Display of a gray Image on 8 bit screen

[Christian Orsatti <orsatti istar fr>]

HI,

I am trying for 2 days now to display a gray level image
on an 8 bits screen with all its gray levels (ie 256)

I try several methods but none work and all get me at the
same point. A display with only 5 gray levels.
The only way to have something correct is to use dithering
but I don't want that. I need to see the pixel with it real value.

How can I do that ???
Here is the simplest code I came to but it still not working
properly and giving me (when I click on the window) only
5 gray levels.

Any help is welcome !!!!!!!

#include <gdk/gdk.h>
#include <gdk/gdkrgb.h>
#include <gtk/gtk.h>
#include <malloc.h>
#include <iostream.h>
#include <string.h>

#define LARGEUR (256)
#define HAUTEUR (256)

guchar *buf = (guchar*)NULL;
GdkWindow *Fenetre = (GdkWindow*)NULL;
void TraitementButton(GdkEventButton* ev);

int main(int argc, char *argv[)
{
  GdkWindowAttr attr;

  gdk_init(&argc, &argv);
  gdk_rgb_init();


  // Get gray scale Visual
  GdkVisual *gs = gdk_visual_get_best_with_both(8,
GDK_VISUAL_GRAYSCALE);
  if (gs == NULL) {
    cerr << "Error visual not found\n";
    return 1;
  }
  // Get a new colormap
  GdkColormap *cm = gdk_colormap_new(gs, TRUE);
  if (cm == NULL) {
    cerr << "Error colormap not created\n";
    return 1;
  }
  // Set colors of the colormap
  GdkColor *colors = (GdkColor*)malloc(256 * sizeof(GdkColor));
  for (int i=0; i<256; i++) {
    colors[i].red = i;
    colors[i].green = colors[i].blue = i;
    if (!gdk_color_alloc(cm, &colors[i])) {
      cerr << "couleur " << i << " failed\n";
    }
    else {
      cerr << i << " -> " << colors[i].pixel << endl;
    }
  }

  // Window creation
  attr.event_mask = GDK_BUTTON_PRESS_MASK;
  attr.width = LARGEUR;
  attr.height = HAUTEUR;
  attr.wclass = GDK_INPUT_OUTPUT;
  attr.window_type = GDK_WINDOW_TOPLEVEL;
  attr.visual = gs;
  attr.colormap = cm;
  Fenetre = gdk_window_new(NULL, &attr, 0);

  // Buffer
  buf = (guchar*)malloc(256*256*sizeof(guchar));
  for(int i = 0; i < 256; i++) memset(&(buf[256*i]), i, 256);

  // Display window
  gdk_window_show(Fenetre);

  // Event Loop
  while(1) {
    if (gdk_events_pending()) {
      GdkEvent *ev = gdk_event_get();
      if (ev) {
 switch (ev->type) {
 case GDK_BUTTON_PRESS:
   TraitementButton((GdkEventButton*)ev);
 default:
   cerr << ev->type << endl;
 }
 gdk_event_free(ev);
      }
    }
  }

}

void TraitementButton(GdkEventButton* ev)
{
  cerr << "Button pressed\n";
  // Draw imagw
  gdk_draw_gray_image(Fenetre,
        gdk_gc_new(Fenetre),
        0,0, LARGEUR, HAUTEUR,
        GDK_RGB_DITHER_NONE,
        buf, 256);
}