I'm making a game thats like has auto scrolling like gradius or raden trad. The background updates constantly and makes it look like your moving. I dont know how to do this though since I'm new to game programming. So far i built something that scrolls the level but when i add in the ship and movement controlls it doesn't work.

I know alot of people have done this before but i cant find code or a tutorial that makes sense.

---- code ------------------------------

int map_x = 0;
int map_y = 1490;
int player_x = 200;
int player_y = 1800;
int scroll = 0;
void scroll_screen() {
scroll++;
}
END_OF_FUNCTION(scroll_screen);

int main(int argc, char *argv[])
{
allegro_init();
install_timer();
install_keyboard(); // Initialize keyboard routines
install_sound(DIGI_AUTODETECT, MIDI_AUTODETECT, NULL);
set_color_depth(32); // Set the color depth
set_gfx_mode(GFX_AUTODETECT, 640,480,0,0); // Change our graphics mode to 640x480
MIDI *music;
music = load_midi("midi/level_1.mid");
play_midi(music, 1);

BITMAP* level = load_bitmap("art/level_1.bmp", NULL);

BITMAP* buffer = create_bitmap(640,1919);

BITMAP* player = load_bitmap("art/Ship_TOP.bmp", NULL);

install_int_ex(scroll_screen, BPS_TO_TIMER(60));//Set our BPS

while ( !key[KEY_ESC] ) {
while( scroll > 0 ) {
if ( key[KEY_UP]){
player_y = map_y--;
}
if ( key[KEY_DOWN]){
player_y = map_y++;
}
if ( key[KEY_LEFT] ){
player_x = map_x--;
}
if ( key[KEY_RIGHT] ){
player_x = map_x++;
}
map_y--;
scroll--;
}
draw_sprite(buffer, level, 0,0);
draw_sprite(buffer, player, player_x, player_y);
blit(buffer, screen, 0,map_y,0,0,640,1919);
clear_bitmap(buffer);
}
return 0; // Exit with no errors

i dont know what a parralex background is.

what i want to do is have the map auto scroll like in games like gradius, r-type, radien trad.

blit(buffer, screen, 0,map_y,0,0,640,1919);

should that not be something like:

blit(buffer, screen, map_x,map_y,0,0,640,480);

but in his blitt the blitted image is BIGGER than the screen. this makes no sense.

And the map_x var is not used in his blit.

But as the buffer is the same size as the screen this should be no problem.

Hmm. Sorry. Just had a quick look at the code.

i Would do it like this:

BITMAP* buffer = create_bitmap(640,1919);
BITMAP* temp = create_bitmap(640,480);

blit(buffer, temp, camera_x, camera_y, 0, 0, 640, 480);
draw_sprite(temp, player, player_x, player_y);


blit(temp, screen, 0,0,0,0,640,480);

Everytime the player/ship moves change the player_x, player_y vars.
(make sure player_x is between 0 and 639, player_y between 0 and 479)

To scroll the background change the camera_x or camera_y vars.

Only a small part of the code. Hope this makes things clearer. If not please ask.
I'm tired and to foul to write more

EDIT

yea. Thats why I changed this part of the blit. Makes no sense to blit a 1000+ image to a screen which is only 480 in size. The most parts of the images would not be visable.

Yes, I did oversee this at the first quick look. Sorry.

Christopher, could you go more into what you where talking about in terms of using the camera_x and camera_y method.

ok i thought about what chris said for a while now and i think i understand the whole idea. I put it into a sample program and it seems to work. Thank you very much for posting that code snippet. ill try out that new code you put up just now and see how that goes.