如何获取在 SDL2 上使用 SDL_RenderDrawPoint() 绘制的特定像素的颜色？

Question

SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
SDL_RenderDrawPoint(renderer, (window_height / 2) + xxi[i], -yyi[i] + (window_width / 2));
SDL_RenderPresent(renderer);

现在我想得到 xxi[i], yyi[i] 点的颜色。

但我不知道如何获得。

Answer 1

SDL_RenderReadPixels():

/**
 * Read pixels from the current rendering target to an array of pixels.
 *
 * **WARNING**: This is a very slow operation, and should not be used
 * frequently.
 *
 * `pitch` specifies the number of bytes between rows in the destination
 * `pixels` data. This allows you to write to a subrectangle or have padded
 * rows in the destination. Generally, `pitch` should equal the number of
 * pixels per row in the `pixels` data times the number of bytes per pixel,
 * but it might contain additional padding (for example, 24bit RGB Windows
 * Bitmap data pads all rows to multiples of 4 bytes).
 *
 * \param renderer the rendering context
 * \param rect an SDL_Rect structure representing the area to read, or NULL
 *             for the entire render target
 * \param format an SDL_PixelFormatEnum value of the desired format of the
 *               pixel data, or 0 to use the format of the rendering target
 * \param pixels a pointer to the pixel data to copy into
 * \param pitch the pitch of the `pixels` parameter
 * \returns 0 on success or a negative error code on failure; call
 *          SDL_GetError() for more information.
 */
extern DECLSPEC int SDLCALL SDL_RenderReadPixels(SDL_Renderer * renderer,
                                                 const SDL_Rect * rect,
                                                 Uint32 format,
                                                 void *pixels, int pitch);

将 rect 参数的宽度和高度设置为 1 以读取单个像素。