-10)};
print "\e[H"; print "\n" x (\$h-2); print "\r"; pri
+nt "\e[K"; print " " x \$x; print "##########\r";}
if (\$key eq "a") {\$x--; if (\$x<0) {\$x=0};
print "\e[H"; print "\n" x (\$h-2); print "\r"; pri
+nt "\e[K"; print " " x \$x; print "##########\r"; }

print "\e[H";
for (0..(\$h-3)) {print " " x (\$w); print "\n"}
print "\e[H\n\n\n"; print "\n" x \$y1; print "\r\e[K"; print " " x \$x1;
+ print "O\r";

\$x1 = (\$x1 + \$dx);
\$y1 = (\$y1 + \$dy);

if ( (\$y1)>=(\$h-5) || \$y1<=0) {\$dy *= -1}
if ( (\$x1)>=(\$w-1) || \$x1<=0) {\$dx *= -1}

}

yes - there isn't any "my" or strict or warnigns... but that's not the problem. and yes - the ball bounce in its own way, don't caring about the pad

before go ahead, I've got this problem, when you run that code, the cursor of the ball made everything "flashing" and make the game annoying

how can I avoid this annoying flashing ?

Replies are listed 'Best First'.
Re: "flashing"-like stuff
by zentara (Archbishop) on Sep 24, 2011 at 16:55 UTC
how can I avoid this annoying flashing ?

Have you considered using a GUI, a Graphical User Interface, like Tk, Wx, Tkx, Gtk2, etc? Just in case you weren't aware that better ways exit for Pong, than just using a terminal. See PONG with TkZinc for example.

I'm not really a human, but I play one on earth.
Old Perl Programmer Haiku ................... flash japh
oh, thanks, but I was trying to write specifically a ASCII version :)
Re: "flashing"-like stuff
by MidLifeXis (Monsignor) on Sep 25, 2011 at 18:54 UTC

I think that I am reading your code correctly, if not, then ignore as appropriate.

When you are printing your movement, you are first clearing the old location, then writing to the new location. There is a period of time where the screen does not have the "sprite" displayed. With graphics-based sprites, I believe that the correct solution is to xor at the new location, then xor at the old location. In your text based version, print to the new location first, then clear the old location. There may be some edge cases <update>especially when old and new overlap</update> that you need to consider.

It has been a number of years since I have tackled this problem, but I seem to remember it being a common one when moving blocks of stuff around the screen.

--MidLifeXis

I solved this way:
```#!/usr/bin/perl

start:
\$|=1;

(\$w, \$h) = GetTerminalSize;

\$n = 0.97; #AI sternght
\$l = 10; #difficulty

\$x1 = \$w/2; \$y1 = \$h/2;

@dxs = (-0.09, -0.08, -0.07, -0.06, -0.05, 0.05, 0.06, 0.07, 0.08, 0.0
+9);

@d = (0.05, -0.05);
\$dx = \$d[rand @d];
\$dy = \$d[rand @d];

\$x = \$w/2-5;

while (1) {

if (\$key eq "d") {\$x++; \$x = \$w-10 if \$x > \$w-10}
if (\$key eq "a") {\$x--; \$x = 0     if \$x < 0}

\$s = " " x ((\$x1-5)*\$n) . "[========]";
\$s .= "\n" x \$y1 . " " x \$x1 . "o";
\$s .= "\n" x (\$h-\$y1-4) . " " x \$x . "[========]\n\nyou:\t\t\$you\ncomp
+uter:\t\$pc\n\r";
print \$s;

\$dx *= -1 if \$x1 >= \$w-1 || \$x1 <= 0;
\$dy *= -1 if  (\$y1 >= \$h-5 && \$x1 > \$x && \$x1 < \$x+10) || (\$y1 <= 1 &&
+ \$x1 > ((\$x1-5)*\$n) && \$x1 < ((\$x1+5)*\$n));
\$dx = \$dxs[\$x1-\$x] if  (\$y1 >= \$h-5 && \$x1 > \$x && \$x1 < \$x+10) || (\$y
+1 <= 1 && \$x1 > ((\$x1-5)*\$n) && \$x1 < ((\$x1+5)*\$n));

\$x1 += \$dx;
\$y1 += \$dy;

if (\$y1 < 0) {ReadMode 0; ++\$you; sleep 1; goto start}
if (\$y1 > \$h-4) {ReadMode 0; ++\$pc; sleep 1; goto start}

select(undef, undef, undef, 0.005/\$l);
system('clear');

}

saving everything inside \$s (: now it works perfectly (it has some minor bugs, but whatever)
Re: "flashing"-like stuff
by Anonymous Monk on Sep 24, 2011 at 16:18 UTC
here is an udated version, for better readability:
```#!/usr/bin/perl

\$|=1;

(\$w, \$h) = GetTerminalSize; #get size of the screen

\$x1 = 0; \$y1 = 0; #ball start coordinates
\$dx = 0.05; \$dy = 0.05; #increments to the ball coordinates

\$x = 0; #start position of the pad

while (1) {

if (\$key eq "d") {\$x++; \$x = \$w-10 if \$x > \$w-10} #moving the pad to t
+he right
if (\$key eq "a") {\$x--; \$x = 0     if \$x < 0} #moving the pad to the l
+eft

print "\e[H"; print "\n" x (\$h-2); print "\r\e[K"; print " " x \$x; pri
+nt "##########\r\e[H"; #drawing the pad at the bottom of the screen

for (0..(\$h-3)) {print " " x (\$w); print "\n"} #cleaning the screen ab
print "\e[H\n\n\n"; print "\n" x \$y1; print " " x \$x1; print "O\r"; #d
+rawing the ball

\$x1 += \$dx; #update coordinates of the ball
\$y1 += \$dy;

\$dx *= -1 if \$x1 >= \$w-1 || \$x1 <= 0; #if the ball hits the left or ri
+ght wall
\$dy *= -1 if \$y1 <= 0 || ( \$y1 >= \$h-5 && \$x1 > \$x && \$x1 < \$x+10 ); #
+if the ball hits the top wall or the pad

if (\$y1 > \$h-4) {ReadMode 0; die "\nyou lose!\n"} #if the ball doesn't

}

but the problem's still there, somewhere

Create A New User
Node Status?
node history
Node Type: perlquestion [id://927652]
Approved by davies
help
Chatterbox?
 LanX (for people wondering: yes field hockey still exists and is even more popular than Hasslhoff in Germany) [Corion]: LanX: Ah, that explains a lot :) [marto]: Nobody we spoke to in Berlin had a clue who Hasslhoff was [LanX]: the sidekick of this blonde playboy model which was saving lives with her red bathing suit ... (what was her name again ...) [choroba]: Pamela Anderson? [choroba]: erix: I'm proud to be from a nation that also does one thing well [LanX]: ah yes! And he called her Kit and she could talk while a light was going from her left to right eye and back... [erix]: choroba: pretty impressive! :) LanX imagines which nations would be dominating if the winter olympics were invented in East Asia

How do I use this? | Other CB clients
Other Users?
Others imbibing at the Monastery: (10)
As of 2018-02-23 16:35 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?
When it is dark outside I am happiest to see ...

Results (303 votes). Check out past polls.

Notices?