c - 为什么在 SDL 中渲染纹理时会出现虚假的白色像素？

Question

我正在使用 SDL2 在屏幕上绘制一些东西。这是一些代码：

#include <SDL.h>

void main()
{
    SDL_Init(SDL_INIT_EVERYTHING);

    SDL_Window *window = SDL_CreateWindow("Test", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 500, 500, 0);

    SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, 0);

    SDL_Texture *texture;
    {
        SDL_Surface *window_surface = SDL_GetWindowSurface(window);
        Uint32 pixel_format = window_surface->format->format;
        SDL_Surface *surface = SDL_CreateRGBSurfaceWithFormat(0, 48, 48, 8, pixel_format);
        texture = SDL_CreateTextureFromSurface(renderer, surface);
        SDL_FreeSurface(surface);
        SDL_FreeSurface(window_surface);
    }

    SDL_Rect target_rectangle;
    target_rectangle.x = 100;
    target_rectangle.y = 100;
    target_rectangle.w = 48;
    target_rectangle.h = 48;

    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
    SDL_RenderDrawLine(renderer, 0, 50, 50, 0);

    SDL_RenderCopy(renderer, texture, 0, &target_rectangle);

    SDL_RenderPresent(renderer);
        
    SDL_Event event;
    while(1)
    {
        while (SDL_PollEvent(&event))
        {
            switch (event.type)
            {
                case SDL_QUIT:
                return;
                break;
            }
        }

        SDL_Delay(10);
    }
}

该代码创建了一些虚拟的空白纹理texture。对于从位图文件加载的纹理，我得到了相同的行为。这些行是重要的：

SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
SDL_RenderDrawLine(renderer, 0, 50, 50, 0);

SDL_RenderCopy(renderer, texture, 0, &target_rectangle);

SDL_RenderPresent(renderer);

所以在白色像素的某处画一条线，然后将虚拟纹理复制到屏幕上，并将其全部显示出来。当我这样做时，我在纹理的右下角得到一个白色像素。

正如我所说，当纹理来自使用如下代码的位图时，我也会得到这个：

SDL_Surface *bitmap_surface = SDL_LoadBMP("test.bmp");
SDL_Texture *texture = SDL_CreateTextureFromSurface(renderer, bitmap_surface);
SDL_FreeSurface(bitmap_surface);

标签： cgraphicssdl-2game-development