--- png.c.orig	2011-05-22 09:39:51.000000000 +0200
+++ png.c	2011-05-22 09:44:09.000000000 +0200
@@ -6,5 +6,137 @@
  *
  */
 
+#ifndef NO_DISPLAY_WINDOW
+
 static const char rcsid[] = "$Id: png.c,v 1.3 2002/06/10 21:25:48 chris Exp $";
 
+#include <stdlib.h>
+#include <png.h>
+#include "img.h"
+
+struct png_state {
+    png_structp png;
+    png_infop info;
+    int depth;
+    int color;
+};
+
+static void png_done(img I) {
+    struct png_state *p = I->us;
+    if (p) {
+	png_destroy_read_struct(&p->png, &p->info, 0);
+	free(p);
+    }
+}
+
+/* png_catch_error: */
+/* Catch errors signalled by libpng, clean up and go on. */
+void png_catch_error(png_structp png_ptr, png_const_charp error_msg) {
+   jmp_buf *jmpbuf_ptr;
+   
+   fprintf(stderr, "libpng error: %s (skipping image).\n", error_msg);
+   fflush(stderr);
+
+   jmpbuf_ptr=png_jmpbuf(png_ptr);
+   if (jmpbuf_ptr==NULL) {
+      fprintf(stderr, "libpng unrecoverable error, terminating.\n");
+      fflush(stderr);
+      exit(20);
+   }
+
+   longjmp(jmpbuf_ptr, 1);
+}
+         
+/* png_load_hdr:
+ * Load the header of a PNG file. */
+int png_load_hdr(img I) {
+    struct png_state *p = calloc(sizeof(struct png_state), 1);
+    if (p == 0) {
+	I->err = IE_HDRFORMAT;
+	return 0;
+    }
+    I->us = p;
+    p->png = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, png_catch_error, NULL);
+    if (p->png == 0) {
+	png_done(I);
+	I->err = IE_HDRFORMAT;
+	return 0;
+    }
+
+    if (setjmp(png_jmpbuf(p->png))) {
+       png_done(I);
+       I->err = IE_HDRFORMAT;
+       return 0;
+    }
+
+    p->info = png_create_info_struct(p->png);
+    if (p->info == 0) {
+	png_done(I);
+	I->err = IE_HDRFORMAT;
+	return 0;
+    }
+    png_init_io(p->png, I->fp);
+    png_read_info(p->png, p->info);
+    png_get_IHDR(p->png, p->info,
+		 (png_uint_32 *)&I->width, (png_uint_32 *)&I->height,
+		 &p->depth, &p->color, 0, 0, 0);
+    switch (p->color) {
+      case PNG_COLOR_TYPE_GRAY:
+      case PNG_COLOR_TYPE_GRAY_ALPHA:
+      case PNG_COLOR_TYPE_PALETTE:
+      case PNG_COLOR_TYPE_RGB:
+      case PNG_COLOR_TYPE_RGB_ALPHA:
+	return 1;
+      default:
+	png_done(I);
+	I->err = IE_IMGFORMAT;
+	return 0;
+    }
+}
+
+/* png_abort_load:
+ * Abort loading a PNG after the header is done. */
+int png_abort_load(img I) {
+    png_done(I);
+    return 1;
+}
+
+/* png_load_img:
+ * Read a PNG file into an image. */
+int png_load_img(img I) {
+    struct png_state *p = I->us;
+    img_alloc(I);
+    switch (p->depth) {
+      case 8:
+	break;
+      case 16:
+	png_set_strip_16(p->png);
+	break;
+      default:
+	png_set_packing(p->png);
+	break;
+    }
+    switch (p->color) {
+      case PNG_COLOR_TYPE_GRAY:
+      case PNG_COLOR_TYPE_GRAY_ALPHA:
+	png_set_gray_to_rgb(p->png);
+	break;
+      case PNG_COLOR_TYPE_PALETTE:
+	png_set_palette_to_rgb(p->png);
+	break;
+      case PNG_COLOR_TYPE_RGB:
+      case PNG_COLOR_TYPE_RGB_ALPHA:
+	break;
+      default:
+	png_done(I);
+	return 0;
+    }
+    if (!(p->color & PNG_COLOR_MASK_ALPHA))
+	png_set_filler(p->png, 0xFF, PNG_FILLER_AFTER);
+    png_read_update_info(p->png, p->info);
+    png_read_image(p->png, (png_bytep *)I->data);
+    png_done(I);
+    return 1;
+}
+
+#endif /* !NO_DISPLAY_WINDOW */