Allegro, sprites leaving trail - allegro

Question

I'm getting the problem my sprites leave a trail behind when i move them.
Tried drawning a BG with every refresh but then it start flickering.
This is what i do
// ...
int main(int argc, char *argv[])
{
BITMAP *buffer = NULL;
BITMAP *graphics = NULL;
buffer = create_bitmap(SCREEN_W, SCREEN_H);
graphics = load_bitmap("my_graphics.bmp", NULL);
clear_to_color(screen, makecol(0, 0, 0));
clear_to_color(buffer, makecol(0, 0, 0));
while(!key[KEY_ESC])
{
// ...
render_map(100,100);
// ...
}
}
void render_map(int w, int h)
{
// ...
for(int i=0;i < w * h;i++)
{
masked_blit(graphics, buffer, 0, 0, pos_x, pos_y, 32, 32);
}
// ...
blit(buffer, screen, camera_x,camera_y,0,0,SCREEN_W, SCREEN_H);
clear_to_color(buffer, makecol(0, 0, 0));
}
Thanks in advance for any help

Answer 1

Your code is a little hard to read, and you've left out big pieces of it. So it's hard to say for sure, but this line looks suspicious:
blit(buffer, screen, camera_x,camera_y,0,0,SCREEN_W, SCREEN_H);
When using a buffer, you typically will always be calling it like:
blit(buffer, screen, 0,0, 0,0, SCREEN_W,SCREEN_H);
and that is the only time you ever draw to the screen. So the steps are:
clear the buffer (by drawing a background image, tileset, color, etc)
draw everything to the buffer
copy the buffer to the screen
repeat