gif_writer.c File Reference

Implementations of custom LZW animated GIF writing utilities. More...

#include "gif_writer.h"

Data Structures
struct	GifBitWriter

Macros
#define	GIF_COMPAT_MIN_FAST_DELAY_CS   5

Typedefs
typedef struct GifBitWriter	GifBitWriter

Functions
static void	WriteU16 (FILE *f, int value)
	Writes a 16-bit unsigned integer in little-endian format to a file stream. More...
static void	ResolveCompatibleTiming (int requested_delay_cs, int *out_frame_step, int *out_delay_cs)
	Resolves compatible delay timing constraints to prevent browser lag. More...
static int	ColorTableSize (int color_count)
	Computes power-of-two color table size matching number of palette colors. More...
static int	BitsForColorTable (int table_size)
	Computes bits of precision needed to index a color table size. More...
static int	GifBitWriter_FlushBlock (GifBitWriter *writer)
	Flushes accumulated byte block buffer of the LZW stream to disk. More...
static int	GifBitWriter_WriteByte (GifBitWriter *writer, u8 value)
	Adds a single byte to the output stream block. More...
static int	GifBitWriter_WriteCode (GifBitWriter *writer, int code, int code_size)
	Writes an LZW code of variable bit length. More...
static int	GifBitWriter_Finish (GifBitWriter *writer)
	Flushes remaining bits and terminates image block. More...
static int	WriteLzwLiteralImageData (FILE *f, const u8 *frame, int width, int height, int scale, int min_code_size)
	Emits LZW literal code stream from pixel index frame data. More...
int	Gif_WriteIndexed (const char *path, const u8 *frames, int frame_count, int width, int height, const RgbaColor *palette, int palette_count, int transparent_index, int delay_cs, int loop_count, int scale)
	Encodes and writes a sequence of indexed frames to a GIF file. More...

Detailed Description

Implementations of custom LZW animated GIF writing utilities.

Macro Definition Documentation

GIF_COMPAT_MIN_FAST_DELAY_CS

#define GIF_COMPAT_MIN_FAST_DELAY_CS   5

Typedef Documentation

GifBitWriter

typedef struct GifBitWriter GifBitWriter

Function Documentation

BitsForColorTable()

static int BitsForColorTable ( int  table_size )

static

Computes bits of precision needed to index a color table size.

Parameters

table_size

Color table size.

Returns

Number of bits.

ColorTableSize()

static int ColorTableSize ( int  color_count )

static

Computes power-of-two color table size matching number of palette colors.

Parameters

color_count

Quantity of colors.

Returns

Resolved size of color table.

Gif_WriteIndexed()

int Gif_WriteIndexed	(	const char *	path,
		const u8 *	frames,
		int	frame_count,
		int	width,
		int	height,
		const RgbaColor *	palette,
		int	palette_count,
		int	transparent_index,
		int	delay_cs,
		int	loop_count,
		int	scale
	)

Encodes and writes a sequence of indexed frames to a GIF file.

Parameters

path	Path to write the final GIF file.
frames	Pointer to 8-bit indexed frame pixel buffer. Size: (width * height * frame_count).
frame_count	Total number of frames in sequence.
width	Canvas width in pixels.
height	Canvas height in pixels.
palette	Pointer to an array of colors defining the color map (palette).
palette_count	Total number of entries in color palette (up to 256).
transparent_index	Index in the palette mapping transparency, or -1.
delay_cs	Base duration between frames in centiseconds (1/100ths of a second).
loop_count	Number of loops (0 = infinite).
scale	Bilinear scale multiplier applied to output image sizes.

Returns

0 on success; negative value on file or encoding failure.

GifBitWriter_Finish()

static int GifBitWriter_Finish ( GifBitWriter *  writer )

static

Flushes remaining bits and terminates image block.

Parameters

writer

Bit writer context.

Returns

0 on success; negative on failure.

GifBitWriter_FlushBlock()

static int GifBitWriter_FlushBlock ( GifBitWriter *  writer )

static

Flushes accumulated byte block buffer of the LZW stream to disk.

Parameters

writer

Bit writer context.

Returns

0 on success; negative on failure.

GifBitWriter_WriteByte()

static int GifBitWriter_WriteByte ( GifBitWriter *  writer, u8  value  )

static

Adds a single byte to the output stream block.

Parameters

writer	Bit writer context.
value	Byte value.

Returns

0 on success; negative on write failure.

GifBitWriter_WriteCode()

static int GifBitWriter_WriteCode ( GifBitWriter *  writer, int  code, int  code_size  )

static

Writes an LZW code of variable bit length.

Parameters

writer	Bit writer context.
code	LZW code value.
code_size	Bit size of the code.

Returns

0 on success; negative on failure.

ResolveCompatibleTiming()

static void ResolveCompatibleTiming ( int  requested_delay_cs, int *  out_frame_step, int *  out_delay_cs  )

static

Resolves compatible delay timing constraints to prevent browser lag.

Parameters

requested_delay_cs	Target requested delay duration.
out_frame_step	Pointer to resolved frame step multiplier.
out_delay_cs	Pointer to output resolved delay duration.

WriteLzwLiteralImageData()

static int WriteLzwLiteralImageData ( FILE *  f, const u8 *  frame, int  width, int  height, int  scale, int  min_code_size  )

static

Emits LZW literal code stream from pixel index frame data.

Parameters

f	Output file stream.
frame	Source indexed pixel frame.
width	Source frame width.
height	Source frame height.
scale	Scaling factor.
min_code_size	Minimum LZW code size.

Returns

0 on success; negative on failure.

WriteU16()

static void WriteU16 ( FILE *  f, int  value  )

static

Writes a 16-bit unsigned integer in little-endian format to a file stream.

Parameters

f	Target file stream.
value	Integer value to write.