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-rw-r--r--libnsgif.c101
-rw-r--r--libnsgif.h4
2 files changed, 68 insertions, 37 deletions
diff --git a/libnsgif.c b/libnsgif.c
index ea61217..502844f 100644
--- a/libnsgif.c
+++ b/libnsgif.c
@@ -66,9 +66,8 @@
/* TO-DO LIST
=================
- + Correct the usage of the background_action variable, which is actually
- an implementation of the "Disposal Method" flag in the Graphic Control
- Extension.
+ + Plain text and comment extensions could be implemented if there is any
+ interest in doing so.
*/
@@ -82,14 +81,20 @@
*/
#define GIF_PROCESS_COLOURS 0xaa000000
+/* Internal flag that a frame is invalid/unprocessed
+*/
+#define GIF_INVALID_FRAME -1
+
/* Maximum LZW bits available
*/
#define GIF_MAX_LZW 12
/* GIF Flags
*/
-#define GIF_DISPOSE_RESTORE_TO_BG 2
-#define GIF_DISPOSE_RESTORE_TO_PREV 3
+#define GIF_FRAME_COMBINE 1
+#define GIF_FRAME_CLEAR 2
+#define GIF_FRAME_RESTORE 3
+#define GIF_FRAME_QUIRKS_RESTORE 4
#define GIF_IMAGE_SEPARATOR 0x2c
#define GIF_INTERLACE_MASK 0x40
#define GIF_COLOUR_TABLE_MASK 0x80
@@ -188,7 +193,7 @@ gif_result gif_initialise(struct gif_animation *gif, gif_bitmap_callback_vt *bit
*/
gif->frame_count = 0;
gif->frame_count_partial = 0;
- gif->decoded_frame = -1;
+ gif->decoded_frame = GIF_INVALID_FRAME;
/* 6-byte GIF file header is:
*
@@ -224,7 +229,7 @@ gif_result gif_initialise(struct gif_animation *gif, gif_bitmap_callback_vt *bit
gif->colour_table_size = (2 << (gif_data[4] & GIF_COLOUR_TABLE_SIZE_MASK));
gif->background_colour = gif_data[5];
gif->aspect_ratio = gif_data[6];
- gif->dirty_frame = -1;
+ gif->dirty_frame = GIF_INVALID_FRAME;
gif->loop_count = 1;
gif_data += 7;
@@ -368,7 +373,7 @@ static gif_result gif_initialise_sprite(struct gif_animation *gif, unsigned int
/* Invalidate our currently decoded image
*/
- gif->decoded_frame = -1;
+ gif->decoded_frame = GIF_INVALID_FRAME;
return GIF_OK;
}
@@ -445,7 +450,7 @@ static gif_result gif_initialise_frame(struct gif_animation *gif, gif_bitmap_cal
/* Invalidate any previous decoding we have of this frame
*/
if (gif->decoded_frame == frame)
- gif->decoded_frame = -1;
+ gif->decoded_frame = GIF_INVALID_FRAME;
/* We pretend to initialise the frames, but really we just skip over all
the data contained within. This is all basically a cut down version of
@@ -508,8 +513,8 @@ static gif_result gif_initialise_frame(struct gif_animation *gif, gif_bitmap_cal
/* if we are clearing the background then we need to redraw enough to cover the previous
frame too
*/
- gif->frames[frame].redraw_required = ((gif->frames[frame].disposal_method == GIF_DISPOSE_RESTORE_TO_BG) ||
- (gif->frames[frame].disposal_method == GIF_DISPOSE_RESTORE_TO_PREV));
+ gif->frames[frame].redraw_required = ((gif->frames[frame].disposal_method == GIF_FRAME_CLEAR) ||
+ (gif->frames[frame].disposal_method == GIF_FRAME_RESTORE));
/* Boundary checking - shouldn't ever happen except with junk data
*/
@@ -616,6 +621,13 @@ static gif_result gif_initialise_frame_extensions(struct gif_animation *gif, con
gif->frames[frame].transparency_index = gif_data[5];
}
gif->frames[frame].disposal_method = ((gif_data[2] & GIF_DISPOSAL_MASK) >> 2);
+ /* I have encountered documentation and GIFs in the wild that use
+ * 0x04 to restore the previous frame, rather than the officially
+ * documented 0x03. I believe some (older?) software may even actually
+ * export this way. We handle this as a type of "quirks" mode.
+ */
+ if (gif->frames[frame].disposal_method == GIF_FRAME_QUIRKS_RESTORE)
+ gif->frames[frame].disposal_method = GIF_FRAME_RESTORE;
gif_data += (2 + gif_data[1]);
break;
@@ -630,11 +642,12 @@ static gif_result gif_initialise_frame_extensions(struct gif_animation *gif, con
case GIF_EXTENSION_APPLICATION:
if (gif_bytes < 17) return GIF_INSUFFICIENT_FRAME_DATA;
if ((gif_data[1] == 0x0b) &&
- (strncmp((const char *) gif_data + 3,
+ (strncmp((const char *) gif_data + 2,
"NETSCAPE2.0", 11) == 0) &&
(gif_data[13] == 0x03) &&
- (gif_data[14] == 0x01))
+ (gif_data[14] == 0x01)) {
gif->loop_count = gif_data[15] | (gif_data[16] << 8);
+ }
gif_data += (2 + gif_data[1]);
break;
@@ -696,6 +709,7 @@ gif_result gif_decode_frame(struct gif_animation *gif, unsigned int frame, gif_b
unsigned int return_value = 0;
unsigned int x, y, decode_y, burst_bytes;
unsigned int block_size;
+ int last_undisposed_frame = (frame - 1);
register unsigned char colour;
/* Ensure this frame is supposed to be decoded
@@ -716,14 +730,14 @@ gif_result gif_decode_frame(struct gif_animation *gif, unsigned int frame, gif_b
*/
if (!clear_image) {
if (frame == 0)
- gif->dirty_frame = -1;
+ gif->dirty_frame = GIF_INVALID_FRAME;
if (gif->decoded_frame == gif->dirty_frame) {
clear_image = true;
if (frame != 0)
gif_decode_frame(gif, gif->dirty_frame, bitmap_callbacks);
clear_image = false;
}
- gif->dirty_frame = -1;
+ gif->dirty_frame = GIF_INVALID_FRAME;
}
/* Get the start of our frame data and the end of the GIF data
@@ -737,19 +751,6 @@ gif_result gif_decode_frame(struct gif_animation *gif, unsigned int frame, gif_b
*/
if (gif_bytes < 12) return GIF_INSUFFICIENT_FRAME_DATA;
- /* Clear the previous frame totally. We can't just pretend we've got a smaller
- sprite and clear what we need as some frames have multiple images which would
- produce errors.
- */
- frame_data = (unsigned int *)bitmap_callbacks->bitmap_get_buffer(gif->frame_image);
- if (!frame_data)
- return GIF_INSUFFICIENT_MEMORY;
- if (!clear_image) {
- if ((frame == 0) || (gif->decoded_frame == -1))
- memset((char*)frame_data, 0x00, gif->width * gif->height * sizeof(int));
- gif->decoded_frame = frame;
- }
-
/* Save the buffer position
*/
save_buffer_position = gif->buffer_position;
@@ -844,6 +845,12 @@ gif_result gif_decode_frame(struct gif_animation *gif, unsigned int frame, gif_b
goto gif_decode_frame_exit;
}
+ /* Get the frame data
+ */
+ frame_data = (unsigned int *)bitmap_callbacks->bitmap_get_buffer(gif->frame_image);
+ if (!frame_data)
+ return GIF_INSUFFICIENT_MEMORY;
+
/* If we are clearing the image we just clear, if not decode
*/
if (!clear_image) {
@@ -859,11 +866,36 @@ gif_result gif_decode_frame(struct gif_animation *gif, unsigned int frame, gif_b
goto gif_decode_frame_exit;
}
- /* Set our dirty status
+ /* If the previous frame's disposal method requires we restore the background
+ * colour or this is the first frame, clear the frame data
+ */
+ if ((frame == 0) || (gif->decoded_frame == GIF_INVALID_FRAME)) {
+ memset((char*)frame_data, colour_table[gif->background_colour], gif->width * gif->height * sizeof(int));
+ } else if ((frame != 0) && (gif->frames[frame - 1].disposal_method == GIF_FRAME_CLEAR)) {
+ clear_image = true;
+ if ((return_value = gif_decode_frame(gif, (frame - 1), bitmap_callbacks)) != GIF_OK)
+ goto gif_decode_frame_exit;
+ clear_image = false;
+ /* If the previous frame's disposal method requires we restore the previous
+ * image, find the last image set to "do not dispose" and get that frame data
*/
- if ((gif->frames[frame].disposal_method == GIF_DISPOSE_RESTORE_TO_BG) ||
- (gif->frames[frame].disposal_method == GIF_DISPOSE_RESTORE_TO_PREV))
- gif->dirty_frame = frame;
+ } else if ((frame != 0) && (gif->frames[frame - 1].disposal_method == GIF_FRAME_RESTORE)) {
+ while ((last_undisposed_frame != -1) && (gif->frames[--last_undisposed_frame].disposal_method == GIF_FRAME_RESTORE));
+ /* If we don't find one, clear the frame data
+ */
+ if (last_undisposed_frame == -1) {
+ memset((char*)frame_data, colour_table[gif->background_colour], gif->width * gif->height * sizeof(int));
+ } else {
+ if ((return_value = gif_decode_frame(gif, last_undisposed_frame, bitmap_callbacks)) != GIF_OK)
+ goto gif_decode_frame_exit;
+ /* Get this frame's data
+ */
+ frame_data = (unsigned int *)bitmap_callbacks->bitmap_get_buffer(gif->frame_image);
+ if (!frame_data)
+ return GIF_INSUFFICIENT_MEMORY;
+ }
+ }
+ gif->decoded_frame = frame;
/* Initialise the LZW decoding
*/
@@ -921,11 +953,10 @@ gif_result gif_decode_frame(struct gif_animation *gif, unsigned int frame, gif_b
} else {
/* Clear our frame
*/
- if ((gif->frames[frame].disposal_method == GIF_DISPOSE_RESTORE_TO_BG) ||
- (gif->frames[frame].disposal_method == GIF_DISPOSE_RESTORE_TO_PREV)) {
+ if (gif->frames[frame].disposal_method == GIF_FRAME_CLEAR) {
for (y = 0; y < height; y++) {
frame_scanline = frame_data + offset_x + ((offset_y + y) * gif->width);
- memset(frame_scanline, 0x00, width * 4);
+ memset(frame_scanline, colour_table[gif->background_colour], width * 4);
}
}
diff --git a/libnsgif.h b/libnsgif.h
index 12cd8af..7c32d9f 100644
--- a/libnsgif.h
+++ b/libnsgif.h
@@ -48,7 +48,7 @@ typedef struct gif_frame {
bool virgin; /**< whether the frame has previously been used */
bool opaque; /**< whether the frame is totally opaque */
bool redraw_required; /**< whether a forcable screen redraw is required */
- char disposal_method; /**< how the previous frame should be disposed; affects plotting */
+ unsigned char disposal_method; /**< how the previous frame should be disposed; affects plotting */
bool transparency; /**< whether we acknoledge transparency */
unsigned char transparency_index; /**< the index designating a transparent pixel */
unsigned int redraw_x; /**< x co-ordinate of redraw rectangle */
@@ -99,7 +99,7 @@ typedef struct gif_animation {
unsigned int *local_colour_table; /**< local colour table */
int dirty_frame; /**< the current dirty frame, or -1 for none */
void *frame_image; /**< currently decoded image; stored as bitmap from bitmap_create callback */
- gif_result current_error; /**< current error type, or 0 for none*/
+ gif_result current_error; /**< current error type, or 0 for none*/
} gif_animation;
gif_result gif_initialise(struct gif_animation *gif, gif_bitmap_callback_vt *bitmap_callbacks);
generated by cgit v1.2.3 (git 2.39.1) at 2024-04-16 14:06:50 +0000