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class Fl_Image


Class Hierarchy

Include Files

    #include <FL/Fl_Image.H>
    

Description

Fl_Image is the base class used for caching and drawing all kinds of images in FLTK. This class keeps track of common image data such as the pixels, colormap, width, height, and depth. Virtual methods are used to provide type-specific image handling.

Since the Fl_Image class does not support image drawing by itself, calling the draw() method results in a box with an X in it being drawn instead.

Methods

Fl_Image(int W, int H, int D);

The constructor creates an empty image with the specified width, height, and depth. The width and height are in pixels. The depth is 0 for bitmaps, 1 for pixmap (colormap) images, and 1 to 4 for color images.

virtual ~Fl_Image();

The destructor is a virtual method that frees all memory used by the image.

virtual void color_average(Fl_Color c, float i);

The color_average() method averages the colors in the image with the FLTK color value c. The i argument specifies the amount of the original image to combine with the color, so a value of 1.0 results in no color blend, and a value of 0.0 results in a constant image of the specified color. The original image data is not altered by this method.

virtual Fl_Image *copy(int W, int H);
copy();

The copy() method creates a copy of the specified image. If the width and height are provided, the image is resized to the specified size. The image should be deleted (or in the case of Fl_Shared_Image, released) when you are done with it.

int count();

The count() method returns the number of data values associated with the image. The value will be 0 for images with no associated data, 1 for bitmap and color images, and greater than 2 for pixmap images.

int d();
protected void d(int D);

The first form of the d() method returns the current image depth. The return value will be 0 for bitmaps, 1 for pixmaps, and 1 to 4 for color images.

The second form is a protected method that sets the current image depth.

const char * const *data();
protected void data(const char * const *data, int count);

The first form of the data() method returns a pointer to the current image data array. Use the count() method to find the size of the data array.

The second form is a protected method that sets the current array pointer and count of pointers in the array.

virtual void desaturate()

The desaturate() method converts an image to grayscale. If the image contains an alpha channel (depth = 4), the alpha channel is preserved. This method does not alter the original image data.

void draw(int X, int Y);
virtual void draw(int X, int Y, int W, int H, int cx, int cy);

The draw() methods draw the image. The first form specifies the upper-lefthand corner of the image. The second form specifies a bounding box for the image, with the origin (upper-lefthand corner) of the image offset by the cx and cy arguments.

protected void draw_empty(int X, int Y);

The protected method draw_empty() draws a box with an X in it. It can be used to draw any image that lacks image data.

int h();
protected void h(int H);

The first form of the h() method returns the current image height in pixels.

The second form is a protected method that sets the current image height.

void inactive();

The inactive() method calls color_average(FL_BACKGROUND_COLOR, 0.33f) to produce an image that appears grayed out. This method does not alter the original image data.

virtual void label(Fl_Widget *w); virtual void label(Fl_Menu_Item *m);

The label() methods are an obsolete way to set the image attribute of a widget or menu item. Use the image() or deimage() methods of the Fl_Widget and Fl_Menu_Item classes instead.

int ld();
protected void ld(int LD);

The first form of the ld() method returns the current line data size in bytes. Line data is extra data that is included after each line of color image data and is normally not present.

The second form is a protected method that sets the current line data size in bytes.

void uncache();

If the image has been cached for display, delete the cache data. This allows you to change the data used for the image and then redraw it without recreating an image object.

int w();
protected void w(int W);

The first form of the w() method returns the current image width in pixels.

The second form is a protected method that sets the current image width.


User Comments [ Add Comment ]

From Anonymous, 21:11 Dec 10, 2008 (score=3)

The data() and count() explanations leave a lot to be desired. How is the "image data array" formatted and how do we get the pixels out? With RGB images it's easy to figure out after a quick look at Erco's cheat page, but what about indexed (paletted) images?

It turns out indexed images are stored by fltk in a format very similar to XPM. The members of the data array are as follows:

[0]       (char *)          : null-terminated string containing image information.
[1]       (unsigned char *) : palette data (4 * palette length: index, r, g, b for each entry)
[2...H+2] (char *)          : null-terminated string of characters representing palette indices

The exception to this rule is XPM images, which are stored with the normal (not compressed) XPM palette, so data[1] is an array of null-terminated strings.

In arrays 2 through H(eight)+2, a space always represents transparency.

This code sample should help explain how to get pixel values out of indexed images. Uncomment some of the printf statements to get a better idea of what's going on.

// Convert fltk shared image to PNG.

#ifndef _IMAGE_H
#define _IMAGE_H 1

#include "map"
#include "string"

#include <FL/Fl_Shared_Image.H>
#include "png.hpp"


class ImageHandler
{
public:
  
  // save image as a png
  static bool save(Fl_Shared_Image *image, const char *filename) 
  {
    if (image->count() > 1) 
      return save_indexed(image, filename);
    else 
      return save_inline(image, filename);
  }

protected:
    
  // save indexed images (gif... no xpm support yet)
  static bool save_indexed(Fl_Shared_Image *image, const char *filename) // indexed images
  {
    png::image< png::rgba_pixel > png(image->w(), image->h());

    const char * const *data = image->data();
    
    // printf("Converting indexed image: %s\n",data[0]);
    
    //  fltk compressed palette length is stored as negative number - make sure it exists
    std::string id(data[0]);  // string containing image data
    if (id.find_first_of('-') == std::string::npos)
    {
      fprintf(stderr,"XPM to PNG not currently supported.\n");
      return false;
    }
    
    // extract palette size from image data string
    int palsize = atoi(id.substr( id.find_first_of('-') +1, id.size() - id.find_last_of(' ') ).c_str());
    
    // printf("Palette size: %i\n",palsize);
    // for (int i = 2; i<image->count(); i++) printf("%s\n", data[i]);
    
    // map fltk palette index characters to their position in the palette data array
    uchar *pd = (uchar *)data[1]; // palette data array
    std::map<uchar, int> palette; 
    for (uchar c=0; c<palsize*4; c+=4) 
    {
      palette[pd[c]] = c;
      //printf("%c: %02x%02x%02x \n", pd[c],pd[c+1],pd[c+2],pd[c+3]);
    }
    
    for ( int y=0; y<image->h(); y++ )  // Y loop
    {                              
      for ( int x=0; x<image->w(); x++ ) // X loop
      {                           
        const char *buf = image->data()[y+2];

        char i = *(buf+x);  // character we are on representing a palette index
        
        char r,g,b,a;
        r=g=b=0;  // color defaults to black
        a=255;  // alpha defaults to fully visible
        
        // set alpha to 0 for transparent pixels
        if (i == ' ')
        {
          a = 0;
          continue;
        }
        
        // set the pixel in the pngpp image
        r = pd[palette[i]+1];
        g = pd[palette[i]+2];
        b = pd[palette[i]+3];
        png.set_pixel(x,y,png::rgba_pixel(r,g,b,a));
        
      } // end Y loop
    } // end X loop
  
    png.write(filename);  // write the pngpp image to disk
    
    // printf("depth: %i  /  width: %i  /  height: %i / count: %i \n", image->d(), image->w(), image->h(), image->count());
    
    return true;
  } // end save_indexed
  
  // save non-indexed images (bmp, jpg, pnm) (see Erco's cheat page)
  static bool save_inline(Fl_Shared_Image *image, const char *filename)  // non-indexed images
  {
    // printf("Converting color image\n");
    png::image< png::rgba_pixel > png(image->w(), image->h());
    const char *buf = image->data()[0];

    
    for ( int y=0; y<image->h(); y++ )  // Y loop
    {                              
      for ( int x=0; x<image->w(); x++ ) // X loop
      {                           
        long index = (y * image->w() * image->d()) + (x * image->d()); // X/Y -> buf index
        
        char r,g,b,a;
        r=g=b=0;
        a=0xFF;
        
        switch ( image->d() ) // check image depth
        {          
          case 4: // 24bit + alpha
          {                                    
            a = *(buf+index+3);
          }
          case 3:  // 24bit                                    
          {
            r = *(buf+index+0);
            g = *(buf+index+1);
            b = *(buf+index+2);
            break;
          case 2:  // 8bit + alpha
          {                                   
            a = *(buf+index+1);
          }
          case 1:  // 8bit
          {                                    
            r = g = b = *(buf+index);
            break;
          }
          }
          // fl reports depth 0 for xbm... add support here
          default:                                     // ??
          {
            fprintf(stderr, "Not supported: %d channels\n", image->d());
            return false;
          }
        }
        
        png.set_pixel(x,y,png::rgba_pixel(r,g,b,a));
      } // end Y loop
    } // end X loop
  
    png.write(filename);
    return true;
  } // end save_inline

    
};  // end class

#endif


Reply ]

From gebhart, 14:40 Jan 04, 2006 (score=3)

Is there any way to get the coordinates of a mouse-click when the user clicks on an image, without writing your own class?

I am developing a program with a combination of FLTK and C (no classes) and have an Fl_RGB_Image associated with a Fl_Box in my program. I would like to know the coordinates of a mouse-click when the user clicks on the image. Unfortunately, I am not developing my own classes, the callback of the Fl_Box is not invoked when I click on the image, and Fl_RGB_Image does not have a callback function tied to it.

Any ideas?
Reply ]

 
 

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