Filling an image with a constant value

To fill a grey-level image with a constant value use this routine:

      Gan_Image *pImage;

      /* create grey-level signed short image */
      pImage = gan_image_alloc_gl_s ( 200, 100 );

      /* fill with constant */
      gan_image_fill_const_gl_s ( pImage, 23 );

which fills each pixel with the value 23. For other formats of image you will need to build a structure of the relevant type, for instance

      Gan_Image *pImage;
      Gan_RGBPixel_uc rgbucPixel;

      /* create RGB unsigned character image */
      pImage = gan_image_alloc_rgb_uc ( 200, 100 );

      /* set up pixel */
      rgbucPixel.R = 34;
      rgbucPixel.G =  2;
      rgbucPixel.B = 65;

      /* fill with constant RGB value */
      gan_image_fill_const_rgb_uc ( pImage, &rgbucPixel );

Higher level routines are available using the Gan_Pixel structure:

      Gan_Image *pImage;
      Gan_Pixel Pixel;

      /* create RGBA single precision floating point image */
      pImage = gan_image_alloc_rgba_f ( 200, 100 );

      /* set up pixel */
      Pixel.format = GAN_RGB_COLOUR_ALPHA_IMAGE;
      Pixel.type = GAN_FLOAT;
      Pixel.data.rgba.f.R = 0.1F;
      Pixel.data.rgba.f.G = 0.2F;
      Pixel.data.rgba.f.B = 0.3F;
      Pixel.data.rgba.f.A = 0.4F;

      /* fill with constant RGBA value. The format & type of the pixel and
         image should match */
      gan_image_fill_const ( pImage, &Pixel );

If the Gan_Pixel structure has a different format/type to the image, use gan_image_convert_pixel_[qsi]() to convert it to the format & type of the image before calling gan_image_fill_const(). See Section 4.3.4 for details.

There is a special function gan_image_fill_zero() to fill an image with zero, whatever format and type it has:

      Gan_Image *pImage;

      /* create RGBA single precision floating point image */
      pImage = gan_image_alloc_rgba_f ( 200, 100 );

      /* set all image pixels to zero */
      gan_image_fill_zero ( pImage );

For boolean images (Section 4.4), ``zero'' is interpreted as false (GAN_FALSE), and for pointer images (Section 4.5) ``zero'' means NULL. To fill a single pixel with zero, use

      /* set a single pixel at position row=10, column=21 to zero */
      gan_image_set_pix_zero ( pImage, 10, 21 );

There are also routines to fill a rectangular sub-region of an image, either with a constant value or zero:

      Gan_Image *pImage;
      Gan_Pixel Pixel;

      /* create grey-level signed short image */
      pImage = gan_image_alloc_gl_s ( 200, 100 );

      /* set pixels in 30x40 (heightxwidth) pixel region starting at position
         100,30 (row,column) to constant value 125 */
      Pixel.format = GAN_GREY_LEVEL_IMAGE;
      Pixel.type = GAN_SHORT;
      Pixel.data.gl.s = 125;
      gan_image_fill_const_window ( pImage, 100, 30, 30, 40, &Pixel );

      /* reset image to RGB unsigned character */
      gan_image_set_rgb_uc ( pImage, 100, 50 );

      /* set pixels in 20x15 (heightxwidth) pixel region starting at position
         10,35 (row,column) to zero */
      gan_image_fill_zero_window ( pImage, 10, 35, 20, 15 );

Error detection: The image filling routines return a boolean value, so a return value of GAN_FALSE indicates failure, with the Gandalf error handling module being invoked.