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libvips/libvips/foreign/libnsgif/libnsgif.c

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/*
* Copyright 2004 Richard Wilson <richard.wilson@netsurf-browser.org>
* Copyright 2008 Sean Fox <dyntryx@gmail.com>
*
* This file is part of NetSurf's libnsgif, http://www.netsurf-browser.org/
* Licenced under the MIT License,
* http://www.opensource.org/licenses/mit-license.php
*/
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include "libnsgif.h"
#include "utils/log.h"
#include "lzw.h"
/**
*
* \file
* \brief GIF image decoder
*
* The GIF format is thoroughly documented; a full description can be found at
* http://www.w3.org/Graphics/GIF/spec-gif89a.txt
*
* \todo Plain text and comment extensions should be implemented.
*/
/** Maximum colour table size */
#define GIF_MAX_COLOURS 256
/** Internal flag that the colour table needs to be processed */
#define GIF_PROCESS_COLOURS 0xaa000000
/** Internal flag that a frame is invalid/unprocessed */
#define GIF_INVALID_FRAME -1
/** Transparent colour */
#define GIF_TRANSPARENT_COLOUR 0x00
/* GIF Flags */
#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
#define GIF_COLOUR_TABLE_SIZE_MASK 0x07
#define GIF_EXTENSION_INTRODUCER 0x21
#define GIF_EXTENSION_GRAPHIC_CONTROL 0xf9
#define GIF_DISPOSAL_MASK 0x1c
#define GIF_TRANSPARENCY_MASK 0x01
#define GIF_EXTENSION_COMMENT 0xfe
#define GIF_EXTENSION_PLAIN_TEXT 0x01
#define GIF_EXTENSION_APPLICATION 0xff
#define GIF_BLOCK_TERMINATOR 0x00
#define GIF_TRAILER 0x3b
/** standard GIF header size */
#define GIF_STANDARD_HEADER_SIZE 13
/**
* Updates the sprite memory size
*
* \param gif The animation context
* \param width The width of the sprite
* \param height The height of the sprite
* \return GIF_INSUFFICIENT_MEMORY for a memory error GIF_OK for success
*/
static gif_result
gif_initialise_sprite(gif_animation *gif,
unsigned int width,
unsigned int height)
{
unsigned int max_width;
unsigned int max_height;
struct bitmap *buffer;
/* Check if we've changed */
if ((width <= gif->width) && (height <= gif->height)) {
return GIF_OK;
}
/* Get our maximum values */
max_width = (width > gif->width) ? width : gif->width;
max_height = (height > gif->height) ? height : gif->height;
/* Allocate some more memory */
assert(gif->bitmap_callbacks.bitmap_create);
buffer = gif->bitmap_callbacks.bitmap_create(max_width, max_height);
if (buffer == NULL) {
return GIF_INSUFFICIENT_MEMORY;
}
assert(gif->bitmap_callbacks.bitmap_destroy);
gif->bitmap_callbacks.bitmap_destroy(gif->frame_image);
gif->frame_image = buffer;
gif->width = max_width;
gif->height = max_height;
/* Invalidate our currently decoded image */
gif->decoded_frame = GIF_INVALID_FRAME;
return GIF_OK;
}
/**
* Attempts to initialise the frame's extensions
*
* \param gif The animation context
* \param frame The frame number
* @return GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the
* frame GIF_OK for successful initialisation.
*/
static gif_result
gif_initialise_frame_extensions(gif_animation *gif, const int frame)
{
unsigned char *gif_data, *gif_end;
int gif_bytes;
unsigned int block_size;
/* Get our buffer position etc. */
gif_data = (unsigned char *)(gif->gif_data + gif->buffer_position);
gif_end = (unsigned char *)(gif->gif_data + gif->buffer_size);
/* Initialise the extensions */
while (gif_data < gif_end && gif_data[0] == GIF_EXTENSION_INTRODUCER) {
++gif_data;
if ((gif_bytes = (gif_end - gif_data)) < 1) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
/* Switch on extension label */
switch (gif_data[0]) {
case GIF_EXTENSION_GRAPHIC_CONTROL:
/* 6-byte Graphic Control Extension is:
*
* +0 CHAR Graphic Control Label
* +1 CHAR Block Size
* +2 CHAR __Packed Fields__
* 3BITS Reserved
* 3BITS Disposal Method
* 1BIT User Input Flag
* 1BIT Transparent Color Flag
* +3 SHORT Delay Time
* +5 CHAR Transparent Color Index
*/
if (gif_bytes < 6) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
gif->frames[frame].frame_delay = gif_data[3] | (gif_data[4] << 8);
if (gif_data[2] & GIF_TRANSPARENCY_MASK) {
gif->frames[frame].transparency = true;
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;
case GIF_EXTENSION_APPLICATION:
/* 14-byte+ Application Extension is:
*
* +0 CHAR Application Extension Label
* +1 CHAR Block Size
* +2 8CHARS Application Identifier
* +10 3CHARS Appl. Authentication Code
* +13 1-256 Application Data (Data sub-blocks)
*/
if (gif_bytes < 17) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
if ((gif_data[1] == 0x0b) &&
(strncmp((const char *) gif_data + 2,
"NETSCAPE2.0", 11) == 0) &&
(gif_data[13] == 0x03) &&
(gif_data[14] == 0x01)) {
gif->loop_count = gif_data[15] | (gif_data[16] << 8);
}
gif_data += (2 + gif_data[1]);
break;
case GIF_EXTENSION_COMMENT:
/* Move the pointer to the first data sub-block Skip 1
* byte for the extension label
*/
++gif_data;
break;
default:
/* Move the pointer to the first data sub-block Skip 2
* bytes for the extension label and size fields Skip
* the extension size itself
*/
if (gif_bytes < 2) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
gif_data += (2 + gif_data[1]);
}
/* Repeatedly skip blocks until we get a zero block or run out
* of data This data is ignored by this gif decoder
*/
gif_bytes = (gif_end - gif_data);
block_size = 0;
while (gif_data < gif_end && gif_data[0] != GIF_BLOCK_TERMINATOR) {
block_size = gif_data[0] + 1;
if ((gif_bytes -= block_size) < 0) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
gif_data += block_size;
}
++gif_data;
}
/* Set buffer position and return */
gif->buffer_position = (gif_data - gif->gif_data);
return GIF_OK;
}
/**
* Attempts to initialise the next frame
*
* \param gif The animation context
* \return error code
* - GIF_INSUFFICIENT_DATA for insufficient data to do anything
* - GIF_FRAME_DATA_ERROR for GIF frame data error
* - GIF_INSUFFICIENT_MEMORY for insufficient memory to process
* - GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the frame
* - GIF_DATA_ERROR for GIF error (invalid frame header)
* - GIF_OK for successful decoding
* - GIF_WORKING for successful decoding if more frames are expected
*/
static gif_result gif_initialise_frame(gif_animation *gif)
{
int frame;
gif_frame *temp_buf;
unsigned char *gif_data, *gif_end;
int gif_bytes;
unsigned int flags = 0;
unsigned int width, height, offset_x, offset_y;
unsigned int block_size, colour_table_size;
bool first_image = true;
gif_result return_value;
/* Get the frame to decode and our data position */
frame = gif->frame_count;
/* Get our buffer position etc. */
gif_data = (unsigned char *)(gif->gif_data + gif->buffer_position);
gif_end = (unsigned char *)(gif->gif_data + gif->buffer_size);
gif_bytes = (gif_end - gif_data);
/* Check if we've finished */
if ((gif_bytes > 0) && (gif_data[0] == GIF_TRAILER)) {
return GIF_OK;
}
/* Check if there is enough data remaining. The shortest block of data
* is a 4-byte comment extension + 1-byte block terminator + 1-byte gif
* trailer
*/
if (gif_bytes < 6) {
return GIF_INSUFFICIENT_DATA;
}
/* We could theoretically get some junk data that gives us millions of
* frames, so we ensure that we don't have a silly number
*/
if (frame > 4096) {
return GIF_FRAME_DATA_ERROR;
}
/* Get some memory to store our pointers in etc. */
if ((int)gif->frame_holders <= frame) {
/* Allocate more memory */
temp_buf = (gif_frame *)realloc(gif->frames, (frame + 1) * sizeof(gif_frame));
if (temp_buf == NULL) {
return GIF_INSUFFICIENT_MEMORY;
}
gif->frames = temp_buf;
gif->frame_holders = frame + 1;
}
/* Store our frame pointer. We would do it when allocating except we
* start off with one frame allocated so we can always use realloc.
*/
gif->frames[frame].frame_pointer = gif->buffer_position;
gif->frames[frame].display = false;
gif->frames[frame].virgin = true;
gif->frames[frame].disposal_method = 0;
gif->frames[frame].transparency = false;
gif->frames[frame].frame_delay = 100;
gif->frames[frame].redraw_required = false;
/* Invalidate any previous decoding we have of this frame */
if (gif->decoded_frame == frame) {
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 gif_decode_frame that doesn't have any of the LZW bits in
* it.
*/
/* Initialise any extensions */
gif->buffer_position = gif_data - gif->gif_data;
return_value = gif_initialise_frame_extensions(gif, frame);
if (return_value != GIF_OK) {
return return_value;
}
gif_data = (gif->gif_data + gif->buffer_position);
gif_bytes = (gif_end - gif_data);
/* Check if we've finished */
if ((gif_bytes = (gif_end - gif_data)) < 1) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
if (gif_data[0] == GIF_TRAILER) {
gif->buffer_position = (gif_data - gif->gif_data);
gif->frame_count = frame + 1;
return GIF_OK;
}
/* If we're not done, there should be an image descriptor */
if (gif_data[0] != GIF_IMAGE_SEPARATOR) {
return GIF_FRAME_DATA_ERROR;
}
/* Do some simple boundary checking */
if (gif_bytes < 10) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
offset_x = gif_data[1] | (gif_data[2] << 8);
offset_y = gif_data[3] | (gif_data[4] << 8);
width = gif_data[5] | (gif_data[6] << 8);
height = gif_data[7] | (gif_data[8] << 8);
/* Set up the redraw characteristics. We have to check for extending
* the area due to multi-image frames.
*/
if (!first_image) {
if (gif->frames[frame].redraw_x > offset_x) {
gif->frames[frame].redraw_width += (gif->frames[frame].redraw_x - offset_x);
gif->frames[frame].redraw_x = offset_x;
}
if (gif->frames[frame].redraw_y > offset_y) {
gif->frames[frame].redraw_height += (gif->frames[frame].redraw_y - offset_y);
gif->frames[frame].redraw_y = offset_y;
}
if ((offset_x + width) > (gif->frames[frame].redraw_x + gif->frames[frame].redraw_width)) {
gif->frames[frame].redraw_width = (offset_x + width) - gif->frames[frame].redraw_x;
}
if ((offset_y + height) > (gif->frames[frame].redraw_y + gif->frames[frame].redraw_height)) {
gif->frames[frame].redraw_height = (offset_y + height) - gif->frames[frame].redraw_y;
}
} else {
first_image = false;
gif->frames[frame].redraw_x = offset_x;
gif->frames[frame].redraw_y = offset_y;
gif->frames[frame].redraw_width = width;
gif->frames[frame].redraw_height = height;
}
/* 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_FRAME_CLEAR) ||
(gif->frames[frame].disposal_method == GIF_FRAME_RESTORE));
/* Boundary checking - shouldn't ever happen except with junk data */
if (gif_initialise_sprite(gif, (offset_x + width), (offset_y + height))) {
return GIF_INSUFFICIENT_MEMORY;
}
/* Decode the flags */
flags = gif_data[9];
colour_table_size = 2 << (flags & GIF_COLOUR_TABLE_SIZE_MASK);
/* Move our data onwards and remember we've got a bit of this frame */
gif_data += 10;
gif_bytes = (gif_end - gif_data);
gif->frame_count_partial = frame + 1;
/* Skip the local colour table */
if (flags & GIF_COLOUR_TABLE_MASK) {
gif_data += 3 * colour_table_size;
if ((gif_bytes = (gif_end - gif_data)) < 0) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
}
/* Ensure we have a correct code size */
if (gif_bytes < 1) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
if (gif_data[0] > LZW_CODE_MAX) {
return GIF_DATA_ERROR;
}
/* Move our pointer to the actual image data */
gif_data++;
--gif_bytes;
/* Repeatedly skip blocks until we get a zero block or run out of data
* These blocks of image data are processed later by gif_decode_frame()
*/
block_size = 0;
while (block_size != 1) {
if (gif_bytes < 1) return GIF_INSUFFICIENT_FRAME_DATA;
block_size = gif_data[0] + 1;
/* Check if the frame data runs off the end of the file */
if ((int)(gif_bytes - block_size) < 0) {
/* jcupitt 15/9/19
*
* There was code here to set a TRAILER tag. But this
* wrote to the input buffer, which will not work for
* libvips, where buffers can be mmaped read only files.
*
* Instead, just signal insufficient frame data.
*/
return GIF_INSUFFICIENT_FRAME_DATA;
} else {
gif_bytes -= block_size;
gif_data += block_size;
}
}
/* Add the frame and set the display flag */
gif->buffer_position = gif_data - gif->gif_data;
gif->frame_count = frame + 1;
gif->frames[frame].display = true;
/* Check if we've finished */
if (gif_bytes < 1) {
return GIF_INSUFFICIENT_FRAME_DATA;
} else {
if (gif_data[0] == GIF_TRAILER) {
return GIF_OK;
}
}
return GIF_WORKING;
}
/**
* Skips the frame's extensions (which have been previously initialised)
*
* \param gif The animation context
* \return GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the
* frame GIF_OK for successful decoding
*/
static gif_result gif_skip_frame_extensions(gif_animation *gif)
{
unsigned char *gif_data, *gif_end;
int gif_bytes;
unsigned int block_size;
/* Get our buffer position etc. */
gif_data = (unsigned char *)(gif->gif_data + gif->buffer_position);
gif_end = (unsigned char *)(gif->gif_data + gif->buffer_size);
gif_bytes = (gif_end - gif_data);
/* Skip the extensions */
while (gif_data < gif_end && gif_data[0] == GIF_EXTENSION_INTRODUCER) {
++gif_data;
if (gif_data >= gif_end) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
/* Switch on extension label */
switch(gif_data[0]) {
case GIF_EXTENSION_COMMENT:
/* Move the pointer to the first data sub-block
* 1 byte for the extension label
*/
++gif_data;
break;
default:
/* Move the pointer to the first data sub-block 2 bytes
* for the extension label and size fields Skip the
* extension size itself
*/
if (gif_data + 1 >= gif_end) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
gif_data += (2 + gif_data[1]);
}
/* Repeatedly skip blocks until we get a zero block or run out
* of data This data is ignored by this gif decoder
*/
gif_bytes = (gif_end - gif_data);
block_size = 0;
while (gif_data < gif_end && gif_data[0] != GIF_BLOCK_TERMINATOR) {
block_size = gif_data[0] + 1;
if ((gif_bytes -= block_size) < 0) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
gif_data += block_size;
}
++gif_data;
}
/* Set buffer position and return */
gif->buffer_position = (gif_data - gif->gif_data);
return GIF_OK;
}
static unsigned int gif_interlaced_line(int height, int y) {
if ((y << 3) < height) {
return (y << 3);
}
y -= ((height + 7) >> 3);
if ((y << 3) < (height - 4)) {
return (y << 3) + 4;
}
y -= ((height + 3) >> 3);
if ((y << 2) < (height - 2)) {
return (y << 2) + 2;
}
y -= ((height + 1) >> 2);
return (y << 1) + 1;
}
static gif_result gif_error_from_lzw(lzw_result l_res)
{
static const gif_result g_res[] = {
[LZW_OK] = GIF_OK,
[LZW_OK_EOD] = GIF_END_OF_FRAME,
[LZW_NO_MEM] = GIF_INSUFFICIENT_MEMORY,
[LZW_NO_DATA] = GIF_INSUFFICIENT_FRAME_DATA,
[LZW_EOI_CODE] = GIF_FRAME_DATA_ERROR,
[LZW_BAD_ICODE] = GIF_FRAME_DATA_ERROR,
[LZW_BAD_CODE] = GIF_FRAME_DATA_ERROR,
};
return g_res[l_res];
}
static void gif__record_previous_frame(gif_animation *gif)
{
bool need_alloc = gif->prev_frame == NULL;
const uint32_t *frame_data;
uint32_t *prev_frame;
if (gif->decoded_frame == GIF_INVALID_FRAME ||
gif->decoded_frame == gif->prev_index) {
/* No frame to copy, or already have this frame recorded. */
return;
}
assert(gif->bitmap_callbacks.bitmap_get_buffer);
frame_data = (void *)gif->bitmap_callbacks.bitmap_get_buffer(gif->frame_image);
if (!frame_data) {
return;
}
if (gif->prev_frame != NULL &&
gif->width * gif->height > gif->prev_width * gif->prev_height) {
need_alloc = true;
}
if (need_alloc) {
prev_frame = realloc(gif->prev_frame,
gif->width * gif->height * 4);
if (prev_frame == NULL) {
return;
}
} else {
prev_frame = gif->prev_frame;
}
memcpy(prev_frame, frame_data, gif->width * gif->height * 4);
gif->prev_frame = prev_frame;
gif->prev_width = gif->width;
gif->prev_height = gif->height;
gif->prev_index = gif->decoded_frame;
}
static gif_result gif__recover_previous_frame(const gif_animation *gif)
{
const uint32_t *prev_frame = gif->prev_frame;
unsigned height = gif->height < gif->prev_height ? gif->height : gif->prev_height;
unsigned width = gif->width < gif->prev_width ? gif->width : gif->prev_width;
uint32_t *frame_data;
if (prev_frame == NULL) {
return GIF_FRAME_DATA_ERROR;
}
assert(gif->bitmap_callbacks.bitmap_get_buffer);
frame_data = (void *)gif->bitmap_callbacks.bitmap_get_buffer(gif->frame_image);
if (!frame_data) {
return GIF_INSUFFICIENT_MEMORY;
}
for (unsigned y = 0; y < height; y++) {
memcpy(frame_data, prev_frame, width * 4);
frame_data += gif->width;
prev_frame += gif->prev_width;
}
return GIF_OK;
}
/**
* decode a gif frame
*
* \param gif gif animation context.
* \param frame The frame number to decode.
* \param clear_image flag for image data being cleared instead of plotted.
*/
static gif_result
gif_internal_decode_frame(gif_animation *gif,
unsigned int frame,
bool clear_image)
{
gif_result err;
unsigned int index = 0;
unsigned char *gif_data, *gif_end;
int gif_bytes;
unsigned int width, height, offset_x, offset_y;
unsigned int flags, colour_table_size, interlace;
unsigned int *colour_table;
unsigned int *frame_data = 0; // Set to 0 for no warnings
unsigned int *frame_scanline;
unsigned int save_buffer_position;
unsigned int return_value = 0;
unsigned int x, y, decode_y, burst_bytes;
register unsigned char colour;
/* Ensure this frame is supposed to be decoded */
if (gif->frames[frame].display == false) {
return GIF_OK;
}
/* Ensure the frame is in range to decode */
if (frame > gif->frame_count_partial) {
return GIF_INSUFFICIENT_DATA;
}
/* done if frame is already decoded */
if ((!clear_image) &&
((int)frame == gif->decoded_frame)) {
return GIF_OK;
}
/* Get the start of our frame data and the end of the GIF data */
gif_data = gif->gif_data + gif->frames[frame].frame_pointer;
gif_end = gif->gif_data + gif->buffer_size;
gif_bytes = (gif_end - gif_data);
/*
* Ensure there is a minimal amount of data to proceed. The shortest
* block of data is a 10-byte image descriptor + 1-byte gif trailer
*/
if (gif_bytes < 12) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
/* Save the buffer position */
save_buffer_position = gif->buffer_position;
gif->buffer_position = gif_data - gif->gif_data;
/* Skip any extensions because they have allready been processed */
if ((return_value = gif_skip_frame_extensions(gif)) != GIF_OK) {
goto gif_decode_frame_exit;
}
gif_data = (gif->gif_data + gif->buffer_position);
gif_bytes = (gif_end - gif_data);
/* Ensure we have enough data for the 10-byte image descriptor + 1-byte
* gif trailer
*/
if (gif_bytes < 12) {
return_value = GIF_INSUFFICIENT_FRAME_DATA;
goto gif_decode_frame_exit;
}
/* 10-byte Image Descriptor is:
*
* +0 CHAR Image Separator (0x2c)
* +1 SHORT Image Left Position
* +3 SHORT Image Top Position
* +5 SHORT Width
* +7 SHORT Height
* +9 CHAR __Packed Fields__
* 1BIT Local Colour Table Flag
* 1BIT Interlace Flag
* 1BIT Sort Flag
* 2BITS Reserved
* 3BITS Size of Local Colour Table
*/
if (gif_data[0] != GIF_IMAGE_SEPARATOR) {
return_value = GIF_DATA_ERROR;
goto gif_decode_frame_exit;
}
offset_x = gif_data[1] | (gif_data[2] << 8);
offset_y = gif_data[3] | (gif_data[4] << 8);
width = gif_data[5] | (gif_data[6] << 8);
height = gif_data[7] | (gif_data[8] << 8);
/* Boundary checking - shouldn't ever happen except unless the data has
* been modified since initialisation.
*/
if ((offset_x + width > gif->width) ||
(offset_y + height > gif->height)) {
return_value = GIF_DATA_ERROR;
goto gif_decode_frame_exit;
}
/* Decode the flags */
flags = gif_data[9];
colour_table_size = 2 << (flags & GIF_COLOUR_TABLE_SIZE_MASK);
interlace = flags & GIF_INTERLACE_MASK;
/* Advance data pointer to next block either colour table or image
* data.
*/
gif_data += 10;
gif_bytes = (gif_end - gif_data);
/* Set up the colour table */
if (flags & GIF_COLOUR_TABLE_MASK) {
if (gif_bytes < (int)(3 * colour_table_size)) {
return_value = GIF_INSUFFICIENT_FRAME_DATA;
goto gif_decode_frame_exit;
}
colour_table = gif->local_colour_table;
if (!clear_image) {
for (index = 0; index < colour_table_size; index++) {
/* Gif colour map contents are r,g,b.
*
* We want to pack them bytewise into the
* colour table, such that the red component
* is in byte 0 and the alpha component is in
* byte 3.
*/
unsigned char *entry =
(unsigned char *) &colour_table[index];
entry[0] = gif_data[0]; /* r */
entry[1] = gif_data[1]; /* g */
entry[2] = gif_data[2]; /* b */
entry[3] = 0xff; /* a */
gif_data += 3;
}
} else {
gif_data += 3 * colour_table_size;
}
gif_bytes = (gif_end - gif_data);
} else {
colour_table = gif->global_colour_table;
}
/* Ensure sufficient data remains */
if (gif_bytes < 1) {
return_value = GIF_INSUFFICIENT_FRAME_DATA;
goto gif_decode_frame_exit;
}
/* check for an end marker */
if (gif_data[0] == GIF_TRAILER) {
return_value = GIF_OK;
goto gif_decode_frame_exit;
}
/* Get the frame data */
assert(gif->bitmap_callbacks.bitmap_get_buffer);
frame_data = (void *)gif->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) {
lzw_result res;
const uint8_t *stack_base;
const uint8_t *stack_pos;
/* Ensure we have enough data for a 1-byte LZW code size +
* 1-byte gif trailer
*/
if (gif_bytes < 2) {
return_value = GIF_INSUFFICIENT_FRAME_DATA;
goto gif_decode_frame_exit;
}
/* If we only have a 1-byte LZW code size + 1-byte gif trailer,
* we're finished
*/
if ((gif_bytes == 2) && (gif_data[1] == GIF_TRAILER)) {
return_value = GIF_OK;
goto gif_decode_frame_exit;
}
/* 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,
GIF_TRANSPARENT_COLOUR,
gif->width * gif->height * sizeof(int));
gif->decoded_frame = frame;
/* The line below would fill the image with its
* background color, but because GIFs support
* transparency we likely wouldn't want to do that. */
/* memset((char*)frame_data, colour_table[gif->background_index], gif->width * gif->height * sizeof(int)); */
} else if ((frame != 0) &&
(gif->frames[frame - 1].disposal_method == GIF_FRAME_CLEAR)) {
return_value = gif_internal_decode_frame(gif,
(frame - 1),
true);
if (return_value != GIF_OK) {
goto gif_decode_frame_exit;
}
} else if ((frame != 0) &&
(gif->frames[frame - 1].disposal_method == GIF_FRAME_RESTORE)) {
/*
* If the previous frame's disposal method requires we
* restore the previous image, restore our saved image.
*/
err = gif__recover_previous_frame(gif);
if (err != GIF_OK) {
/* see notes above on transparency
* vs. background color
*/
memset((char*)frame_data,
GIF_TRANSPARENT_COLOUR,
gif->width * gif->height * sizeof(int));
}
}
if (gif->frames[frame].disposal_method == GIF_FRAME_RESTORE) {
/* Store the previous frame for later restoration */
gif__record_previous_frame(gif);
}
gif->decoded_frame = frame;
gif->buffer_position = (gif_data - gif->gif_data) + 1;
/* Initialise the LZW decoding */
res = lzw_decode_init(gif->lzw_ctx, gif->gif_data,
gif->buffer_size, gif->buffer_position,
gif_data[0], &stack_base, &stack_pos);
if (res != LZW_OK) {
return gif_error_from_lzw(res);
}
/* Decompress the data */
for (y = 0; y < height; y++) {
if (interlace) {
decode_y = gif_interlaced_line(height, y) + offset_y;
} else {
decode_y = y + offset_y;
}
frame_scanline = frame_data + offset_x + (decode_y * gif->width);
/* Rather than decoding pixel by pixel, we try to burst
* out streams of data to remove the need for end-of
* data checks every pixel.
*/
x = width;
while (x > 0) {
burst_bytes = (stack_pos - stack_base);
if (burst_bytes > 0) {
if (burst_bytes > x) {
burst_bytes = x;
}
x -= burst_bytes;
while (burst_bytes-- > 0) {
colour = *--stack_pos;
if (((gif->frames[frame].transparency) &&
(colour != gif->frames[frame].transparency_index)) ||
(!gif->frames[frame].transparency)) {
*frame_scanline = colour_table[colour];
}
frame_scanline++;
}
} else {
res = lzw_decode(gif->lzw_ctx, &stack_pos);
if (res != LZW_OK) {
/* Unexpected end of frame, try to recover */
if (res == LZW_OK_EOD) {
return_value = GIF_OK;
} else {
return_value = gif_error_from_lzw(res);
}
goto gif_decode_frame_exit;
}
}
}
}
} else {
/* Clear our frame */
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);
if (gif->frames[frame].transparency) {
memset(frame_scanline,
GIF_TRANSPARENT_COLOUR,
width * 4);
} else {
memset(frame_scanline,
colour_table[gif->background_index],
width * 4);
}
}
}
}
gif_decode_frame_exit:
/* Check if we should test for optimisation */
if (gif->frames[frame].virgin) {
if (gif->bitmap_callbacks.bitmap_test_opaque) {
gif->frames[frame].opaque = gif->bitmap_callbacks.bitmap_test_opaque(gif->frame_image);
} else {
gif->frames[frame].opaque = false;
}
gif->frames[frame].virgin = false;
}
if (gif->bitmap_callbacks.bitmap_set_opaque) {
gif->bitmap_callbacks.bitmap_set_opaque(gif->frame_image, gif->frames[frame].opaque);
}
if (gif->bitmap_callbacks.bitmap_modified) {
gif->bitmap_callbacks.bitmap_modified(gif->frame_image);
}
/* Restore the buffer position */
gif->buffer_position = save_buffer_position;
return return_value;
}
/* exported function documented in libnsgif.h */
void gif_create(gif_animation *gif, gif_bitmap_callback_vt *bitmap_callbacks)
{
memset(gif, 0, sizeof(gif_animation));
gif->bitmap_callbacks = *bitmap_callbacks;
gif->decoded_frame = GIF_INVALID_FRAME;
gif->prev_index = GIF_INVALID_FRAME;
}
/* exported function documented in libnsgif.h */
gif_result gif_initialise(gif_animation *gif, size_t size, unsigned char *data)
{
unsigned char *gif_data;
unsigned int index;
gif_result return_value;
/* Initialize values */
gif->buffer_size = size;
gif->gif_data = data;
if (gif->lzw_ctx == NULL) {
lzw_result res = lzw_context_create(
(struct lzw_ctx **)&gif->lzw_ctx);
if (res != LZW_OK) {
return gif_error_from_lzw(res);
}
}
/* Check for sufficient data to be a GIF (6-byte header + 7-byte
* logical screen descriptor)
*/
if (gif->buffer_size < GIF_STANDARD_HEADER_SIZE) {
return GIF_INSUFFICIENT_DATA;
}
/* Get our current processing position */
gif_data = gif->gif_data + gif->buffer_position;
/* See if we should initialise the GIF */
if (gif->buffer_position == 0) {
/* We want everything to be NULL before we start so we've no
* chance of freeing bad pointers (paranoia)
*/
gif->frame_image = NULL;
gif->frames = NULL;
gif->local_colour_table = NULL;
gif->global_colour_table = NULL;
/* The caller may have been lazy and not reset any values */
gif->frame_count = 0;
gif->frame_count_partial = 0;
gif->decoded_frame = GIF_INVALID_FRAME;
/* 6-byte GIF file header is:
*
* +0 3CHARS Signature ('GIF')
* +3 3CHARS Version ('87a' or '89a')
*/
if (strncmp((const char *) gif_data, "GIF", 3) != 0) {
return GIF_DATA_ERROR;
}
gif_data += 3;
/* Ensure GIF reports version 87a or 89a */
/*
if ((strncmp(gif_data, "87a", 3) != 0) &&
(strncmp(gif_data, "89a", 3) != 0))
LOG(("Unknown GIF format - proceeding anyway"));
*/
gif_data += 3;
/* 7-byte Logical Screen Descriptor is:
*
* +0 SHORT Logical Screen Width
* +2 SHORT Logical Screen Height
* +4 CHAR __Packed Fields__
* 1BIT Global Colour Table Flag
* 3BITS Colour Resolution
* 1BIT Sort Flag
* 3BITS Size of Global Colour Table
* +5 CHAR Background Colour Index
* +6 CHAR Pixel Aspect Ratio
*/
gif->width = gif_data[0] | (gif_data[1] << 8);
gif->height = gif_data[2] | (gif_data[3] << 8);
gif->global_colours = (gif_data[4] & GIF_COLOUR_TABLE_MASK);
gif->colour_table_size = (2 << (gif_data[4] & GIF_COLOUR_TABLE_SIZE_MASK));
gif->background_index = gif_data[5];
gif->aspect_ratio = gif_data[6];
gif->loop_count = 1;
gif_data += 7;
/* Some broken GIFs report the size as the screen size they
* were created in. As such, we detect for the common cases and
* set the sizes as 0 if they are found which results in the
* GIF being the maximum size of the frames.
*/
if (((gif->width == 640) && (gif->height == 480)) ||
((gif->width == 640) && (gif->height == 512)) ||
((gif->width == 800) && (gif->height == 600)) ||
((gif->width == 1024) && (gif->height == 768)) ||
((gif->width == 1280) && (gif->height == 1024)) ||
((gif->width == 1600) && (gif->height == 1200)) ||
((gif->width == 0) || (gif->height == 0)) ||
((gif->width > 2048) || (gif->height > 2048))) {
gif->width = 1;
gif->height = 1;
}
/* Allocate some data irrespective of whether we've got any
* colour tables. We always get the maximum size in case a GIF
* is lying to us. It's far better to give the wrong colours
* than to trample over some memory somewhere.
*/
gif->global_colour_table = calloc(GIF_MAX_COLOURS, sizeof(unsigned int));
gif->local_colour_table = calloc(GIF_MAX_COLOURS, sizeof(unsigned int));
if ((gif->global_colour_table == NULL) ||
(gif->local_colour_table == NULL)) {
gif_finalise(gif);
return GIF_INSUFFICIENT_MEMORY;
}
/* Set the first colour to a value that will never occur in
* reality so we know if we've processed it
*/
gif->global_colour_table[0] = GIF_PROCESS_COLOURS;
/* Check if the GIF has no frame data (13-byte header + 1-byte
* termination block) Although generally useless, the GIF
* specification does not expressly prohibit this
*/
if (gif->buffer_size == (GIF_STANDARD_HEADER_SIZE + 1)) {
if (gif_data[0] == GIF_TRAILER) {
return GIF_OK;
} else {
return GIF_INSUFFICIENT_DATA;
}
}
/* Initialise enough workspace for a frame */
if ((gif->frames = (gif_frame *)malloc(sizeof(gif_frame))) == NULL) {
gif_finalise(gif);
return GIF_INSUFFICIENT_MEMORY;
}
gif->frame_holders = 1;
/* Initialise the bitmap header */
assert(gif->bitmap_callbacks.bitmap_create);
gif->frame_image = gif->bitmap_callbacks.bitmap_create(gif->width, gif->height);
if (gif->frame_image == NULL) {
gif_finalise(gif);
return GIF_INSUFFICIENT_MEMORY;
}
/* Remember we've done this now */
gif->buffer_position = gif_data - gif->gif_data;
}
/* Do the colour map if we haven't already. As the top byte is always
* 0xff or 0x00 depending on the transparency we know if it's been
* filled in.
*/
if (gif->global_colour_table[0] == GIF_PROCESS_COLOURS) {
/* Check for a global colour map signified by bit 7 */
if (gif->global_colours) {
if (gif->buffer_size < (gif->colour_table_size * 3 + GIF_STANDARD_HEADER_SIZE)) {
return GIF_INSUFFICIENT_DATA;
}
for (index = 0; index < gif->colour_table_size; index++) {
/* Gif colour map contents are r,g,b.
*
* We want to pack them bytewise into the
* colour table, such that the red component
* is in byte 0 and the alpha component is in
* byte 3.
*/
unsigned char *entry = (unsigned char *) &gif->
global_colour_table[index];
entry[0] = gif_data[0]; /* r */
entry[1] = gif_data[1]; /* g */
entry[2] = gif_data[2]; /* b */
entry[3] = 0xff; /* a */
gif_data += 3;
}
gif->buffer_position = (gif_data - gif->gif_data);
} else {
/* Create a default colour table with the first two
* colours as black and white
*/
unsigned int *entry = gif->global_colour_table;
entry[0] = 0x00000000;
/* Force Alpha channel to opaque */
((unsigned char *) entry)[3] = 0xff;
entry[1] = 0xffffffff;
}
}
/* Repeatedly try to initialise frames */
while ((return_value = gif_initialise_frame(gif)) == GIF_WORKING);
/* If there was a memory error tell the caller */
if ((return_value == GIF_INSUFFICIENT_MEMORY) ||
(return_value == GIF_DATA_ERROR)) {
return return_value;
}
/* If we didn't have some frames then a GIF_INSUFFICIENT_DATA becomes a
* GIF_INSUFFICIENT_FRAME_DATA
*/
if ((return_value == GIF_INSUFFICIENT_DATA) &&
(gif->frame_count_partial > 0)) {
return GIF_INSUFFICIENT_FRAME_DATA;
}
/* Return how many we got */
return return_value;
}
/* exported function documented in libnsgif.h */
gif_result gif_decode_frame(gif_animation *gif, unsigned int frame)
{
return gif_internal_decode_frame(gif, frame, false);
}
/* exported function documented in libnsgif.h */
void gif_finalise(gif_animation *gif)
{
/* Release all our memory blocks */
if (gif->frame_image) {
assert(gif->bitmap_callbacks.bitmap_destroy);
gif->bitmap_callbacks.bitmap_destroy(gif->frame_image);
}
gif->frame_image = NULL;
free(gif->frames);
gif->frames = NULL;
free(gif->local_colour_table);
gif->local_colour_table = NULL;
free(gif->global_colour_table);
gif->global_colour_table = NULL;
free(gif->prev_frame);
gif->prev_frame = NULL;
lzw_context_destroy(gif->lzw_ctx);
gif->lzw_ctx = NULL;
}
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