Question

I’m basically a beginner in C++ but was looking into how to update a string that is in a while loop?

Currently every iteration of the loop it writes the text on top of the previous still its basically a blur of white colour.

This is my loop that im testing with:

while(!quit){
    while( SDL_PollEvent( &event ) ){
        switch(event.type){
            case SDL_QUIT: quit = true; break;
            case SDL_MOUSEMOTION: handle_mouse_position();
        }
    }

    SDL_Rect offset;
    offset.x = 400;
    offset.y = 290;

    std::stringstream s;
    s << "Mouse xpos: " << mouseX << " Mouse ypos: " << mouseY;

    font_surface = TTF_RenderText_Solid(font,s.str().c_str(),font_color);
    SDL_BlitSurface(font_surface, NULL, screen, &offset);   

    //Update the screen
    if( SDL_Flip( screen ) == -1 ) {
        return 1;    
    }
}

Is there some way to clear the previous text output and update it each loop so that it will display mouse position clearly?

Answer 1

You can do that redrawing everything each time, or if your background is a solid color, paint a rectangle and draw the text above it.

The second one is more efficient. But if you have a complex scenario it is better to work with layers. First you render the bottom layer, then the second, and so on… By layers I mean, you can have a background() which draws the background and foreground() which, obviously, draws the foreground. So what you will have is something like:

while (main_loop) {
    background();
    foreground();
}

So you can easily handle more complex scenarios.