Relative mouse position of SDL_Surface

In my application I need to return the relative mouse position from an SDL_Surface, the problem is the mouse position that gets returned is relative to the SDL window and not the SDL_Surface. I guess my question is what is the easiest / most effective way of do开发者_开发百科ing this. Any questions just ask. Thanks.

EDIT: Sorry I should have explained better, I have SDL_Surface* Surf_Display; on Surf_display there is an Image say its 1000 x 1000, So in order to see the image on a 600 x 600 window I have a camera that I can move around ( really its the surface that moves not the camera ) for instance to look right of the image I move the surface -1 left if that makes sense. So my problem is when I click my mouse on a part of the surface(image) my mouse returns the position that the mouse compared to where the cursor is in the window, what i'm wanting is so that it returns the position of the cursor compared to where it is on the surface(image) I hope that better explains the situation. Thanks again

Just add(or subtract, depending on how you look at it) the offset to the mouse coordinates. So you're drawing the surface something like this:

SDL_Rect dest_rect = { -camera.x, -camera.y };
SDL_BlitSurface(image_surface, NULL, screen_surface, &dest_rect);

I don't know if you're using event based mouse handling, or if you're using SDL_GetMouseState, but either way, you would simply add camera.x and camera.y to the mouse position, for example:

int x, y;
SDL_GetMouseState(&x, &y);
x += camera.x;
y += camera.y;