在SDL_Surface像素上绘制矩形

Question

我想弄清楚如何在SDL_Surface的pixels成员上铸造的unsigned char像素数组上绘制彩色矩形。

下面的函数是应该做前：

void draw_rectangle(SDL_Surface* surface, int x, int y, int width, int height) 
{ 
    SDL_LockSurface(surface); 
    //Make each pixel black 
    std::vector<uint8_t> pixels(surface->h * surface->pitch, 0); 

    for (int dy = y; dy < height; dy++) { 
     for (int dx = x; dx < width; dx++) { 
      pixels[dx + dy] = 0; 
      pixels[dx + dy + 1] = 255; 
      pixels[dx + dy + 2] = 0; 
     } 
    } 
    memcpy(surface->pixels, pixels.data(), surface->pitch * surface->h); 
    SDL_UnlockSurface(surface); 
} 

它的工作原理，但通过使用SDL_CreateTextureFromSurface纹理修饰表面转换成一个纹理，然后复制到屏幕上测试时，它仅显示一个绿色像素：

Answer 1

我已经意识到我的指针运算是错误的，我需要考虑垂直偏移，因为我绘制2D值的单维v alues。它有助于在纸上草拟想法。

下面的代码：

void draw_rectangle(SDL_Surface* surface, int x, int y, int width, int height) 
{ 
    SDL_LockSurface(surface); 
    std::vector<uint8_t> pixels(surface->h * surface->pitch, 0); 

    int dy, dx; 
    int maxwidth = width * 3; 
    for (dy = y; dy < height; dy++) { 
     for (dx = x; dx < maxwidth; dx += 3) { 
      pixels[dx + (dy * surface->pitch)] = 0; 
      pixels[dx + (dy * surface->pitch) + 1] = 255; 
      pixels[dx + (dy * surface->pitch) + 2] = 0; 
     } 
    } 
    memcpy(surface->pixels, pixels.data(), surface->pitch * surface->h); 

    SDL_UnlockSurface(surface); 
}