Basic Data Types

This section describes the basic data types used to define the more complex data structures that comprise the SWF file format.

Bit Values

Bit values are a linear sequences of bits that describe signed and unsigned integer and fixed point values. Other types of values that follow one or more bit values are always aligned to the nearest byte boundary with zero bits as padding.

Integer Values

Integer values are 8-bit, 16-bit, and 32-bit signed and unsigned values.

Fixed-Point Values

Fixed values are a 32-bit signed fixed-point number (16.16).

Color Values

A color value represents a 24-bit red, green, and blue value.

The format for a color value within the file is described in the following table:

ColorWithAlpha Values

A ColorWithAlpha value represents a 32-bit red, green, and blue value with transparency information.

The format for a color value within the file is described in the following table:

Rectangle Values

A rectangle value represents a rectangular region defined by a minimum X- and Y-coordinate position with a maximum X- and Y-coordinate position.

The format for a rectangular value within the file is described in the following table:

Matrix Values

Color Transform Values

** The order of the bits HasMultTerms and HasAddTerms reversed. (PH 99.04.01). Confirmed (DM 99.07.07)

Color Transform with Alpha Values

** The order of the bits HasMultTerms and HasAddTerms reversed. (PH 99.04.01). Confirmed (DM 99.07.07)

String Values

A string value represents a null terminated ASCII or multiple byte character string.

The format for a string value is a sequential list of bytes terminated by the null character byte.

SWF File Tags

There are two categories of tags: definition and control. Definition tags manage a dictionary of resources such as shapes, text, bitmap, and buttons that can be used at any point in the animation. Control tags control the display list and enable actions such as stopping or starting the animation.

The following lists show the tags by category.

Definition tags

Control tags

Definition Tags

You use definition tags to create animation characters such as shapes, text, bitmap, and buttons. The following sections describe the data types and tags associated with each character type.

The following lists show the tags associated with each character.

Shapes

Bitmaps

Buttons

Text/Font

Sound

Sprite

DefineSprite

Shape Architecture

Shapes in a SWF file have a flexible and powerful data structure that can be very efficiently rendered on the display. A shape is defined by the following elements:

• Fill styles—A shape begins with a list of all the fill styles used in a shape.
• Line styles—This is followed by a list of all the line styles used in a shape.
• Edges—Finally, there is a list of the Bezier curve edges that define the shape.

In most PC vector graphics formats, shapes are defined by a path data structure that has fill and line styles and a series of curves or lines. SWF extends this format by allowing each curve in a shape to have

• Any style from a list line styles
• A boundary between 0, 1, or 2 different filled areas.

This flexible data structure is, in part, what enables SWF vectors to be small and rendered quickly. Note that filled shapes in a SWF file always use the even-odd fill rule.

Fill Types

SWF supports three basic types of fills for a shape.

• Solid fill—A simple RGBA color that fills a portion of a shape.
• Gradient Fill —A gradient fill can be either a linear or a radial gradient. The gradient model has a color ramp that is mapped on to a square of -16384, -16384, 16384, 16384. For a linear gradient, the first color is mapped to the left edge and the last color is mapped to the right edge. For a radial gradient, the first color is mapped to the center point of the gradient and the last color is mapped to the largest circle that fits inside the gradient square. These color spaces are mapped on to the display using a standard transformation matrix. The color ramps consist of up to eight RGBA colors, where each color has a ratio between 0 and 255 that determines where in the ramp the color is located. Colors must be sorted with the smallest ratio first.
• Bitmap fill—Bitmap fills refer to a bitmap character. There are two styles: clipped and tiled. A clipped bitmap fill repeats the color on the edge of a bitmap if the fill extends beyond the edge of the bitmap. A tiled fill repeats the bitmap if the fill extends beyond the edge of the bitmap.

A fill style array enumerates a number of fill styles.

The format of a fill style array is described in the following table:

A fill style represents how a close shape is filled in.

The format of a fill style value within the file is described in the following table:

** For defining clipped bitmap filled shapes, 2 fillstyles are used:
The first one has a FillStyleType of 0x41, a bitmap id of 65535, and a matrix that defines the mapping of pixels on to the geomety.
The second fillstyle has a FillStyleType of 0x41, the bitmap id of the image to use, and a matrix that is applied to the outline geometry.
The first Fillstyle can be eliminated. It appears to be a bug in the authoring tool. (PH 99.01.05)

Gradient Values

Gradient information for a fill style.

The format of gradient information is described in the following table:

The gradient record format is:

Line Style Values

A line style array enumerates a number of line styles.

The format of a line style array is described in the following table:

A line style represents a width and color of a line.

The format of a line style value within the file is described in the following table:

Shape Values

Shape values define an open or closed shape without a fill style or line style record.

The format of shape style information is described in the following table:

A shape style record is the same as a shape except that a fill style and line style array is appended to the beginning of the data. These records are used in shape characters.

The format of shape style information is described in the following table:

There are three types of shape records.

Shape Record Type 0 defines the end of shape record.

Shape Record Type 1 defines changes in line style, fill style, position or a new set of styles.

Shape Record Type 2 defines a straight or curved edge

Edge Records

There are two types of edge records.

Edge Record Type 0 - defines a curved edge

Edge Record Type 1 - defines a straight edge

DefineShape

Defines a vector shape object. The shape definition is a run-length encoded list of bezier curve information, line styles, and fill styles. A shape can contain many different fill colors and line styles. This format compresses very well since each curve segment has its own fill and line attributes.

A mathematical gradient fill ability and the ability to fill an area with a bitmap enables rich graphics.(SWF 1.0)

DefineShape2

Extends the capabilities of DefineShape with the ability to support more than 255 styles in the style list and multiple style lists in a single shape. (SWF 2.0)

DefineShape3

Extends the capabilities of DefineShape2 by extending all of the RGB color fields to support RGBA with alpha transparency. (SWF 3.0)

DefineMorphShape

A morph fill style array enumerates a number of fill styles.

The format of a fill style array is described in the following table:

A fill style represents how a close shape is filled in.

The format of a fill style value within the file is described in the following table:

Morph Gradient Values

Gradient information for a fill style.

The format of gradient information is described in the following table:

The gradient record format is:

Morph Line Style Values

A morph line style array enumerates a number of fill styles.

The format of a line style array is described in the following table:

A line style represents a width and color of a line. DefineMorphShape supports only solid line styles.

The format of a line style value within the file is described in the following table:

Bitmaps

SWF supports a variety of bitmap formats. One JPEG format has a JPEG header that is shared between multiple JPEG images in a single SWF file to minimize file size. Another JPEG format lets each image have it's own header, allowing each image its own compression settings. The zlib format is similar to an embedded PNG file and is used when you need lossless image compression. This is best for images that would compress well as a GIF file like screen shots or diagrams while JPEG is best for photographs.

Bitmaps in SWF can also contain alpha channel information. For lossless compression, there can be alpha channel information in a color table of an 8-bit image or there can be full alpha channel information for a 32-bit image. For JPEG images, alpha channels are stored using lossless zlib compression.

Note that when a bitmap in a SWF file is rendered, the full transform operation is applied to the image including the matrix transformation and the color transform operation.

DefineBits

Defines a bitmap character with JPEG compression. This tag contains only the JPEG compressed image data (as defined by the Independent JPEG Group). JPEGTables contains the JPEG encoding data used to encode this image. (SWF 1.0)

DefineBitsJPEG2

Defines a bitmap character with JPEG compression. This tag differs from DefineBits in that the record contains both the JPEG encoding table and the JPEG image data (as defined by the Independent JPEG Group). This record allows multiple JPEG images with differing compression ratios to be defined within a single SWF file.

Note: The JPEG encoding data and image data contained within this record are in two separate JPEG streams. Each JPEG stream has a beginning of stream tag (0xFF, 0xD8) and an end of stream tag (0xFF, 0xD9). This differs from a standard JPEG image which combines the encoding data and image data into a single stream. (SWF 2.0)

DefineBitsJPEG3

Defines a bitmap character with JPEG compression. This tag differs from DefineBitsJPEG2 because it contains alpha channel data. This record allows multiple JPEG images with differing compression ratios to be defined within a single SWF file.

Note: The JPEG encoding data and image data contained within this record are in two separate JPEG streams. Each JPEG stream has a beginning of stream tag (0xFF, 0xD8) and an end of stream tag (0xFF, 0xD9). This differs from a standard JPEG image which combines the encoding data and image data into a single stream. (SWF 3.0)

DefineBitsLossless

Defines a loss-less bitmap character that contains raw ZLIB compressed image data. The data format used by the ZLIB library is described by Request for Comments (RFCs) documents 1950 to 1952. (SWF 2.0)

DefineBitsLossless2

Defines a loss-less bitmap character that contains raw ZLIB compressed image data and alpha channel information. The data format used by the ZLIB library is described by Request for Comments (RFCs) documents 1950 to 1952. (SWF 3.0)

** Originally read if "bmFormat <= 3 UI8(n-1)", but bmFormat == 0, 1, 2 are undefined?

JPEGTables

Defines the JPEG encoding table (as defined by the Independent JPEG Group) for the JPEG images defined using the DefineBits records. There should only be one record of this type in a SWF file. (SWF 1.0)

Buttons

Button objects provide much of the interactivity in a SWF file. A button object consists of four states. The objects active in the first state are displayed when the button is idle. The objects in the second state are displayed when the mouse is over the button. The objects in the third state are displayed when the button is pressed by the mouse. The objects in the fourth state are used as a hit area to determine when the mouse is over the button. Buttons track the mouse in two ways: by push button and by menu button. Push buttons capture the mouse until the mouse button is released. Menu buttons do no capture the mouse.

Buttons can perform actions based on certain state transitions. The list of possible button state transitions are:

IdleToOverUp—Mouse enter up

OverUpToIdle—Mouse exit up

OverUpToOverDown—Mouse down

OverDownToOverUp— Mouse up in

Push button transitions
These transitions only apply when tracking Push buttons:

OverDownToOutDown—Mouse exit down

OutDownToOverDown—Mouse enter down

OutDownToIdle—Mouse up out

Menu button transitions
These transitions only apply when tracking Menu buttons:

IdleToOverDown—Mouse enter down

OverDownToIdle—Mouse exit down

Typically button actions are performed on a OverDownToOverUp, but they can be performed on any state transition.

DefineButton

Defines a button character. A button is defined by an up image, mouse over image, depressed image and a hit region. There is also a list of actions to take when the button is clicked and released. See the DoAction tag. (SWF 1.0)

Button Records

Button records describe the shape and text characters that comprise a button. Each character in a button must be associated with one or more states (up, down, over or hit test).

Button Record—The state flags below indicate where a given character should be used for that state of the button.

DefineButton2

Defines a button character. A button is defined by an up image, mouse over image, depressed image, and a hit region. You can also specify color transformation and sound data. There is also a list of actions to take when the button is clicked and released. See the DoAction tag. (SWF 3.0)

** After the Flags field there is an Offset (UI16) to end of the Buttons. (PH 99.01.05)

** The ActionOffset preceeding the last Button2ActionCondition should be 0. (PH 99.01.05)

Button Records

Button records describe the shape and text characters that comprise a button. Each character in a button must be associated with one or more states (up, down, over or hit test).

Button Record—The state flags below indicate where a given character should be used for that state of the button.

** There is only one ColorTransform in each button record, originally CXFORM[nCharacters in button]. (PH 99.05.01)

DefineButtonCxform

Defines the color transform for each shape and text character in a button. Not used for DefineButton2. (SWF 2.0)

** There is only one ColorTransform in each button record, originally CXFORM[nCharacters in button]. (PH 99.01.05)

DefineButtonSound

Defines the sound data for a button. (SWF 2.0)

Fonts and Text

SWF defines an efficient font format. The font object defines the outlines of characters in a font. Only the characters that are actually used in the SWF file need to be stored in the font definition. Outlines are stored without any hinting information. (Since SWF graphics are normally anti-aliased, font quality is quite good without any hinting information.) Text objects in a SWF file consist of positioning information for each character to be placed and an index into a font object for the font outline.

The SWF font scheme has several advantages. The font definitions make it easy to reuse outlines, saving file size. These definitions also make it possible to use the font rendering engine of a platform (if that technique has advantages for a particular platform). Since the layout and positioning information is stored in the text object, it is possible to do very sophisticated text layout effects like kerning and text wrapping without having a complex layout engine built into a SWF file format player.

DefineFont

Defines the shape outlines that define each glyph used in a particular font. Only the glyphs that are used in a font are actually defined. This record consists of an offset table followed by a shape table. For each glyph in the shape table. the offset table stores the offset of the glyph in bytes from the start of the offset table. Also, there is a one-to-one ordering match between the order of the glyph offsets in the offset table and the order of the glyph shapes in the shape table. The number of glyphs in the shape table can be inferred by determining the offset of the first glyph shape and dividing the offset by two bytes for each offset entry. (SWF 1.0)

DefineFont2

Defines the mapping from a font object to a device font so that the player can optionally use a TrueType or ATM font that may be installed on the computer instead of the stored glyph outlines. Also defines the shape outlines that define each glyph used in a particular font. This record consists of an offset table followed by a shape table; you have the option of extending the offset table to 32 bits. For each glyph in the shape table the offset table stores the offset of the glyph in bytes from the start of the offset table. Also, there is a one to one ordering match between the order of the glyph offsets in the offset table and the order of the glyph shapes in the shape table. (SWF 3.0)

*If FontFlagsHasLayout has been set, each kerning structure has the following data:

FontKerningCode1. If FontFlagsWideCodes is 1, UI16 else UI8.

FontKerningCode2. If FontFlagsWideCodes is 1, UI16 else UI8.

FontKerningAdjustment. SI16

** In the original SWF reference the FontFlagsReserved field came before the FontFlags, which was not true to the actual file format. (JW 99.04.19)

Comment from PH about DefineFont2:
FontGlyphCount - gives the count of glyphs in the font - nGlyphs.
This is followed by FontOffsetTable[nGlyphs] then SHAPE[nGlyphs].

In a file I was decoding I received the value nGlyphs = 224 , then the first offset value in the FontOffsetTable as 450 ( U16 ) . This implies that the the font offset table is 450 bytes long, and that there are 450 / 2 or 225 glyphs.. I have treated it as if there is 2 bytes of padding at the end of the fontOffsetTable and the SHAPE table. Maybe I am parsing the DefineFont2 tag incorrectly, although I have been through the code countless times and it seems right.

DefineFontInfo

Defines the mapping from a font object to a device font so that the player can optionally use a TrueType or ATM font that may be installed on the computer instead of the stored glyph outlines. This record also contains information that can be used to map glyph indices in a text record to character codes to reconstruct the original string data. (SWF 1.0)

DefineText

Defines a text object. This is a complex record that describes the font, height, color, and position of every text character in the record. (SWF 1.0)

Text records specify either changes to the state of text or actual glyph indices for text.

Text Record Type 0

Text Record Type 1

** The Type for TextRecordType changed to read UB[1]=1 instead of UB[1]=0. (PH 99.04.01)

** The fields TextXOffset and TextYOffset changed to SI16 instead of UI16. (PH 99.04.01)

Glyph entries describe the glyph index and X advance value to use for a particular character in the currently selected font for the text record.

DefineText2

Defines a text object with color transparency data. This is a complex record that describes the font, height, color, and position of every text character in the record. (SWF 3.0)

Text records specify either changes to the state of text or actual glyph indices for text.

Text Record Type 0

Text Record Type 1

Glyph entries describe the glyph index and X advance value to use for a particular character in the currently selected font for the text record.

Sounds

The SWF file format defines a small and efficient sound model. Sounds are stored as 2-, 3-, 4- or 5-bit ADPCM. This simple but efficient compression scheme avoids any licensing or patent issues that arise with more sophisticated sound compression schemes and helps to keep player implementations very small. SWF supports sample rates of 5.5, 11, 22 and 44 khz in both stereo and mono. It is assumed that the playback platform can support rate conversion and multi-channel mixing of these sounds.

The number of simultaneous channels supported depends on the CPU of specific platforms, but is typically three to eight channels. There is also the concept of a sound envelope where a simple transform can be applied to a sound object to generate various types of fades and level control (fade-in, fade-out, cross-fade).

Sounds in SWF are stored as individual sound objects that can be reused and mixed at runtime. The SWF file format also supports a streaming sound mode where sound data is played and downloaded in tight synchronization with the timeline. In this mode, sound packets are stored with each frame. If a CPU cannot render the frames of a movie as quickly as specified by the frame rate of the movie, the player slows down the animation rate instead of skipping frames. When streaming sound is present, the player skips frames in order to maintain tight synchronization with the sound track.

Note that a timeline can only have a single streaming sound playing at a time, but each movie clip can have it's own streaming sound.

See Also: StartSound

Sound Information Values

Sound information modifies how a sound character is played.

The format of sound information is described in the following table:

** The 4 SyncFlags bits moved to before the the HasEnvelope bits, instead of after the HasInPoint bit. (PH 99.04.01)

The sound envelope record format is

DefineSound

Defines the data for a sound. (SWF 2.0)

SoundStreamBlock

Defines sound data that is interleaved with frame data so that sounds can be played as the movie is streamed over a network connection. (SWF 2.0)

SoundStreamHead

Defines the start of sound data that is interleaved with frame data so that sounds can be played as the movie is streamed over a network connection. Does not support uncompressed sound. (SWF 2.0)

SoundStreamHead2

Defines the start of sound data that is interleaved with frame data so that sounds can be played as the movie is streamed over a network connection. Supports uncompressed sound. (SWF 3.0)

Sprites

SWF sprites (movie clips) are a SWF movie contained within a SWF movie. A sprite tag consists of a series of control tags. All the definition tags should be defined in the main body of the file before the sprite is defined. When a sprite is placed on the display list, it starts a new thread of control where the frames of the sprite are processed independently of the current main timeline frame. A sprite is stopped when it is removed from the display list. The objects placed by a sprite are added to the display list as children of the sprite object. The sprite transform is concatenated to the object transforms.

DefineSprite

Defines a sprite. (SWF 3.0). Sprites are a grouped series of tags. They allow you to nest tags. Each sprite has an independent timeline.

** The frame count (UI16) between SpriteID and <mini file structure> was missing in the original spec (MS 99.07.12)

The valid tags within a sprite are as follows:

ShowFrame

PlaceObject

PlaceObject2

RemoveObject

RemoveObject2

DoAction

StartSound

FrameLabel

SoundStreamHead

SoundStreamBlock

End

Control Tags

Control tags can be divided into three categories: display list, control, and action. The following sections describe each category and its tags.

Display List tags

Control tags

Action tags

DoAction

Display List

Display list tags control the contents of the display list. (See the Display List section for more information on the display list.) The following tags are display list:

PlaceObject and PlaceObject2—Place the specified object on the display list.

RemoveObject and RemoveObject2—Remove the specified object from the display list.

ShowFrame—Displays the display list contents on screen.

PlaceObject

Places the indicated character on the display surface with an arbitrary PostScript style transformation matrix. Also includes a depth parameter to indicate a stacking order. Each character can be placed many times on the screen. If the length of the record indicates a size that exceeds the end of the transformation matrix, it is assumed that color transformation data is appended to the record. (SWF 1.0)

PlaceObject2

Places the indicated character on the display surface with an arbitrary PostScript style transformation matrix. Also includes a depth parameter to indicate a stacking order. Each character can be placed many times on the screen. (SWF 3.0)

RemoveObject

Removes the indicated character from the display surface. (SWF 1.0)

RemoveObject2

Removes the character from the display surface. (SWF 3.0)

ShowFrame

Flags the end of the current frame. During playback, the characters present in the display list (see PlaceObject/RemoveObject) should be rendered and movie paused for the duration of a single frame. (SWF 1.0)

Control

Control tags manage some overall aspects of files and frames. The following tags are control tags:

SetBackgroundColor—Sets the background color displayed in the frame.

FrameLabel—Labels a frame for your easy reference.

Protect—Marks the file so that it cannot be opened in the authoring system.

StartSound—Starts and stops a sound.

End—Marks the end of the SWF file.

SetBackgroundColor

Set the background color of the display. (SWF 1.0)

FrameLabel

Names a frame. (SWF 3.0)

Protect

Marks a file as not importable for editing in the authoring tool. If this tag is present in the file, the authoring tool should prevent loading of the file for editing. (SWF 2.0)

StartSound

Starts playing a sound character. You can stop a sound by setting the synchStop flag in the SoundInfo structure used by DefineSound. (SWF 2.0)

End

Marks the end of a file. This should always be the last tag in a file. (SWF 1.0)

Actions

The SWF File format defines a simple action model. An action list can be attached to a button state transition or placed in the tags that will be processed for a given frame. There are 127 possible actions of which 13 are currently defined. An action list consists of an 1-byte action code. If the high bit of the action code is set, then there is a 16 bit length that describes the amount of data used by the action. If the high bit is clear, the action has no data.

When an action is encountered, it is added to a list to be processed. The list is processed on a ShowFrame tag or after a button state has changed. An action can cause other actions to be triggered, in which case, the action is added to the list of actions to be processed. Actions are processed until the action list is empty.

Actions such as stop, play and go to frame apply to a particular timeline. By default, they apply to the timeline which contains them. However, the SetTarget action (tell target) can be used to send an action to another timeline.

Action Values

Action values specify an action the player should perform when the frame is complete, when a button is pressed, or when a do action tag is encountered.

Action Goto Frame—Go to the specified frame.

Action Get URL—Direct the player to get the specified URL.

** The special significance of the targets _level1, _level0 should be described.
Also the effect of giving a zero length URL and a target of _level1 should be documented. (PH 99.01.10)

Action Next Frame—Go to the next frame.

Action Previous Frame—Go to the previous frame.

Action Play—Start playing at the current frame.

Action Stop—Stop playing the movie at the current frame.

Action Toggle Quality—Toggle the display between high and low quality.

Action Stop Sounds—Stop playing all sounds.

Action Wait For Frame—Wait until the specified frame otherwise skip the specified number of actions.

Action Set Target—Sets context of action.

Action Go to Label—Go to frame associated with the specified label.

DoAction

Flags that the specified actions should be performed when the frame is complete. (SWF 1.0)