SDL side-scroller scrolls inconsistantly
- by SDLFunTimes
So I'm working on an upgrade from my previous project (that I posted here for code review) this time implementing a repeating background (like what is used on cartoons) so that SDL doesn't have to load really big images for a level.
There's a strange inconsistency in the program, however: the first time the user scrolls all the way to the right 2 less panels are shown than is specified. Going backwards (left) the correct number of panels is shown (that is the panels repeat the number of times specified in the code). After that it appears that going right again (once all the way at the left) the correct number of panels is shown and same going backwards. Here's some selected code and here's a .zip of all my code
constructor:
Game::Game(SDL_Event* event, SDL_Surface* scr, int level_w, int w, int h, int bpp) {
this->event = event;
this->bpp = bpp;
level_width = level_w;
screen = scr;
w_width = w;
w_height = h;
//load images and set rects
background = format_surface("background.jpg");
person = format_surface("person.png");
background_rect_left = background->clip_rect;
background_rect_right = background->clip_rect;
current_background_piece = 1; //we are displaying the first clip
rect_in_view = &background_rect_right;
other_rect = &background_rect_left;
person_rect = person->clip_rect;
background_rect_left.x = 0; background_rect_left.y = 0;
background_rect_right.x = background->w; background_rect_right.y = 0;
person_rect.y = background_rect_left.h - person_rect.h;
person_rect.x = 0;
}
and here's the move method which is probably causing all the trouble:
void Game::move(SDLKey direction) {
if(direction == SDLK_RIGHT) {
if(move_screen(direction)) {
if(!background_reached_right()) {
//move background right
background_rect_left.x += movement_increment;
background_rect_right.x += movement_increment;
if(rect_in_view->x >= 0) {
//move the other rect in to fill the empty space
SDL_Rect* temp;
other_rect->x = -w_width + rect_in_view->x;
temp = rect_in_view;
rect_in_view = other_rect;
other_rect = temp;
current_background_piece++;
std::cout << current_background_piece << std::endl;
}
if(background_overshoots_right()) {
//sees if this next blit is past the surface
//this is used only for re-aligning the rects when
//the end of the screen is reached
background_rect_left.x = 0;
background_rect_right.x = w_width;
}
}
}
else {
//move the person instead
person_rect.x += movement_increment;
if(get_person_right_side() > w_width) {
//person went too far right
person_rect.x = w_width - person_rect.w;
}
}
}
else if(direction == SDLK_LEFT) {
if(move_screen(direction)) {
if(!background_reached_left()) {
//moves background left
background_rect_left.x -= movement_increment;
background_rect_right.x -= movement_increment;
if(rect_in_view->x <= -w_width) {
//swap the rect in view
SDL_Rect* temp;
rect_in_view->x = w_width;
temp = rect_in_view;
rect_in_view = other_rect;
other_rect = temp;
current_background_piece--;
std::cout << current_background_piece << std::endl;
}
if(background_overshoots_left()) {
background_rect_left.x = 0;
background_rect_right.x = w_width;
}
}
}
else {
//move the person instead
person_rect.x -= movement_increment;
if(person_rect.x < 0) {
//person went too far left
person_rect.x = 0;
}
}
}
}
without the rest of the code this doesn't make too much sense. Since there is too much of it I'll upload it here for testing. Anyway does anyone know how I could fix this inconsistency?
