.SWF File Format – Shapes

The shape tags

DefineShape (2)

Colours are RGB. Each style list has at most 255 entries, and the records cannot start new style lists.

DefineShape2 (22, SWF 2)

The same fields as DefineShape. A style count of 0xFF is followed by a UI16 with the real count, and a style change record may carry new style lists (StateNewStyles). Colours are RGB.

DefineShape3 (32, SWF 3)

The same fields as DefineShape2, with RGBA colours in every fill style, gradient record and line style.

DefineShape4 (83, SWF 8)

SHAPEWITHSTYLE

SHAPE

A shape without style lists, used for font glyphs and for the edges of morph shapes: UB[4] NumFillBits, UB[4] NumLineBits, then SHAPERECORD[] to the end record. A glyph uses fill style 1, which is implied, and no lines.

Fill styles

A FILLSTYLEARRAY is a UI8 FillStyleCount; if it is 0xFF (DefineShape2 and later), a UI16 FillStyleCountExtended follows with the real count. Then the FILLSTYLEs. Records refer to them by index from 1; 0 means no fill.

0x42 and 0x43 came later than 0x40 and 0x41; the version is not confirmed here. The bitmap matrix maps bitmap pixels into the shape’s twips, so a scale of 20 draws one bitmap pixel to one screen pixel.

Gradients

A gradient is drawn in a square of its own that runs from −16,384 to 16,384 twips (819.2 pixels) each way; the gradient matrix maps that square onto the shape. A linear gradient sets the colour by x, ratio 0 at the left edge and 255 at the right. A radial gradient sets it by distance from the centre, 255 at a radius of 16,384.

Line styles

A LINESTYLEARRAY is a UI8 LineStyleCount, 0xFF then a UI16 for more in DefineShape2 and later, then LINESTYLEs (DefineShape to DefineShape3) or LINESTYLE2s (DefineShape4). Index 0 in a record means no line.

LINESTYLE: UI16 Width in twips, then an RGB colour (DefineShape, DefineShape2) or RGBA (DefineShape3).

LINESTYLE2 (SWF 8):

Shape records

The records are packed into bits one after another, with no padding between them; the run is padded to a byte after its end record. The pen starts at (0, 0). The first bit says which kind of record follows: 0 a style change or the end, 1 an edge.

Fills on two sides

Every edge carries the current FillStyle0 and FillStyle1: the fill on each side of it as it is drawn, FillStyle0 on the left and FillStyle1 on the right in the specification’s terms. Flash draws shapes this way so that touching regions share one edge. To fill a shape:

1. Walk the records, keeping the pen and the current styles, and turn each edge into a segment with its two fill styles and its line style.
2. For each fill style, take the edges that have it as FillStyle1 as they were drawn, and the edges that have it as FillStyle0 reversed.
3. Join them end to end into closed outlines, all wound the same way, and fill those. The explorer uses the non-zero rule.
4. Draw the lines over the fills, edge by edge, in each edge’s line style.

A worked example

A DefineShape2 from a SWF 6 movie: a grey circle 2 pixels wide with a red outline, 54 bytes.

00000065  BF 05 30 00 00 00 04 00 35 8A 58 A0 01 00 D3 D3
00000075  D3 01 01 00 FF 00 00 11 2C CA 01 C6 04 68 D1 E8
00000085  D8 04 78 06 B5 1E B4 0C 46 0C 1B 51 9B 48 04 68
00000095  01 8D 19 8C 04 00

• BF 05 is 0x05BF: code 22, DefineShape2, length 63, so the long form; 30 00 00 00 is 48 bytes. 04 00 is shape 4.
• RECT 35 8A 58 A0: Nbits 6, then −20, 20, −20, 20 twips: −1 to 1 pixel each way.
• Fill styles: 01, one; 00 D3 D3 D3, solid #D3D3D3. Line styles: 01, one; 01 00, 1 twip wide, FF 00 00 red.
• 11: NumFillBits 1, NumLineBits 1.
• 2C CA 01 C6 begins the records: 0 a style change; 0 1 0 1 1: no new styles, a line style, no FillStyle1, a FillStyle0, a move. MoveBits 00110 is 6; MoveDeltaX 010100 is 20, MoveDeltaY 000000 is 0; FillStyle0 1; LineStyle 1.
• Eight curved edges follow, each 1 0 then NumBits 0011 (5-bit deltas). The first has control (0, 8) and anchor (−6, 6): from (20, 0) through (20, 8) to (14, 14), an eighth of the circle.
• The end record’s six zero bits and the padding finish the last bytes.

DefineMorphShape (46, SWF 3)

Every morph style holds a start and an end value of each of its parts. A morph fill is a UI8 type, then for a solid fill RGBA StartColor and RGBA EndColor; for a gradient a start and an end MATRIX and a morph gradient; for a bitmap a UI16 BitmapId and a start and an end MATRIX. A morph gradient is a plain UI8 NumGradients, with no spread or interpolation bits, then each record as UI8 StartRatio, RGBA StartColor, UI8 EndRatio, RGBA EndColor. A morph line is UI16 StartWidth, UI16 EndWidth, RGBA StartColor, RGBA EndColor. The array counts work as in shapes: a UI8, or 0xFF and a UI16.

EndEdges has the same edges as StartEdges, edge for edge, with no style changes of its own. The player draws the shape at the PlaceObject2 ratio: each coordinate, colour, width and matrix entry is start + (end − start) × ratio ÷ 65,535.

Flash 5 wrote empty morph shapes with Offset 0; the start edges then end at their end record.

DefineMorphShape2 (84, SWF 8)

DefineMorphShape with four more fields after EndBounds, and MORPHLINESTYLE2 line styles:

A MORPHLINESTYLE2 is UI16 StartWidth and UI16 EndWidth, then the same cap, join and flag bits as LINESTYLE2, the miter limit when the join is a miter, then RGBA StartColor and EndColor, or a morph fill style when HasFillFlag is set.