SDL - window doesn't show anything

Question

I\'m doing my first steps in SDL (C++) an took some tutorials from the www.

But there is one problem. I have installed SDL2 on my Linux Mint System, compiled the tut

Answer 1

SDL - window doesn't show anything

The reason is that you're not drawing anything. You created a window, a renderer, a surface, and a texture. However you're not drawing anything. And the visual result reflects exactly what you've done.

To simply display a BMP image, load the image into a surface and use SDL_BlitSurface to copy it to the screen. Or to work with textures, you shall draw primitives like triangles or quads just like working with OpenGL.

Also another problem: why your window looks filled with other content than a blank screen?
That's because these years the default video mode is set to double buffering, which means there's a front buffer to be shown and a back buffer to render on. When finishing rendering a single frame, you shall call something like SDL_Flip (seems it's been obsoleted in SDL2) or SDL_UpdateWindowSurface.

EDITED: I've edited your code and here's something that works: (removed renderer/texture, added SDL_BlitSurface and SDL_UpdateWindowSurface)

#ifdef __cplusplus
    #include <cstdlib>
#else
    #include <stdlib.h>
#endif

#include <stdio.h>
#include <SDL2/SDL.h>

#include <iostream>

int main ( int argc, char** argv )
{
    if (SDL_Init(SDL_INIT_EVERYTHING) != 0){
        std::cout << "SDL_Init Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    SDL_Window *win = SDL_CreateWindow("Hello World!", 100, 100, 640, 480,
    SDL_WINDOW_SHOWN);
    if (win == NULL){
        std::cout << "SDL_CreateWindow Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    SDL_Surface *bmp = SDL_LoadBMP("cb.bmp");
    if (bmp == NULL){
        std::cout << "SDL_LoadBMP Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    SDL_BlitSurface(bmp, 0, SDL_GetWindowSurface(win), 0);
    SDL_UpdateWindowSurface(win);

    SDL_Delay(4000);

    SDL_DestroyWindow(win);
    SDL_Quit();

    return 0;
}

Answer 2

Since you're using SDL2, you should not be using an SDL_Surface to update the screen. That's the old way that SDL 1.2 had to use. The new renderer subsystem is what you want for general use because it is hardware-accelerated (uses the GPU) while SDL_BlitSurface() and SDL_UpdateWindowSurface() are not (all pixel copying is done on the CPU).

So here's what to do. Do not use SDL_GetWindowSurface(). Use your previous code for creating a renderer and texture. Replace SDL_BlitSurface() with a call to SDL_RenderCopy(). Replace SDL_UpdateWindowSurface() with a call to SDL_RenderPresent().

Alternatively, you can use SDL_gpu (note: I'm the author), which feels like the older SDL 1.2 blitting API, but has even more features and optimizations than SDL_Renderer.