Thread: problem in allegro with sprite leaving trail

Code:

void flip_page(BITMAP* page1, BITMAP* page2, BITMAP* page3, BITMAP* active_page)
{
	if(active_page == page1)
        active_page = page2;
    if(active_page == page2)
        active_page = page3;
	if(active_page == page3)
		active_page = page1;
}
END_OF_FUNCTION(flip_page);

I'm not an allegro programmer but usually with graphics programming setting something with a value, which is what this flip func looks like it is doing, doesn't relate to results on the screen. You must purposely and explicitly set these values to be shown on the screen. Maybe there's a BLIT function in Allegro or DRAW or SET functions or just any function that explicitly sets the new values to screen results. You can't just change the values.

Now that I really think about it, moi you seem very correct. When I get home from school in about 45 minutes I'll test it out. I'll let you know what happens.

Ok here is the latest code. There is still flicker with this. Now, what I need to fix is the if statements that decide which page to clear. See, I don't want to clear a page right before I display it or you get flickering. So now there is a trail left behind, which I can eliminate by clearing each page each time through the loop. But I should NOT have to clear each one. Look at when I call clean_page, and perhaps the clean_page function. I thought I would do the same fix to the clean_page function as I did to the flip_page, but I get compile errors. I'll post that up later....I have to cut grass now.

Code:

#include <allegro.h> // You must include the Allegro Header file

void increase_speed();
void init_all();
void clean_all();
void clean_bitmap(BITMAP *page);
void flip_page(int *wPage, BITMAP* page1, BITMAP* page2, BITMAP* page3, BITMAP** active_page);

volatile long speed_counter = 0;//A long integer which will store the value of the speed counter.

int main(int argc, char *argv[])
{
	allegro_init(); // Initialize Allegro
	install_keyboard(); // Initialize keyboard routines
	set_color_depth(16); // Set the color depth						
	set_gfx_mode(GFX_AUTODETECT, 640,480,0,0); // Change our graphics mode to 640x480

	install_timer();
	LOCK_VARIABLE(speed_counter);
	LOCK_FUNCTION(increase_speed);
	install_int_ex(increase_speed, BPS_TO_TIMER(150));//Set our BPS

	BITMAP *ship, *page1, *page2, *page3, *active_page, *background, *bullet; 

	page1      = create_video_bitmap(SCREEN_W, SCREEN_H);
    page2      = create_video_bitmap(SCREEN_W, SCREEN_H);
    page3      = create_video_bitmap(SCREEN_W, SCREEN_H);
	background = load_bitmap("lee.bmp", NULL);
    ship       = load_bitmap("ship.bmp", NULL); // Load our picture

    clean_bitmap(page1);
    clean_bitmap(page2);
	clean_bitmap(page3);

    active_page    = page1;

	int x          = 0;
	int y          = 0;
	int wPage      = 1; //what page are we on?
	bool validness = true;

/*///////////////////////////////////////////////////////////////////////////////////*/
/*////// Name: Main Loop ////////////////////////////////////////////////////////////*/
/*///////////////////////////////////////////////////////////////////////////////////*/

	while(!key[KEY_ESC])
	{
		while(speed_counter > 0)
		{
		    validness = true;

			if(key[KEY_UP] && key[KEY_RIGHT])
			{
				y--;// Moving down, so up the Y coordinate by 1
				x++;
			    if(y < 0)
			    {
				    y++;
			    }
				if(x > 604)
				{
					x--;
				}
			}
			else if(key[KEY_UP] && key[KEY_LEFT])
			{
				y--;// Moving down, so up the Y coordinate by 1
				x--;
			    if(y < 0)
			    {
				    y++;
			    }
				if(x < 0)
				{
					x++;
				}
			}
			else if(key[KEY_DOWN] && key[KEY_LEFT])
			{
				y++;// Moving down, so up the Y coordinate by 1
				x--;
			    if(y > 440)
			    {
				    y--;
			    }
				if(x < 0)
				{
					x++;
				}
			}
			else if(key[KEY_DOWN] && key[KEY_RIGHT])
			{
				y++;// Moving down, so up the Y coordinate by 1
				x++;
			    if(y > 440)
			    {
				    y--;
			    }
				if(x > 604)
				{
					x--;
				}
			}
		    else if(key[KEY_RIGHT])
		    {
			    x++;// Moving right so up the X coordinate by 1
			    if(x > 604)
		    	{
		    		validness = false;
			    	x--;
			    }
		    }
		    else if(key[KEY_LEFT])// Ditto' - only for left key
		    {
			    x--;// Moving left, so lower the X coordinate by 1
			    if(x < 0)
			    {
				    validness = false;
				    x++;
			    }
		    }
		    else if(key[KEY_UP])// If the user hits the up key, change the picture's Y coordinate
		    {
			    y--;// Moving up, so lower the Y coordinate by 1
			    if(y < 0)
			    {
				    validness = false;
				    y++;
			    }
		    }
		    else if(key[KEY_DOWN])// Ditto' - only for down
		    {
			    y++;// Moving down, so up the Y coordinate by 1
			    if(y > 440)
			    {
				    validness = false;
				    y--;
			    }
		    }

			speed_counter--;
		};
	
		if(validness == true)
		{
		    acquire_screen();// Get the screen

		    masked_blit(ship, active_page, 0,0, x, y,640,480);
            show_video_bitmap(active_page);

			flip_page(&wPage, page1, page2, page3, &active_page);

			if(wPage == 2)
			    clean_bitmap(page3);
			if(wPage == 3)
                clean_bitmap(page1);
			if(wPage == 1)
			    clean_bitmap(page2);

		    release_screen();// Release it
		}
	};


	destroy_bitmap(ship);//Release the bitmap data
	destroy_bitmap(background);
	destroy_bitmap(page1);
	destroy_bitmap(page2);
	destroy_bitmap(page3);
	destroy_bitmap(bullet);

	return(0);// Exit with no errors
}
END_OF_MAIN(); // This must be called right after the closing bracket of your MAIN function.
               // It is Allegro specific.
void increase_speed()
{
	speed_counter++;
}
END_OF_FUNCTION(increase_speed);

void clean_bitmap(BITMAP *page)
{
	acquire_bitmap(page);
    clear_bitmap(page);
    release_bitmap(page);
}
END_OF_FUNCTION(clear_bitmap);

void flip_page(int *wPage, BITMAP* page1, BITMAP* page2, BITMAP* page3, BITMAP** active_page)
{
	if(*active_page == page1)
	{
        *active_page = page2;
		*wPage       = 2;
	}
    if(*active_page == page2)
	{
        *active_page = page3;
		*wPage       = 3;
	}
	if(*active_page == page3)
	{
		*active_page = page1;
		*wPage       = 1;
	}
}
END_OF_FUNCTION(flip_page);