gtk_tut-13.html

gtk 开发手册和参考文档。 包括gtk glib gdk等

implementation of reducing the image. (Keep in mind that I've had only basic
C!)

(UNTESTED CODE ALERT!!!)

typedef struct {
  gint      width;
  gint      height;
  gint      bbp;
  guchar    *rgb;
  guchar    *mask;
} ReducedImage;

enum {
  SELECTION_ONLY,
  SELCTION_IN_CONTEXT,
  ENTIRE_IMAGE
};

ReducedImage *Reduce_The_Image(GDrawable *drawable,
                               GDrawable *mask,
                               gint LongerSize,
                               gint Selection)
{
  /* This function reduced the image down to the the selected preview size */
  /* The preview size is determine by LongerSize, i.e. the greater of the  */
  /* two dimentions. Works for RGB images only!                            */
  gint RH, RW;          /* Reduced height and reduced width                */
  gint width, height;   /* Width and Height of the area being reduced      */
  gint bytes=drawable->bpp;
  ReducedImage *temp=(ReducedImage *)malloc(sizeof(ReducedImage));

  guchar *tempRGB, *src_row, *tempmask, *src_mask_row,R,G,B;
  gint i, j, whichcol, whichrow, x1, x2, y1, y2;
  GPixelRgn srcPR, srcMask;
  gint NoSelectionMade=TRUE; /* Assume that we're dealing with the entire  */
                             /* image.                                     */

  gimp_drawable_mask_bounds (drawable->id, &x1, &y1, &x2, &y2);
  width  = x2-x1;
  height = y2-y1;
  /* If there's a SELECTION, we got its bounds!)

  if (width != drawable->width && height != drawable->height)
    NoSelectionMade=FALSE;
  /* Become aware of whether the user has made an active selection   */
  /* This will become important later, when creating a reduced mask. */

  /* If we want to preview the entire image, overrule the above!  */
  /* Of course, if no selection has been made, this does nothing! */
  if (Selection==ENTIRE_IMAGE) {
    x1=0;
    x2=drawable->width;
    y1=0;
    y2=drawable->height;
  }

  /* If we want to preview a selection with some surronding area we */
  /* have to expand it a little bit. Consider it a bit of a riddle. */
  if (Selection==SELECTION_IN_CONTEXT) {
    x1=MAX(0,                x1-width/2.0);
    x2=MIN(drawable->width,  x2+width/2.0);
    y1=MAX(0,                y1-height/2.0);
    y2=MIN(drawable->height, y2+height/2.0);
  }

  /* How we can determine the width and the height of the area being */
  /* reduced.                                                        */
  width  = x2-x1;
  height = y2-y1;

  /* The lines below determine which dimension is to be the longer   */
  /* side. The idea borrowed from the supernova plug-in. I suspect I */
  /* could've thought of it myself, but the truth must be told.      */
  /* Plagiarism stinks!                                               */
  if (width>height) {
    RW=LongerSize;
    RH=(float) height * (float) LongerSize/ (float) width;
  }
  else {
    RH=LongerSize;
    RW=(float)width * (float) LongerSize/ (float) height;
  }

  /* The intire image is stretched into a string! */
  tempRGB   = (guchar *) malloc(RW*RH*bytes);
  tempmask  = (guchar *) malloc(RW*RH);

  gimp_pixel_rgn_init (&srcPR, drawable, x1, y1, width, height, FALSE, FALSE);
  gimp_pixel_rgn_init (&srcMask, mask, x1, y1, width, height, FALSE, FALSE);

  /* Grab enough to save a row of image and a row of mask. */
  src_row       = (guchar *) malloc (width*bytes);
  src_mask_row  = (guchar *) malloc (width);

  for (i=0; i < RH; i++) {
    whichrow=(float)i*(float)height/(float)RH;
    gimp_pixel_rgn_get_row (&srcPR, src_row, x1, y1+whichrow, width);
    gimp_pixel_rgn_get_row (&srcMask, src_mask_row, x1, y1+whichrow, width);

    for (j=0; j < RW; j++) {
      whichcol=(float)j*(float)width/(float)RW;

      /* No selection made = each point is completely selected! */
      if (NoSelectionMade)
        tempmask[i*RW+j]=255;
      else
        tempmask[i*RW+j]=src_mask_row[whichcol];

      /* Add the row to the one long string which now contains the image! */
      tempRGB[i*RW*bytes+j*bytes+0]=src_row[whichcol*bytes+0];
      tempRGB[i*RW*bytes+j*bytes+1]=src_row[whichcol*bytes+1];
      tempRGB[i*RW*bytes+j*bytes+2]=src_row[whichcol*bytes+2];

      /* Hold on to the alpha as well */
      if (bytes==4)
        tempRGB[i*RW*bytes+j*bytes+3]=src_row[whichcol*bytes+3];
    }
  }
  temp->bpp=bytes;
  temp->width=RW;
  temp->height=RH;
  temp->rgb=tempRGB;
  temp->mask=tempmask;
  return temp;
}

The following is a preview function which used the same ReducedImage type!
Note that it uses fakes transparancy (if one is present by means of
fake_transparancy which is defined as follows:

gint fake_transparency(gint i, gint j)
{
  if ( ((i%20)- 10) * ((j%20)- 10)>0   )
    return 64;
  else
    return 196;
}

Now here's the preview function:

void
my_preview_render_function(GtkWidget     *preview,
                           gint          changewhat,
                           gint          changewhich)
{
  gint Inten, bytes=drawable->bpp;
  gint i, j, k;
  float partial;
  gint RW=reduced->width;
  gint RH=reduced->height;
  guchar *row=malloc(bytes*RW);;


  for (i=0; i < RH; i++) {
    for (j=0; j < RW; j++) {

      row[j*3+0] = reduced->rgb[i*RW*bytes + j*bytes + 0];
      row[j*3+1] = reduced->rgb[i*RW*bytes + j*bytes + 1];
      row[j*3+2] = reduced->rgb[i*RW*bytes + j*bytes + 2];

      if (bytes==4)
        for (k=0; k<3; k++) {
          float transp=reduced->rgb[i*RW*bytes+j*bytes+3]/255.0;
          row[3*j+k]=transp*a[3*j+k]+(1-transp)*fake_transparency(i,j);
        }
    }
    gtk_preview_draw_row( GTK_PREVIEW(preview),row,0,i,RW);
  }

  free(a);
  gtk_widget_draw(preview,NULL);
  gdk_flush();
}

Applicable Routines

guint           gtk_preview_get_type           (void);
/* No idea */
void            gtk_preview_uninit             (void);
/* No idea */
GtkWidget*      gtk_preview_new                (GtkPreviewType   type);
/* Described above */
void            gtk_preview_size               (GtkPreview      *preview,
                                                gint             width,
                                                gint             height);
/* Allows you to resize an existing preview.    */
/* Apparantly there's a bug in GTK which makes  */
/* this process messy. A way to clean up a mess */
/* is to manually resize the window containing  */
/* the preview after resizing the preview.      */

void            gtk_preview_put                (GtkPreview      *preview,
                                                GdkWindow       *window,
                                                GdkGC           *gc,
                                                gint             srcx,
                                                gint             srcy,
                                                gint             destx,
                                                gint             desty,
                                                gint             width,
                                                gint             height);
/* No idea */

void            gtk_preview_put_row            (GtkPreview      *preview,
                                                guchar          *src,
                                                guchar          *dest,
                                                gint             x,
                                                gint             y,
                                                gint             w);
/* No idea */

void            gtk_preview_draw_row           (GtkPreview      *preview,
                                                guchar          *data,
                                                gint             x,
                                                gint             y,
                                                gint             w);
/* Described in the text */

void            gtk_preview_set_expand         (GtkPreview      *preview,
                                                gint             expand);
/* No idea */

/* No clue for any of the below but    */
/* should be standard for most widgets */
void            gtk_preview_set_gamma          (double           gamma);
void            gtk_preview_set_color_cube     (guint            nred_shades,
                                                guint            ngreen_shades,
                                                guint            nblue_shades,
                                                guint            ngray_shades);
void            gtk_preview_set_install_cmap   (gint             install_cmap);
void            gtk_preview_set_reserved       (gint             nreserved);
GdkVisual*      gtk_preview_get_visual         (void);
GdkColormap*    gtk_preview_get_cmap           (void);
GtkPreviewInfo* gtk_preview_get_info           (void);

That's all, folks!
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<H2><A NAME="ss13.7">13.7 Curves</A>
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