SDL: image and drawing something

[cranberry]

I am reloading image time by time to screen SDL_Surface. Then I draw manually some lines to same screen SDL_Surface. The problem is that lines should be top of image, if I reload a new image, lines are hidden. What would be fastest way to refresh lines? Can I use somehow second surface?

The code is something like this:

// Init
screen = SDL_SetVideoMode( systemX, systemY, bpp, SDL_SWSURFACE );

//Loading image
SDL_BlitSurface(imageSurf, NULL, screen, &offset);
SDL_Flip( screen );

// Drawing lines call setPixel function and then update screen
char *position = (char *)screen->pixels;
position += ( screen->pitch * y );
position += ( screen->format->BytesPerPixel * x );
memcpy ( position , &color , screen->format->BytesPerPixel );
...
SDL_Flip( screen );

[ramstrong]

Looks like you have an extra flip. You have image-flip-lines-flip, where you should have image-lines-flip.

[theArtist]

You do not need a second surface.

You could do this:

Code: Select all

//First write the image onto the screen

SDL_BlitSurface(imageSurf, NULL, screen, &offset);

// Drawing lines call setPixel function to write over the screen which already contains the image
char *position = (char *)screen->pixels;
position += ( screen->pitch * y );
position += ( screen->format->BytesPerPixel * x );
memcpy ( position , &color , screen->format->BytesPerPixel );

//Then finally refresh the screen
SDL_Flip(screen);