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Attempt to rationalize handling of logical screen.
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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.
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@kohler
kohler committed Mar 2, 2024
1 parent b7cc4c1 commit 33015b1
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Showing 4 changed files with 76 additions and 71 deletions.
15 changes: 3 additions & 12 deletions src/giffunc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
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4 changes: 2 additions & 2 deletions src/opttemplate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
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83 changes: 38 additions & 45 deletions src/support.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand All @@ -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
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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);
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45 changes: 33 additions & 12 deletions src/xform.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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);
}

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