在SDL_Surface像素上绘制一个矩形

Question

我正在尝试弄清楚如何在锁定unsigned char的{​​{1}}成员的pixels像素阵列上绘制彩色矩形。

以下功能应该是前者：

SDL_Surface

它可以工作，但是在通过使用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); } 将修改后的曲面转换为纹理并将纹理复制到屏幕来测试它时，它只显示一个绿色像素：

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，因为我将2D值映射到单维值。它有助于在纸上起草想法。

以下是代码：

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);
}