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SWF Gradient Record (swf_gradient_record)

SWF Structure Info
Tag Flash Version: 
3
SWF Structure: 
struct swf_gradient_record {
	if(f_tag == DefineMorphShape || f_tag == DefineMorphShape2) {
		unsigned char	f_position;
		swf_rgba	f_rgba;
		unsigned char	f_position_morph;
		swf_rgba	f_rgba_morph;
	}
	else if(f_tag == DefineShape3 || f_tag == DefineShape4) {
		unsigned char	f_position;
		swf_rgba	f_rgba;
	}
	else {
		unsigned char	f_position;
		swf_rgb		f_rgb;
	}
};

The first record position should be 0 and the last 255. The intermediate should use the corresponding value depending on their position in the gradient effect.

SyncFrame

Tag Info
Tag Number: 
29
Tag Type: 
Display
Tag Flash Version: 
3
Brief Description: 

Tag used to synchronize the animation with the hardware.

Tag Structure: 

Unknown

Apparently, Macromedia thought that synchronizing their animation with, probably, the VLB would be a good idea. Yet they dropped it and never released that out. It is probably not useful for animations (visual) to be properly synchronize when there is not audio. If you do have audio, you should synchronize the animation to the audio and drop visual frames as required to keep up with the audio.

SoundStreamHead

Tag Info
Tag Number: 
18
Tag Type: 
Define
Tag Flash Version: 
2
Brief Description: 

Declare a sound effect which will be interleaved with a movie data so as to be loaded over a network connection while being played.

Tag Structure: 
struct swf_soundstreamhead {
	swf_tag			f_tag;		/* 18 or 45 */
	unsigned		f_compression : 4;
	unsigned		f_sound_rate : 2;
	unsigned		f_sound_size : 1;
	unsigned		f_sound_stereo : 1;
	unsigned		f_reserved : 4;
	unsigned		f_playback_rate : 2;
	unsigned		f_playback_size : 1;
	unsigned		f_playback_stereo : 1;
	unsigned short		f_sample_size;
	if(f_compression == 2) {
		signed short	f_latency_seek;
	}
};

The SoundStreamHead[2] tags define a sound effect which is to be loaded with a set of SoundStreamBlock tags. It defines the sound once and for all.

Streaming sound has a strong side effect when playing a movie: it will force a synchronization between the images and the audio. Thus some images may be dropped if the drawing isn't fast enough.

[un]signed long fixed

Tag Flash Version: 
1
Used by PushData Action: 
Not available in PushData Action

A short fixed value1 is a 32 bit (or less) number representing a value with 16 bits on the left of the decimal point and 16 bits on the right.

When the value is smaller than 32 bits, we assume that only the least significant bits were defined (quite often only those after the decimal point.)

For more information about bit fields, check out the [un]signed type.

  • 1. The fixed long type exists since version 1, although it was properly named as such only in version 8 of Flash.

[un]signed short fixed

Tag Flash Version: 
1
Used by PushData Action: 
Not available in PushData Action

A short fixed value1 is a 16 bit (or less) number representing a value with 8 bits on the left of the decimal point and 8 bits on the right.

When the value is smaller than 16 bits, we assume that only the least significant bits were defined (quite often only those after the decimal point.)

For more information about bit fields, check out the [un]signed type.

  • 1. The fixed short type exists since version 1, although it was properly named as such only in version 8 of Flash.

DefineSound

Tag Info
Tag Number: 
14
Tag Type: 
Define
Tag Flash Version: 
2
Brief Description: 

Declare a sound effect. This tag defines sound samples that can later be played back using either a StartSound or a DefineButtonSound. Note that the same DefineSound block can actually include multiple sound files and only part of the entire sound can be played back as required.

Tag Structure: 
struct swf_definesound {
	swf_tag			f_tag;		/* 14 */
	unsigned short		f_sound_id;
	unsigned		f_sound_format : 4;
	unsigned		f_sound_rate : 2;
	unsigned		f_sound_is_16bits : 1;
	unsigned		f_sound_is_stereo : 1;
	unsigned long		f_sound_samples_count;
	unsigned char		f_sound_data[<variable size>];
};

A DefineSound tag declares a set of samples of a sound effect or a music.

The sound samples can be compressed or not, stereo or not and 8 or 16 bits. The different modes are not all available in version 2, although the same tag is used in newer versions with additional capabilities.

The f_sound_is_16bits is always set to 1 (16bits samples) if the samples are compressed (neither Raw nor Uncompressed).

DefineFont

Tag Info
Tag Number: 
10
Tag Type: 
Define
Tag Flash Version: 
1
Brief Description: 

List shapes corresponding to glyphs.

Tag Structure: 
struct swf_definefont {
	swf_tag			f_tag;		/* 10 */
	unsigned short		f_font_id;
	/* there is always at least one glyph */
	f_font_glyphs_count = f_font_offsets[0] / 2;
	unsigned short		f_font_offsets[f_font_glyphs_count];
	swf_shape		f_font_shapes[f_font_glyphs_count];
};

It is common to use the DefineFont tag in order to create an array of shapes later re-used to draw strings of text on the screen. Note that the definition of the shape within a font is limited since it can't include any specific fill and/or line style. Also, each shape is assumed to be defined within a 1024x1024 square. This square is called the EM Square. Fig 1. below shows you the EM Square and how it is used. The characters baseline can be placed anywhere within the EM Square (it certainly can be outside too if you wish?!?).

DefineBitsJPEG

Tag Info
Tag Number: 
6
Tag Type: 
Define
Tag Flash Version: 
1
Brief Description: 

Define a JPEG bit stream.

Tag Structure: 
struct swf_definebitsjpeg {
	swf_long_tag		f_tag;		/* 6, 21, 35 or 90 */
	unsigned short		f_image_id;
	if(f_tag == DefineBitsJPEG3 + f_tag == DefineBitsJPEG4) {
		/* sizeof(f_encoding_tables) + sizeof(f_image_data) + 2 when JPEG4 */
		unsigned long		f_offset_to_alpha;
	}
	if(f_tag == DefineBitsJPEG4) {
		unsigned short fixed	f_deblocking_filter_parameter;
	}
	if(f_tag != DefineBitsJPEG) {
		/* when DefineBitsJPEG, use JPEGTables instead */
		unsigned char		f_encoding_tables[<variable size>];
	}
	unsigned char		f_image_data[<variable size>];
	if(f_tag == DefineBitsJPEG3 || f_tag == DefineBitsJPEG41) {
		unsigned char		f_alpha[<variable size>];
	}
};
  • 1. JPEG4 optionally accepts the f_alpha field. [To be verified]

These tags define an image saved using the JPEG compression scheme.

DefineBitsJPEG (V1.0) does not include the encoding tables which are defined in the unique JPEGTables tag instead. All the DefineBitsJPEG of an SWF file use the only JPEGTables tag. Yes... This means you need a tool that is capable of reusing the same tables over and over again to make sure that all your DefineBitsJPEGs work properly (or use it just once.)

The other tags incorporate their own version of the JPEG encoding tables.

The DefineBitsJPEG3 and DefineBitsJPEG4 support an alpha channel bit plane (8 bits.) ...

PlaceObject

Tag Info
Tag Number: 
4
Tag Type: 
Display
Tag Flash Version: 
1
Brief Description: 

Place the specified object in the current display list.

Tag Structure: 
struct swf_placeobject {
	swf_tag			f_tag;		/* 4 */
	unsigned short		f_objec_id_ref;
	unsigned short		f_depth;
	swf_matrix		f_matrix;
	if(f_tag_data_real_size is large enough) {1
		swf_color_transform	f_color_transform;
	}
};
  • 1. The f_color_transform is an optional field. The size of the tag data determines whether it was saved or not.

This tag will be used to specify where and how to place an object in the next frame. The PlaceObject2 and PlaceObject3 tags are much different and is presented below.

About SWF

Brief History

At the very beginning, a company created the SWF format to generate small vector animations on the Internet called Shockwave Flash (hence the name of the format, SWF.) It also included images. This company was bought by Macromedia around 1997 (if I recall properly). This is when Flash v3 was created. Since then, Macromedia created a new version about once a year up to version 8. At that time (in 2005/2006), Macromedia sealed a deal with Adobe which wanted to use the SWF format in their PDF files.

Today (May 1st, 2008), the SWF format is available for free to all. It can be ...