Method: Magick::Image#export_pixels_to_str

Defined in:

ext/RMagick/rmimage.cpp

#export_pixels_to_str(x = 0, y = 0, cols = self.columns, rows = self.rows, map = "RGB", type = Magick::CharPixel) ⇒ String

Extracts the pixel data from the specified rectangle and returns it as a string.

Returns the pixel data.

Parameters:

• x (Numeric) (defaults to: 0) —

  The offset of the rectangle from the upper-left corner of the image.

• y (Numeric) (defaults to: 0) —

  The offset of the rectangle from the upper-left corner of the image.

• cols (Numeric) (defaults to: self.columns) —

  The width of the rectangle.

• rows (Numeric) (defaults to: self.rows) —

  The height of the rectangle.

• map (String) (defaults to: "RGB") —

  A string that describes which pixel channel data is desired and the order in which it should be stored. It can be any combination or order of R = red, G = green, B = blue, A = alpha, C = cyan, Y = yellow, M = magenta, K = black, I = intensity (for grayscale), or P = pad.

• type (Magick::StorageType) (defaults to: Magick::CharPixel) —

  A StorageType value that specifies the C datatype to which the pixel data will be converted.

Returns:

• (String) —

  the pixel data

# File 'ext/RMagick/rmimage.cpp', line 6776

VALUE
Image_export_pixels_to_str(int argc, VALUE *argv, VALUE self)
{
    Image *image;
    long x_off = 0L, y_off = 0L;
    unsigned long cols, rows;
    unsigned long npixels;
    size_t sz;
    MagickBooleanType okay;
    const char *map = "RGB";
    StorageType type = CharPixel;
    VALUE string;
    ExceptionInfo *exception;

    image = rm_check_destroyed(self);
    cols = image->columns;
    rows = image->rows;

    switch (argc)
    {
        case 6:
            VALUE_TO_ENUM(argv[5], type, StorageType);
        case 5:
            map   = StringValueCStr(argv[4]);
        case 4:
            rows  = NUM2ULONG(argv[3]);
        case 3:
            cols  = NUM2ULONG(argv[2]);
        case 2:
            y_off = NUM2LONG(argv[1]);
        case 1:
            x_off = NUM2LONG(argv[0]);
        case 0:
            break;
        default:
            rb_raise(rb_eArgError, "wrong number of arguments (%d for 0 to 6)", argc);
            break;
    }

    if (   x_off < 0 || (unsigned long)x_off > image->columns
           || y_off < 0 || (unsigned long)y_off > image->rows
           || cols == 0 || rows == 0)
    {
        rb_raise(rb_eArgError, "invalid extract geometry");
    }


    npixels = cols * rows * strlen(map);
    switch (type)
    {
        case CharPixel:
            sz = sizeof(unsigned char);
            break;
        case ShortPixel:
            sz = sizeof(unsigned short);
            break;
        case DoublePixel:
            sz = sizeof(double);
            break;
        case FloatPixel:
            sz = sizeof(float);
            break;
        case LongPixel:
            sz = sizeof(unsigned long);
            break;
        case QuantumPixel:
            sz = sizeof(Quantum);
            break;
        case UndefinedPixel:
        default:
            rb_raise(rb_eArgError, "undefined storage type");
            break;
    }

    // Allocate a string long enough to hold the exported pixel data.
    // Get a pointer to the buffer.
    string = rb_str_new2("");
    rb_str_resize(string, (long)(sz * npixels));

    exception = AcquireExceptionInfo();

    GVL_STRUCT_TYPE(ExportImagePixels) args = { image, x_off, y_off, cols, rows, map, type, (void *)RSTRING_PTR(string), exception };
    void *ret = CALL_FUNC_WITHOUT_GVL(GVL_FUNC(ExportImagePixels), &args);
    okay = static_cast<MagickBooleanType>(reinterpret_cast<intptr_t &>(ret));
    if (!okay)
    {
        // Let GC have the string buffer.
        rb_str_resize(string, 0);
        CHECK_EXCEPTION();

        // Should never get here...
        rm_magick_error("ExportImagePixels failed with no explanation.");
    }

    DestroyExceptionInfo(exception);

    RB_GC_GUARD(string);

    return string;
}