/* * Copyright 2004 Richard Wilson * Copyright 2008 Sean Fox * * 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 #include #include #include #include #include #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) { /* 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; } /** * 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, [LZW_BAD_DATA] = GIF_FRAME_DATA_ERROR, }; return g_res[l_res]; } /** * 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) { 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, find the last image set * to "do not dispose" and get that frame data */ int last_undisposed_frame = frame - 2; while ((last_undisposed_frame >= 0) && (gif->frames[last_undisposed_frame].disposal_method == GIF_FRAME_RESTORE)) { last_undisposed_frame--; } /* 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 { return_value = gif_internal_decode_frame(gif, last_undisposed_frame, false); if (return_value != GIF_OK) { goto gif_decode_frame_exit; } /* Get this frame's 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; } } } 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; } /* 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; lzw_context_destroy(gif->lzw_ctx); gif->lzw_ctx = NULL; }