Attempt to rationalize handling of logical screen.

Rather than override input GIF logical streams with the largest
implied screen of all images, interpret the logical screen the same
way Chrome does: the max of the input screen and the *first* image.

This fixes #199. It will change behavior for some GIFs but I hope
not too badly. It requires some care, since it means that (unlike
previously) some images in a GIF considered by Gifsicle will have
frames partially or completely out of range.

Author: kohler

src/giffunc.c

@@ -300,26 +300,17 @@ void
 Gif_CalculateScreenSize(Gif_Stream *gfs, int force)
 {
   int i;
-  int screen_width = 0;
-  int screen_height = 0;
+  int screen_width = force ? 0 : gfs->screen_width;
+  int screen_height = force ? 0 : gfs->screen_height;
 
-  for (i = 0; i < gfs->nimages; i++) {
+  for (i = 0; i < gfs->nimages && (force || i == 0); ++i) {
     Gif_Image *gfi = gfs->images[i];
-    /* 17.Dec.1999 - I find this old behavior annoying. */
-    /* if (gfi->left != 0 || gfi->top != 0) continue; */
     if (screen_width < gfi->left + gfi->width)
       screen_width = gfi->left + gfi->width;
     if (screen_height < gfi->top + gfi->height)
       screen_height = gfi->top + gfi->height;
   }
 
-  /* Only use the default 640x480 screen size if we are being forced to create
-     a new screen size or there's no screen size currently. */
-  if (screen_width == 0 && (gfs->screen_width == 0 || force))
-    screen_width = 640;
-  if (screen_height == 0 && (gfs->screen_height == 0 || force))
-    screen_height = 480;
-
   if (gfs->screen_width < screen_width || force)
     gfs->screen_width = screen_width;
   if (gfs->screen_height < screen_height || force)

src/opttemplate.c

@@ -250,8 +250,8 @@ X(find_difference_bounds)(Gif_OptData *bounds, Gif_Image *gfi, Gif_Image *last)
 
   /* 19.Aug.1999 - handle case when there's no difference between frames */
   if (tp > bt) {
-    tp = bt = gfi->top;
-    lf = rt = gfi->left;
+    tp = bt = constrain(0, gfi->top, screen_height - 1);
+    lf = rt = constrain(0, gfi->left, screen_width - 1);
   }
 
   bounds->left = lf;

src/support.c

@@ -1253,21 +1253,8 @@ fix_total_crop(Gif_Stream *dest, Gif_Image *srci, int merger_index)
 
 
 static void
-handle_screen(Gif_Stream *dest, uint16_t width, uint16_t height)
+handle_flip_and_rotate(Gif_Image* desti, Gt_Frame* fr)
 {
-    /* Set the screen width & height, if the current input width and height are
-       larger */
-    if (dest->screen_width < width)
-        dest->screen_width = width;
-    if (dest->screen_height < height)
-        dest->screen_height = height;
-}
-
-static void
-handle_flip_and_screen(Gif_Stream* dest, Gif_Image* desti, Gt_Frame* fr)
-{
-    Gif_Stream* gfs = fr->stream;
-
     desti->left += fr->left_offset;
     desti->top += fr->top_offset;
 
@@ -1286,12 +1273,6 @@ handle_flip_and_screen(Gif_Stream* dest, Gif_Image* desti, Gt_Frame* fr)
 
     desti->left -= fr->left_offset;
     desti->top -= fr->top_offset;
-
-    /* handle screen size, which might have height & width exchanged */
-    if (fr->rotation == 1 || fr->rotation == 3)
-        handle_screen(dest, gfs->screen_height, gfs->screen_width);
-    else
-        handle_screen(dest, gfs->screen_width, gfs->screen_height);
 }
 
 static void
@@ -1611,11 +1592,10 @@ merge_frame_interval(Gt_Frameset *fset, int f1, int f2,
 
     srci->transparent = old_transp; /* restore real transparent value */
 
-    /* Flipping and rotating, and also setting the screen size */
-    if (fr->flip_horizontal || fr->flip_vertical || fr->rotation)
-        handle_flip_and_screen(dest, desti, fr);
-    else
-        handle_screen(dest, fr->stream->screen_width, fr->stream->screen_height);
+    /* Flipping and rotating */
+    if (fr->flip_horizontal || fr->flip_vertical || fr->rotation) {
+      handle_flip_and_rotate(desti, fr);
+    }
 
     /* Names and comments */
     if (fr->name || fr->no_name) {
@@ -1663,6 +1643,37 @@ merge_frame_interval(Gt_Frameset *fset, int f1, int f2,
       desti->disposal = fr->disposal;
     }
 
+    /* logical screen */
+    if (output_data->screen_mode <= 0) {
+      int w, h;
+      if (output_data->screen_mode < 0
+          || fr->crop
+          || ((fr->left >= 0 || fr->top >= 0) && !fr->position_is_offset)) {
+        w = desti->left + desti->width;
+        h = desti->top + desti->height;
+      } else {
+        if (fr->rotation == 1 || fr->rotation == 3) {
+          w = fr->stream->screen_height;
+          h = fr->stream->screen_width;
+        } else {
+          w = fr->stream->screen_width;
+          h = fr->stream->screen_height;
+        }
+        if (fr->left >= 0) {
+          w += fr->left;
+        }
+        if (fr->top >= 0) {
+          h += fr->top;
+        }
+      }
+      if (w > dest->screen_width) {
+        dest->screen_width = w;
+      }
+      if (h > dest->screen_height) {
+        dest->screen_height = h;
+      }
+    }
+
     /* compress immediately if possible to save on memory */
     if (desti->img) {
       if (compress_immediately > 0) {
@@ -1710,28 +1721,10 @@ merge_frame_interval(Gt_Frameset *fset, int f1, int f2,
   }
   /** END MERGE LOOP **/
 
-  /* Cropping the whole output? Reset logical screen */
-  if (merger[0]->crop && merger[0]->crop == merger[nmerger - 1]->crop) {
-    /* 13.May.2008: Set the logical screen to the cropped dimensions */
-    /* 18.May.2008: Unless --crop-transparency is on */
-    Gt_Crop* crop = merger[0]->crop;
-    if (crop->transparent_edges)
-        dest->screen_width = dest->screen_height = 0;
-    else if (merger[0]->rotation == 1 || merger[0]->rotation == 3) {
-        dest->screen_width = (crop->h > 0 ? crop->h : 0);
-        dest->screen_height = (crop->w > 0 ? crop->w : 0);
-    } else {
-        dest->screen_width = (crop->w > 0 ? crop->w : 0);
-        dest->screen_height = (crop->h > 0 ? crop->h : 0);
-    }
-  }
-
-  /* Set the logical screen from the user's preferences */
-  if (output_data->screen_width >= 0)
+  if (output_data->screen_mode == 1) {
     dest->screen_width = output_data->screen_width;
-  if (output_data->screen_height >= 0)
     dest->screen_height = output_data->screen_height;
-  Gif_CalculateScreenSize(dest, 0);
+  }
 
   /* Find the background color in the colormap, or add it if we can */
   set_background(dest, output_data);

src/xform.c

@@ -325,6 +325,7 @@ rotate_image(Gif_Image* gfi, Gt_Frame* fr, int rotation)
   int x, y;
   int width = gfi->width;
   int height = gfi->height;
+  int ntop, nleft, nbottom, nright;
   uint8_t **img = gfi->img;
   uint8_t *new_data = Gif_NewArray(uint8_t, (unsigned) width * (unsigned) height);
   uint8_t *trav = new_data;
@@ -336,32 +337,52 @@ rotate_image(Gif_Image* gfi, Gt_Frame* fr, int rotation)
     for (x = 0; x < width; x++)
       for (y = height - 1; y >= 0; y--)
         *trav++ = img[y][x];
-    x = gfi->left;
-    gfi->left = fr->stream->screen_height - (gfi->top + height);
-    gfi->top = x;
+  } else {
+    for (x = width - 1; x >= 0; x--)
+      for (y = 0; y < height; y++)
+        *trav++ = img[y][x];
+  }
+
+  if (rotation == 1) {
+    ntop = gfi->left;
+    nleft = fr->stream->screen_height - (gfi->top + height);
     if (fr->crop) {
         x = fr->left_offset;
         fr->left_offset = fr->stream->screen_height - (fr->top_offset + fr->crop->h);
         fr->top_offset = x;
     }
-
   } else {
-    for (x = width - 1; x >= 0; x--)
-      for (y = 0; y < height; y++)
-        *trav++ = img[y][x];
-    y = gfi->top;
-    gfi->top = fr->stream->screen_width - (gfi->left + width);
-    gfi->left = y;
+    ntop = fr->stream->screen_width - (gfi->left + width);
+    nleft = gfi->top;
     if (fr->crop) {
         y = fr->top_offset;
         fr->top_offset = fr->stream->screen_width - (fr->left_offset + fr->crop->w);
         fr->left_offset = y;
     }
   }
+  nbottom = ntop + width;
+  nright = nleft + height;
+
+  if (nbottom <= 0 || nright <= 0) {
+    ntop = nleft = nbottom = nright = 0;
+  } else if (ntop < 0 || nleft < 0) {
+    int nwidth = nright - (nleft < 0 ? 0 : nleft);
+    uint8_t *xdata;
+    xdata = Gif_NewArray(uint8_t, (unsigned) (nright - nleft) * (unsigned) (nbottom - ntop));
+    for (y = ntop < 0 ? -ntop : 0; y < width; ++y) {
+        memcpy(xdata + y * nwidth, new_data + y * height + (nleft < 0 ? -nleft : 0), nwidth);
+    }
+    Gif_DeleteArray(new_data);
+    new_data = xdata;
+    ntop = ntop < 0 ? 0 : ntop;
+    nleft = nleft < 0 ? 0 : nleft;
+  }
 
   Gif_ReleaseUncompressedImage(gfi);
-  gfi->width = height;
-  gfi->height = width;
+  gfi->width = nright - nleft;
+  gfi->height = nbottom - ntop;
+  gfi->left = nleft;
+  gfi->top = ntop;
   Gif_SetUncompressedImage(gfi, new_data, Gif_Free, 0);
 }