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Diffstat (limited to 'src/libnsgif.c')
| -rw-r--r-- | src/libnsgif.c | 1260 |
1 files changed, 1260 insertions, 0 deletions
diff --git a/src/libnsgif.c b/src/libnsgif.c new file mode 100644 index 0000000..1eb46c5 --- /dev/null +++ b/src/libnsgif.c @@ -0,0 +1,1260 @@ +/* + * 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 <stdio.h> +#include <string.h> +#include <stdlib.h> +#include <assert.h> +#include "libnsgif.h" +#include "utils/log.h" + +/* READING GIF FILES + ================= + + The functions provided by this file allow for efficient progressive GIF + decoding. Whilst the initialisation does not ensure that there is + sufficient image data to complete the entire frame, it does ensure that + the information provided is valid. Any subsequent attempts to decode an + initialised GIF are guaranteed to succeed, and any bytes of the image + not present are assumed to be totally transparent. + + To begin decoding a GIF, the 'gif' structure must be initialised with + the 'gif_data' and 'buffer_size' set to their initial values. The + 'buffer_position' should initially be 0, and will be internally updated + as the decoding commences. The caller should then repeatedly call + gif_initialise() with the structure until the function returns 1, or + no more data is avaliable. + + Once the initialisation has begun, the decoder completes the variables + 'frame_count' and 'frame_count_partial'. The former being the total + number of frames that have been successfully initialised, and the + latter being the number of frames that a partial amount of data is + available for. This assists the caller in managing the animation whilst + decoding is continuing. + + To decode a frame, the caller must use gif_decode_frame() which updates + the current 'frame_image' to reflect the desired frame. The required + 'disposal_method' is also updated to reflect how the frame should be + plotted. The caller must not assume that the current 'frame_image' will + be valid between calls if initialisation is still occuring, and should + either always request that the frame is decoded (no processing will + occur if the 'decoded_frame' has not been invalidated by initialisation) + or perform the check itself. + + It should be noted that gif_finalise() should always be called, even if + no frames were initialised. Additionally, it is the responsibility of + the caller to free 'gif_data'. + + [rjw] - Fri 2nd April 2004 +*/ + +/* TO-DO LIST + ================= + + + Plain text and comment extensions could be implemented if there is any + interest in doing so. +*/ + + + + +/* 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 + +/* Maximum LZW bits available +*/ +#define GIF_MAX_LZW 12 + +/* 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 + +/* Internal GIF routines +*/ +static gif_result gif_initialise_sprite(gif_animation *gif, unsigned int width, unsigned int height); +static gif_result gif_initialise_frame(gif_animation *gif); +static gif_result gif_initialise_frame_extensions(gif_animation *gif, const int frame); +static gif_result gif_skip_frame_extensions(gif_animation *gif); +static unsigned int gif_interlaced_line(int height, int y); + + + +/* Internal LZW routines +*/ +static void gif_init_LZW(gif_animation *gif); +static bool gif_next_LZW(gif_animation *gif); +static int gif_next_code(gif_animation *gif, int code_size); + +/* General LZW values. They are shared for all GIFs being decoded, and + thus we can't handle progressive decoding efficiently without having + the data for each image which would use an extra 10Kb or so per GIF. +*/ +static unsigned char buf[4]; +static unsigned char *direct; +static int maskTbl[16] = {0x0000, 0x0001, 0x0003, 0x0007, 0x000f, 0x001f, 0x003f, 0x007f, + 0x00ff, 0x01ff, 0x03ff, 0x07ff, 0x0fff, 0x1fff, 0x3fff, 0x7fff}; +static int table[2][(1 << GIF_MAX_LZW)]; +static unsigned char stack[(1 << GIF_MAX_LZW) * 2]; +static unsigned char *stack_pointer; +static int code_size, set_code_size; +static int max_code, max_code_size; +static int clear_code, end_code; +static int curbit, lastbit, last_byte; +static int firstcode, oldcode; +static bool zero_data_block = false; +static bool get_done; + +/* Whether to clear the decoded image rather than plot +*/ +static bool clear_image = false; + + + +/** Initialises necessary gif_animation members. +*/ +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; +} + + +/** Initialises any workspace held by the animation and attempts to decode + any information that hasn't already been decoded. + If an error occurs, all previously decoded frames are retained. + + @return GIF_FRAME_DATA_ERROR for GIF frame data error + GIF_INSUFFICIENT_FRAME_DATA for insufficient data to process + any more frames + GIF_INSUFFICIENT_MEMORY for memory error + GIF_DATA_ERROR for GIF error + GIF_INSUFFICIENT_DATA for insufficient data to do anything + GIF_OK for successful decoding + GIF_WORKING for successful decoding if more frames are expected +*/ +gif_result gif_initialise(gif_animation *gif, size_t size, unsigned char *data) { + unsigned char *gif_data; + unsigned int index; + gif_result return_value; + + /* The GIF format is thoroughly documented; a full description + * can be found at http://www.w3.org/Graphics/GIF/spec-gif89a.txt + */ + + /* Initialize values + */ + gif->buffer_size = size; + gif->gif_data = data; + + /* Check for sufficient data to be a GIF (6-byte header + 7-byte logical screen descriptor) + */ + if (gif->buffer_size < 13) 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 = (unsigned int *)calloc(GIF_MAX_COLOURS, sizeof(int)); + gif->local_colour_table = (unsigned int *)calloc(GIF_MAX_COLOURS, sizeof(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 == 14) { + if (gif_data[0] == GIF_TRAILER) + return GIF_OK; + else + return GIF_INSUFFICIENT_DATA; + } + + /* Initialise enough workspace for 4 frames initially + */ + if ((gif->frames = (gif_frame *)malloc(sizeof(gif_frame))) == NULL) { + gif_finalise(gif); + return GIF_INSUFFICIENT_MEMORY; + } + gif->frame_holders = 1; + + /* Initialise the sprite header + */ + assert(gif->bitmap_callbacks.bitmap_create); + if ((gif->frame_image = gif->bitmap_callbacks.bitmap_create(gif->width, gif->height)) == 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 + 12)) { + return GIF_INSUFFICIENT_DATA; + } + for (index = 0; index < gif->colour_table_size; index++) { + char colour[] = {0, 0, 0, (char)0xff}; + colour[0] = gif_data[0]; + colour[1] = gif_data[1]; + colour[2] = gif_data[2]; + gif->global_colour_table[index] = *((int *) colour); + 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 + */ + gif->global_colour_table[0] = 0xff000000; + gif->global_colour_table[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; +} + + +/** Updates the sprite memory size + + @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); + if ((buffer = gif->bitmap_callbacks.bitmap_create(max_width, max_height)) == 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 next frame + + @return 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 we have enough data + * 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 + */ + if ((temp_buf = (gif_frame *)realloc(gif->frames, + (frame + 1) * sizeof(gif_frame))) == 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; + if ((return_value = gif_initialise_frame_extensions(gif, frame)) != 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; + else 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 + */ + 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_data[0] > GIF_MAX_LZW) + return GIF_DATA_ERROR; + + /* Move our pointer to the actual image data + */ + gif_data++; + if (--gif_bytes < 0) + return GIF_INSUFFICIENT_FRAME_DATA; + + /* 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) { + 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) { + /* Try to recover by signaling the end of the gif. + * Once we get garbage data, there is no logical + * way to determine where the next frame is. + * It's probably better to partially load the gif + * than not at all. + */ + if (gif_bytes >= 2) { + gif_data[0] = 0; + gif_data[1] = GIF_TRAILER; + gif_bytes = 1; + ++gif_data; + break; + } else + 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; +} + +/** Attempts to initialise the frame's extensions + + @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[0] == GIF_EXTENSION_INTRODUCER) { + ++gif_data; + gif_bytes = (gif_end - gif_data); + + /* Switch on extension label + */ + switch(gif_data[0]) { + /* 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 + */ + case GIF_EXTENSION_GRAPHIC_CONTROL: + 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; + + /* 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) + */ + case GIF_EXTENSION_APPLICATION: + 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; + + /* Move the pointer to the first data sub-block + * Skip 1 byte for the extension label + */ + case GIF_EXTENSION_COMMENT: + ++gif_data; + break; + + /* Move the pointer to the first data sub-block + * Skip 2 bytes for the extension label and size fields + * Skip the extension size itself + */ + default: + 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[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; +} + + +/** Decodes a GIF frame. + + @return GIF_FRAME_DATA_ERROR for GIF frame data error + GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the frame + GIF_DATA_ERROR for GIF error (invalid frame header) + GIF_INSUFFICIENT_DATA for insufficient data to do anything + GIF_INSUFFICIENT_MEMORY for insufficient memory to process + GIF_OK for successful decoding + If a frame does not contain any image data, GIF_OK is returned and + gif->current_error is set to GIF_FRAME_NO_DISPLAY +*/ +gif_result gif_decode_frame(gif_animation *gif, unsigned int frame) { + 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; + int last_undisposed_frame = (frame - 1); + register unsigned char colour; + + /* Ensure this frame is supposed to be decoded + */ + if (gif->frames[frame].display == false) { + gif->current_error = GIF_FRAME_NO_DISPLAY; + return GIF_OK; + } + + /* Ensure we have a frame to decode + */ + if (frame > gif->frame_count_partial) + return GIF_INSUFFICIENT_DATA; + 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); + + /* Check if we have enough data + * 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 we all ready processed them + */ + 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; + + /* Move our pointer to the colour table or image data (if no colour table is given) + */ + 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++) { + char colour[] = {0, 0, 0, (char)0xff}; + colour[0] = gif_data[0]; + colour[1] = gif_data[1]; + colour[2] = gif_data[2]; + colour_table[index] = *((int *) colour); + gif_data += 3; + } + } else { + gif_data += 3 * colour_table_size; + } + gif_bytes = (gif_end - gif_data); + } else { + colour_table = gif->global_colour_table; + } + + /* Check if we've finished + */ + if (gif_bytes < 1) { + return_value = GIF_INSUFFICIENT_FRAME_DATA; + goto gif_decode_frame_exit; + } else 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 = (unsigned int *)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) { + /* 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 + */ + } else 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)) { + clear_image = true; + if ((return_value = gif_decode_frame(gif, (frame - 1))) != 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 + */ + } 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) { + /* see notes above on transparency vs. background color */ + memset((char*)frame_data, GIF_TRANSPARENT_COLOUR, gif->width * gif->height * sizeof(int)); + } else { + if ((return_value = gif_decode_frame(gif, last_undisposed_frame)) != GIF_OK) + goto gif_decode_frame_exit; + /* Get this frame's data + */ + assert(gif->bitmap_callbacks.bitmap_get_buffer); + frame_data = (unsigned int *)gif->bitmap_callbacks.bitmap_get_buffer(gif->frame_image); + if (!frame_data) + return GIF_INSUFFICIENT_MEMORY; + } + } + gif->decoded_frame = frame; + + /* Initialise the LZW decoding + */ + set_code_size = gif_data[0]; + gif->buffer_position = (gif_data - gif->gif_data) + 1; + + /* Set our code variables + */ + code_size = set_code_size + 1; + clear_code = (1 << set_code_size); + end_code = clear_code + 1; + max_code_size = clear_code << 1; + max_code = clear_code + 2; + curbit = lastbit = 0; + last_byte = 2; + get_done = false; + direct = buf; + gif_init_LZW(gif); + + /* 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_pointer - stack); + if (burst_bytes > 0) { + if (burst_bytes > x) + burst_bytes = x; + x -= burst_bytes; + while (burst_bytes-- > 0) { + colour = *--stack_pointer; + if (((gif->frames[frame].transparency) && + (colour != gif->frames[frame].transparency_index)) || + (!gif->frames[frame].transparency)) + *frame_scanline = colour_table[colour]; + frame_scanline++; + } + } else { + if (!gif_next_LZW(gif)) { + /* Unexpected end of frame, try to recover + */ + if (gif->current_error == GIF_END_OF_FRAME) + return_value = GIF_OK; + else + return_value = gif->current_error; + 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; + + /* Success! + */ + return return_value; + +} + +/** Skips the frame's extensions (which have been previously initialised) + + @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[0] == GIF_EXTENSION_INTRODUCER) { + ++gif_data; + + /* Switch on extension label + */ + switch(gif_data[0]) { + /* Move the pointer to the first data sub-block + * 1 byte for the extension label + */ + case GIF_EXTENSION_COMMENT: + ++gif_data; + break; + + /* Move the pointer to the first data sub-block + * 2 bytes for the extension label and size fields + * Skip the extension size itself + */ + default: + 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[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; +} + +/* Releases any workspace held by the animation +*/ +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; +} + +/** + * Initialise LZW decoding + */ +void gif_init_LZW(gif_animation *gif) { + int i; + + gif->current_error = 0; + if (clear_code >= (1 << GIF_MAX_LZW)) { + stack_pointer = stack; + gif->current_error = GIF_FRAME_DATA_ERROR; + return; + } + + /* initialise our table */ + memset(table, 0x00, (1 << GIF_MAX_LZW) * 8); + for (i = 0; i < clear_code; ++i) + table[1][i] = i; + + /* update our LZW parameters */ + code_size = set_code_size + 1; + max_code_size = clear_code << 1; + max_code = clear_code + 2; + stack_pointer = stack; + do { + firstcode = oldcode = gif_next_code(gif, code_size); + } while (firstcode == clear_code); + *stack_pointer++ =firstcode; +} + + +static bool gif_next_LZW(gif_animation *gif) { + int code, incode; + int block_size; + int new_code; + + code = gif_next_code(gif, code_size); + if (code < 0) { + gif->current_error = code; + return false; + } else if (code == clear_code) { + gif_init_LZW(gif); + return true; + } else if (code == end_code) { + /* skip to the end of our data so multi-image GIFs work */ + if (zero_data_block) { + gif->current_error = GIF_FRAME_DATA_ERROR; + return false; + } + block_size = 0; + while (block_size != 1) { + block_size = gif->gif_data[gif->buffer_position] + 1; + gif->buffer_position += block_size; + } + gif->current_error = GIF_FRAME_DATA_ERROR; + return false; + } + + incode = code; + if (code >= max_code) { + *stack_pointer++ = firstcode; + code = oldcode; + } + + /* The following loop is the most important in the GIF decoding cycle as every + * single pixel passes through it. + * + * Note: our stack is always big enough to hold a complete decompressed chunk. */ + while (code >= clear_code) { + *stack_pointer++ = table[1][code]; + new_code = table[0][code]; + if (new_code < clear_code) { + code = new_code; + break; + } + *stack_pointer++ = table[1][new_code]; + code = table[0][new_code]; + if (code == new_code) { + gif->current_error = GIF_FRAME_DATA_ERROR; + return false; + } + } + + *stack_pointer++ = firstcode = table[1][code]; + + if ((code = max_code) < (1 << GIF_MAX_LZW)) { + table[0][code] = oldcode; + table[1][code] = firstcode; + ++max_code; + if ((max_code >= max_code_size) && (max_code_size < (1 << GIF_MAX_LZW))) { + max_code_size = max_code_size << 1; + ++code_size; + } + } + oldcode = incode; + return true; +} + +static int gif_next_code(gif_animation *gif, int code_size) { + int i, j, end, count, ret; + unsigned char *b; + + end = curbit + code_size; + if (end >= lastbit) { + if (get_done) + return GIF_END_OF_FRAME; + buf[0] = direct[last_byte - 2]; + buf[1] = direct[last_byte - 1]; + + /* get the next block */ + direct = gif->gif_data + gif->buffer_position; + zero_data_block = ((count = direct[0]) == 0); + if ((gif->buffer_position + count) >= gif->buffer_size) + return GIF_INSUFFICIENT_FRAME_DATA; + if (count == 0) + get_done = true; + else { + direct -= 1; + buf[2] = direct[2]; + buf[3] = direct[3]; + } + gif->buffer_position += count + 1; + + /* update our variables */ + last_byte = 2 + count; + curbit = (curbit - lastbit) + 16; + lastbit = (2 + count) << 3; + end = curbit + code_size; + } + + i = curbit >> 3; + if (i < 2) + b = buf; + else + b = direct; + + ret = b[i]; + j = (end >> 3) - 1; + if (i <= j) { + ret |= (b[i + 1] << 8); + if (i < j) + ret |= (b[i + 2] << 16); + } + ret = (ret >> (curbit % 8)) & maskTbl[code_size]; + curbit += code_size; + return ret; +} |