SDL：如何设置 window 的像素大小（拉伸）

Question

I'm making a retro pixel game so I want to make my window a very low resolution (256x256). However when I try to make it fullscreen, the whole window was just rendered top left, while leaving all other areas black.
I want to know a way of globally setting the size of each pixel in a window, in order to let it fit the fullscreen, or, a way of stretching the whole window (or a renderer?) to a specified size(and full screen) while having the (w, h) unchanged in parameter 2 and 3 in SDL_CreateWindow, and also whilst having the sizes proportional (so, if it was a square window, it should be a square window after stretched, not a rect after stretched into a rect displayer).

Answer 1

First, render your game to a 256x256 texture. This gist has an example, I will inline it below.

Next, figure out the correct size and position of your game texture on your actual window, and render the texture there. That will require modifications to the SDL_RenderCopyEx call, as the gist simply renders it stretched to the screen.

#include <iostream>

#ifdef __linux__
#include <SDL2/SDL.h>
#elif defined(_WIN32)
#include <SDL.h>
#endif

const int WIN_WIDTH = 640;
const int WIN_HEIGHT = 480;

int main(int argc, char **argv){
    if (SDL_Init(SDL_INIT_EVERYTHING) != 0){
        std::cerr << "SDL_Init failed: " << SDL_GetError() << "\n";
        return 1;
    }
    SDL_Window *win = SDL_CreateWindow("Rendering to a texture!", SDL_WINDOWPOS_CENTERED,
        SDL_WINDOWPOS_CENTERED, WIN_WIDTH, WIN_HEIGHT, 0);
    SDL_Renderer *renderer = SDL_CreateRenderer(win, -1,
        SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);

    //Put your own bmp image here
    SDL_Surface *bmpSurf = SDL_LoadBMP("../res/image.bmp");
    SDL_Texture *bmpTex = SDL_CreateTextureFromSurface(renderer, bmpSurf);
    SDL_FreeSurface(bmpSurf);

    //Make a target texture to render too
    SDL_Texture *texTarget = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888,
        SDL_TEXTUREACCESS_TARGET, WIN_WIDTH, WIN_HEIGHT);
    
    //Now render to the texture
    SDL_SetRenderTarget(renderer, texTarget);
    SDL_RenderClear(renderer);
    SDL_RenderCopy(renderer, bmpTex, NULL, NULL);
    //Detach the texture
    SDL_SetRenderTarget(renderer, NULL);

    //Now render the texture target to our screen, but upside down
    SDL_RenderClear(renderer);
    SDL_RenderCopyEx(renderer, texTarget, NULL, NULL, 0, NULL, SDL_FLIP_VERTICAL);
    SDL_RenderPresent(renderer);

    SDL_Delay(1000);
    SDL_DestroyTexture(texTarget);
    SDL_DestroyTexture(bmpTex);
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(win);
    SDL_Quit();
    return 0;
}