Question

我正在尝试制作一个SDL图像转换器来制作黑白图像。到目前为止，我的代码运行正常，它从文件位置加载了一个图像，我需要做的只是在灰度转换中，这里是黑白转换代码：

int x = 0;
int y = 0;
Uint32 pixel = pixels[y * image->w + x];

for (int y = 0; y++ < image->h; y++)
   {
    for (int x = 0; x < image->w; x++)

    Uint32 *pixel = (Uint32*)image->pixels
    Uint8 r=0,g=0,b=0;
    SDL_GetRBG(image->&r,&g,&b);
    Uint8 v = 0.212671f * r + 0.715160f * g + 0.072169f * b;
    Uint32 pixel = SDL_MapRGB(image->format,v,v,v);
    pixels[y * image->w + x] = pixel;

   }

我收到以下错误：

SDL.c:73:3: error: expected expression
                Uint32 *pixel = (Uint32*)image->pixels

SDL.c:75:3: warning: implicit declaration of function 'SDL_GetRBG' is invalid in C99 [-Wimplicit-function-declaration]
                SDL_GetRBG(image->&r,&g,&b);

SDL.c:75:21: error: expected identifier
                SDL_GetRBG(image->&r,&g,&b);
                                  ^
SDL.c:75:22: error: use of undeclared identifier 'r'
                SDL_GetRBG(image->&r,&g,&b);

SDL.c:76:25: error: use of undeclared identifier 'r'
                Uint8 v = 0.212671f * r + 0.715160f * g + 0.072169f * b;

SDL.c:76:41: error: use of undeclared identifier 'g'
                Uint8 v = 0.212671f * r + 0.715160f * g + 0.072169f * b;

SDL.c:76:41: error: use of undeclared identifier 'g'
                Uint8 v = 0.212671f * r + 0.715160f * g + 0.072169f * b;

SDL.c:76:41: error: use of undeclared identifier 'g'
                Uint8 v = 0.212671f * r + 0.715160f * g + 0.072169f * b;

Answer 1

以下似乎是发布的代码试图完成的内容

// this assumes the transparancy byte is the high order byte
int x = 0;
int y = 0;

Uint32 *pPixel;
Uint8   transparancy;
Uint8   r;
Uint8   g;
Uint8   b;
Uint8   gray;

for (int y = 0; y < image->h; y++)
{
    for (int x = 0; x < image->w; x++)
    {
        // get address of pixel
        pPixel = &(image->pixels[y][x]);

        // extract individual color values
        // may want to use the factors: 0.212671f, 0.715160f, 0.072169f
        // rather than the following simple shift+and
        transparancy = (*pPixel >>24)&0xFF;
        r = (*pPixel >>16)&0xFF;
        g = (*pPixel >> 8)&0xFF;
        b = (*pPixel >> 0)&0xFF;

        // calculate gray value
        gray = (Uint8)( (Uint32)(r+g+b)/3 )&0xFF;

        // update the pixel
        *pPixel = (Uint32)transparancy << 24 | 
                  (Uint32)gray<<16 | 
                  (Uint32)gray<<8 | 
                  (Uint32)gray;
    }
}

SDL黑白转换中的预期标识符和未声明的标识符错误

1 个答案: