Lunar Lander - a small tutorial on Perl SDL
+SDL::Tutorial::LunarLander - a small tutorial on Perl SDL
+ +Tutorials
You can see the final version of the demo code by doing:
--
perl -MSDL::Tutorial::LunarLander=lander.pl -e1 ++ + + + + + perl -MSDL::Tutorial::LunarLander=lander.pl -e1 + + + + + +--
this will create all three files used in the tutorial:
+this will create all three files used in the tutorial.
@@ -61,8 +79,13 @@ later. We must build the game logic first! If we start with a simpler simulation, we can worry with the presentation later.So, here's the initial code:
--
#!/usr/bin/perl ++ + + + + + #!/usr/bin/perl use strict; use warnings; @@ -87,11 +110,21 @@ later. print "You landed on the surface safely! :-D\n"; } + + + + + +-
Run the code and you'll see something like this:
--
at 0 s height = 1000 m, velocity = 0 m/s ++ + + + + + at 0 s height = 1000 m, velocity = 0 m/s at 1 s height = 1000 m, velocity = 1 m/s at 2 s height = 999 m, velocity = 2 m/s at 3 s height = 997 m, velocity = 3 m/s @@ -104,8 +137,13 @@ later. CRASH!!! + + + + + +-
"What happened? How do I control the ship???"
So, create add this simple script to the end of your file:
--
__DATA__ ++ + + + + + __DATA__ at 41s, accelerate 10 m/s^2 up at 43s, 10 m/s^2 at 45s, 10 at 47s, 10 at 49s, 10 + + + + + +-
The script is straightforward: it simply states a time when we will push the spaceship up with a given acceleration. It accepts free text: any two numbers you type will work.
We can parse the script using this regular expression:
--
my $script_re = qr/(\d+) \D+ (\d+)/x; ++ + + + + + my $script_re = qr/(\d+) \D+ (\d+)/x; + + + + + +-
And we can build a hash of ( time => acceleration ) with:
--
my %up = map { $_ =~ $script_re } <DATA>; ++ + + + + + my %up = map { $_ =~ $script_re } <DATA>; + + + + + +-
So the middle section of the program will become:
--
my $script_re = qr/(\d+) \D+ (\d+)/x; ++ + + + + + my $script_re = qr/(\d+) \D+ (\d+)/x; my %up = map { $_ =~ $script_re } <DATA>; while ( $height > 0 ) { @@ -161,12 +234,22 @@ free text: any two numbers you type will work. $t = $t + 1; } + + + + + +-
That's it!
Try to run the program, and the ship should land safely:
--
./lunar.pl autopilot.txt ++ + + + + + ./lunar.pl autopilot.txt at 0 s height = 1000 m, velocity = 0 m/s at 1 s height = 1000 m, velocity = 1 m/s at 2 s height = 999 m, velocity = 2 m/s @@ -181,8 +264,13 @@ free text: any two numbers you type will work. You landed on the surface safely! :-D + + + + + +-
Cool, but...
@@ -205,68 +293,107 @@ this tutorial; Save these images in a subdirectory called "images":USING SDL
First step: use the required libraries:
--
use SDL; #needed to get all constants - use SDL::App; - use SDL::Surface; - use SDL::Rect; ++ + + + + + use SDL; #needed to get all constants + use SDL::Video; + use SDL::App; + use SDL::Surface; + use SDL::Rect; + use SDL::Image; + + + + + +-
Second step: initialize
-SDL::App:-
my $app = SDL::App->new( ++ + + + + + my $app = SDL::App->new( -title => "Lunar Lander", -width => 800, -height => 600, -depth => 32, ); + + + + + +-
Third step: load the images and create the necessary "rectangles":
--
my $background = SDL::Surface->new( -name => 'images/background.jpg', ); - my $ship = SDL::Surface->new( -name => 'images/ship.png', ); ++ + + + + + my $background = SDL::Image::load('images/background.jpg'); + my $ship = SDL::Image::load('images/ship.jpg'); + + my $background_rect = SDL::Rect->new(0,0, + $background->w, + $background->h, + ); + + my $ship_rect = SDL::Rect->new(0,0, + $ship->w, + $ship->h, + ); + + + + - my $background_rect = SDL::Rect->new( - -height => $background->height(), - -width => $background->width(), - ); - my $ship_rect = SDL::Rect->new( - -height => $ship->height(), - -width => $ship->width(), - );-
Fourth step: create a sub to draw the spaceship and background:
--
sub draw { - my ( $x, $y ) = @_; # spaceship position ++ + + + + + sub draw { + my ( $x, $y ) = @_; # spaceship position + + # fix $y for screen resolution + $y = 450 * ( 1000 - $y ) / 1000; + + # background + SDL::Video::blit_surface($background, $background_rect, $app, $background_rect ); + + # ship + my $ship_dest_rect = SDL::Rect->new( + $x, $y, $ship->w, $ship->h, + ); + + SDL::Video::blit_surface($ship, $ship_rect, $app, $ship_dest_rect ); + + SDL::Video::update_rects($app, $background_rect); + } + - # fix $y for screen resolution - $y = 450 * ( 1000 - $y ) / 1000; - # background - $background->blit( $background_rect, $app, $background_rect ); - # ship - my $ship_dest_rect = SDL::Rect->new( - -height => $ship->height(), - -width => $ship->width(), - -x => $x, - -y => $y, - ); - $ship->blit( $ship_rect, $app, $ship_dest_rect ); - $app->update($background_rect); - }-
Note that this sub first combines all the bitmaps, using a blit ("Block Image Transfer") operation -- which is quite fast, but does not update the display.
@@ -276,8 +403,13 @@ between cycles ("flickering").Finally, add the following lines to the end of the main loop, so that we call the
-draw()function with the correct spaceship coordinates:-
while ( $height > 0 ) { ++ + + + + + while ( $height > 0 ) { # ... @@ -285,8 +417,13 @@ coordinates: $app->delay(10); } + + + + + +-
That's it!
Run the program and watch the spaceship landing safely on the surface of the moon.