Method: Magick::Image#get_pixels

Defined in:
ext/RMagick/rmimage.cpp

#get_pixels(x_arg, y_arg, cols_arg, rows_arg) ⇒ Array<Magick::Pixel>

Gets the pixels from the specified rectangle within the image.

Parameters:

  • x_arg (Numeric) —

    x position of start of region

  • y_arg (Numeric) —

    y position of start of region

  • cols_arg (Numeric) —

    width of region

  • rows_arg (Numeric) —

    height of region

Returns:

  • (Array<Magick::Pixel>) —

    An array of Magick::Pixel objects corresponding to the pixels in the rectangle defined by the geometry parameters.

See Also:



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# File 'ext/RMagick/rmimage.cpp', line 7819

VALUE
Image_get_pixels(VALUE self, VALUE x_arg, VALUE y_arg, VALUE cols_arg, VALUE rows_arg)
{
    Image *image;
    ExceptionInfo *exception;
    long x, y;
    unsigned long columns, rows;
    long size, n;
    VALUE pixel_ary;
#if defined(IMAGEMAGICK_7)
    const Quantum *pixels;
#else
    const PixelPacket *pixels;
    const IndexPacket *indexes;
#endif

    image = rm_check_destroyed(self);
    x       = NUM2LONG(x_arg);
    y       = NUM2LONG(y_arg);
    columns = NUM2ULONG(cols_arg);
    rows    = NUM2ULONG(rows_arg);

    if ((x+columns) > image->columns || (y+rows) > image->rows)
    {
        rb_raise(rb_eRangeError, "geometry (%lux%lu%+ld%+ld) exceeds image bounds",
                 columns, rows, x, y);
    }

    // Cast AcquireImagePixels to get rid of the const qualifier. We're not going
    // to change the pixels but I don't want to make "pixels" const.
    exception = AcquireExceptionInfo();
    GVL_STRUCT_TYPE(GetVirtualPixels) args = { image, x, y, columns, rows, exception };
    void *ret = CALL_FUNC_WITHOUT_GVL(GVL_FUNC(GetVirtualPixels), &args);
    pixels = reinterpret_cast<decltype(pixels)>(ret);
    CHECK_EXCEPTION();

    DestroyExceptionInfo(exception);

    // If the function failed, return a 0-length array.
    if (!pixels)
    {
        return rb_ary_new();
    }

    // Allocate an array big enough to contain the PixelPackets.
    size = (long)(columns * rows);
    pixel_ary = rb_ary_new2(size);

#if defined(IMAGEMAGICK_6)
    indexes = GetVirtualIndexQueue(image);
#endif

    // Convert the PixelPackets to Magick::Pixel objects
    for (n = 0; n < size; n++)
    {
#if defined(IMAGEMAGICK_7)
        PixelPacket color;
        memset(&color, 0, sizeof(color));
        color.red   = GetPixelRed(image, pixels);
        color.green = GetPixelGreen(image, pixels);
        color.blue  = GetPixelBlue(image, pixels);
        color.alpha = GetPixelAlpha(image, pixels);
        color.black = GetPixelBlack(image, pixels);
        rb_ary_store(pixel_ary, n, Pixel_from_PixelPacket(&color));

        pixels += GetPixelChannels(image);
#else
        MagickPixel mpp;
        mpp.red = GetPixelRed(pixels);
        mpp.green = GetPixelGreen(pixels);
        mpp.blue = GetPixelBlue(pixels);
        mpp.opacity = GetPixelOpacity(pixels);
        if (indexes)
        {
            mpp.index = GetPixelIndex(indexes + n);
        }
        rb_ary_store(pixel_ary, n, Pixel_from_MagickPixel(&mpp));
        pixels++;
#endif
    }

    return pixel_ary;
}