SDL_RenderPresent（）不起作用

Question

我正在尝试使用sdl2在窗口中绘制网格。程序运行时，即使被调用SDL_RenderPresent()，有时也无效，导致透明窗口空白。其他时候，程序正在提供正确的输出。

#include "SDL.h"
#include <stdio.h>
#include <stdlib.h>

#define SCREEN_WIDTH 800
#define SCREEN_HEIGHT 600

const SDL_Color BLACK = { .r = 0, .g = 0, .b = 0, .a = 255 };
const SDL_Color WHITE = { .r = 255, .g = 255, .b = 255, .a = 255 };
const SDL_Color GRAY = { .r = 128, .g = 128, .b = 128, .a = 255 };

const SDL_Color RED = { .r = 255, .g = 0, .b = 0, .a = 255 };
const SDL_Color MAROON =  { .r = 128, .g = 0, .b = 0, .a = 255 };

const SDL_Color BLUE = { .r = 0, .g = 0, .b = 255, .a = 255 };
const SDL_Color NAVY = { .r = 0, .g = 0, .b = 128, .a = 255 };

const SDL_Color LIME = { .r = 0, .g = 255, .b = 0, .a = 255 };
const SDL_Color GREEN = { .r = 0, .g = 128, .b = 0, .a = 255 };

const int P_SIZE = 10;

void draw_grid(SDL_Renderer *renderer)
{
    SDL_Color prev;
    SDL_GetRenderDrawColor(renderer, &prev.a, &prev.g, &prev.b, &prev.a);

    SDL_SetRenderDrawColor(renderer, GRAY.r, GRAY.g, GRAY.b, GRAY.a);
    // drawing the axes
    SDL_RenderDrawLine(renderer, SCREEN_WIDTH / 2, 0,
            SCREEN_WIDTH / 2, SCREEN_HEIGHT); // the Y-axis
    SDL_RenderDrawLine(renderer, 0, SCREEN_HEIGHT / 2,
            SCREEN_WIDTH, SCREEN_HEIGHT / 2); // the X-axis

    SDL_SetRenderDrawColor(renderer, BLACK.r, BLACK.g, BLACK.b, BLACK.a);
    // drawing the grid
    for (int i = 0; i <= SCREEN_WIDTH; i += P_SIZE) {
        if (i == SCREEN_WIDTH / 2) {
            continue;
        }
        SDL_RenderDrawLine(renderer, i, 0, i, SCREEN_HEIGHT);
    }
    for (int i = 0; i <= SCREEN_HEIGHT; i += P_SIZE) {
        if (i == SCREEN_HEIGHT / 2) {
            continue;
        }
        SDL_RenderDrawLine(renderer, 0, i, SCREEN_WIDTH, i);
    }
    SDL_SetRenderDrawColor(renderer, prev.a, prev.g, prev.b, prev.a);
}

int main()
{
    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        fprintf(stderr, "\nUnable to initialize SDL: %s\n", SDL_GetError());
        return 1;
    }
    atexit(SDL_Quit);
    SDL_Window *window =
        SDL_CreateWindow("Clipping",
                SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
                SCREEN_WIDTH, SCREEN_HEIGHT,
                SDL_WINDOW_SHOWN
        );
    SDL_Renderer *renderer = SDL_CreateRenderer(window, -1,
            SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
    if (renderer == NULL) {
        fprintf(stderr, "\nRenderer could not be created:%s\n", SDL_GetError());
        return 1;
    }

    SDL_SetRenderDrawColor(renderer, WHITE.r, WHITE.g, WHITE.b, WHITE.a);
    SDL_RenderClear(renderer);
    draw_grid(renderer);
    SDL_RenderPresent(renderer);
    int quit = 0;
    while (!quit) {
        SDL_Event event;
        while (SDL_PollEvent(&event)) {
            switch (event.type) {
            case SDL_QUIT:
                quit = 1;
                break;
            default:
                break;
            }
        }
    }
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    return 0;
}