Chapter 4: The_Display_List

The Display List

• Displaying a frame of a SWF file is a three-stage process:
• 1. Objects are defined with definition tags such as DefineShape, DefineSprite, and so on. Each object is given a unique ID called a character, and is stored in a repository called the dictionary.
• 2. Selected characters are copied from the dictionary and placed on the display list, which is the list of the characters that will be displayed in the next frame.
• 3. Once complete, the contents of the display list are rendered to the screen with ShowFrame.

...

Clipping layers

Using the display list

Display list tags

PlaceObject

• The PlaceObject tag adds a character to the display list.
• The CharacterId identifies the character to be added.
• The Depth field specifies the stacking order of the character.
• The Matrix field species the position, scale, and rotation of the character.
• If the size of the PlaceObject tag exceeds the end of the transformation matrix, it is assumed that a ColorTransform field is appended to the record.
• The ColorTransform field specifies a color effect (such as transparency) that is applied to the character. The same character can be added more than once to the display list with a different depth and transformation matrix.

• NOTE (これ、何処からコピーした？)
  • If a character does not change from frame to frame, you do not need to replace the unchanged character after each frame.
• NOTE
  • PlaceObject is rarely used in SWF 3 and later versions; it is superseded by PlaceObject2 and PlaceObject3.
• The minimum file format version is SWF 1.

• PlaceObject

  Field	Type	Comment
  Header	RECORDHEADER	Tag type = 4
  CharacterId	UI16	ID of character to place
  Depth	UI16	Depth of character
  Matrix	MATRIX	Transform matrix data
  ColorTransform (optional)	CXFORM	Color transform data

PlaceObject2

• The PlaceObject2 tag extends the functionality of the PlaceObject tag.
• The PlaceObject2 tag can both add a character to the display list, and modify the attributes of a character that is already on the display list.
• The PlaceObject2 tag changed slightly from SWF 4 to SWF 5.
• In SWF 5, clip actions were added.

• The tag begins with a group of flags that indicate which fields are present in the tag.
• The optional fields are CharacterId, Matrix, ColorTransform, Ratio, ClipDepth, Name, and ClipActions.
• The Depth field is the only field that is always required.
• The depth value determines the stacking order of the character.
• Characters with lower depth values are displayed underneath characters with higher depth values.
• A depth value of 1 means the character is displayed at the bottom of the stack.
• Any given depth can have only one character.
• This means a character that is already on the display list can be identified by its depth alone (that is, a CharacterId is not required).
• The PlaceFlagMove and PlaceFlagHasCharacter tags indicate whether a new character is being added to the display list, or a character already on the display list is being modified.
• The meaning of the flags is as follows:

  ■ PlaceFlagMove = 0 and PlaceFlagHasCharacter = 1

• A new character (with ID of CharacterId) is placed on the display list at the specified depth.
• Other fields set the attributes of this new character.

  ■ PlaceFlagMove = 1 and PlaceFlagHasCharacter = 0

• The character at the specified depth is modified.
• Other fields modify the attributes of this character.
• Because any given depth can have only one character, no CharacterId is required.

  ■ PlaceFlagMove = 1 and PlaceFlagHasCharacter = 1

• The character at the specified Depth is removed, and a new character (with ID of CharacterId) is placed at that depth.
• Other fields set the attributes of this new character.
• For example, a character that is moved over a series of frames has PlaceFlagHasCharacter set in the first frame, and PlaceFlagMove set in subsequent frames.
• The first frame places the new character at the desired depth, and sets the initial transformation matrix.
• Subsequent frames replace the transformation matrix of the character at the desired depth.
• The optional fields in PlaceObject2 have the following meaning:
• ■ The CharacterId field specifies the character to be added to the display list.
  • CharacterId is used only when a new character is being added.
  • If a character that is already on the display list is being modified, the CharacterId field is absent.
• ■ The Matrix field specifies the position, scale and rotation of the character being added or modified.
• ■ The ColorTransform field specifies the color effect applied to the character being added or modified.
• ■ The Ratio field specifies a morph ratio for the character being added or modified.
  • This field applies only to characters defined with DefineMorphShape, and controls how far the morph has progressed.
  • A ratio of zero displays the character at the start of the morph.
  • A ratio of 65535 displays the character at the end of the morph.
  • For values between zero and 65535 Flash Player interpolates between the start and end shapes, and displays an inbetween shape.
• ■ The ClipDepth field specifies the top-most depth that will be masked by the character being added.
  • A ClipDepth of zero indicates that this is not a clipping character.
• ■ The Name field specifies a name for the character being added or modified.
  • This field is typically used with sprite characters, and is used to identify the sprite for SetTarget actions.
  • It allows the main file (or other sprites) to perform actions inside the sprite (see “Sprites and Movie Clips” on page 231). ■ The ClipActions field, which is valid only for placing sprite characters, defines one or more event handlers to be invoked when certain events occur.

• The minimum file format version is SWF 3.

  (以下、フィールド詳細)

PlaceObject3

ClipEventFlags

RemoveObject

RemoveObject2

ShowFrame