OakPDT Drawing

File Format
Name	OakPDT Drawing
Ontology	Electronic File Formats 3D and CAD/CAM Models OakPDT Drawing

Overview

OakPDT is a 2D parametric CAD system for RISC OS. On RISC OS systems, files in this format typically have a filetype of CAD ("PDT Dwg").

Format details

File Header
0	Byte	Major version number of the file format (always 1)
1	Byte	Minor version number of the format 2 corresponds to OakPDT v2.50 (17 November 1990)
2	Null-terminated string	The_Design_System or Oak_P_D_T_Drawing
20	Integer	Number of symbols (s)
24	Array	s symbol table entries
	Integer	Size of drawing definition (v)
	Array	v bytes
	Byte	Paper size
	Struct	Window definition
	Struct	Grid information
	Struct	Text information
	Struct	Dimension information
	Struct	Line style information
	Integer	Number of scalars (n)
	Array	n scalar table entries
	Struct	Error information
	Struct	Layer information
	Double	Dimension scale (only in v1.1 or later)
	Integer	Number of functions (n) (only in v1.2 or later)
	Array	n function table entries (only in v1.2 or later)
Symbol table entry
0	Byte	Data type
1	Byte	Pen colour In v1.2 or later, the symbol is deleted if the pen colour has bit 5 set, and the lower four bits are ANDed with %1111.
2	Byte	Layer number In v1.0 and v1.1, the symbol is deleted if the layer number is 16.
3	Byte	Line type
4	Integer	Address in drawing definition
8	Integer	Length in drawing definition (ignored in later versions)
Window definition
0	Double	Left X coordinate
8	Double	Bottom Y coordinate
16	Double	Right X coordinate
24	Double	Top Y coordinate
Grid information
0	Double	X spacing
8	Double	Y spacing
16	Double	X angle
24	Double	Y angle
32	Integer	Grid snap
36	Integer	Parametric grid snap
Text information
0	Double	Text width
8	Double	Text height
16	Double	Butterfly limit
24	Integer	Text precision
Dimension information
0	Double	The text width for dimensions.
8	Double	The text height for dimensions.
16	Double	The arrow head size.
24	Double	Clearance gap
32	Integer	The current dimension style, which can be one of the following values: 0 for internal dimensions. 1 for external left dimensions. 2 for external right dimensions. 3 for external dimensions.
36	Integer	Use arrow heads for dimensions instead of slashes.
40	Integer	Are dimension tolerances enabled?
44	Integer	The dimension precision.
Line style information
0	Integer	Definition of user-defined line style 1.
4	Integer	Definition of user-defined line style 2.
8	Integer	Definition of user-defined line style 3.
12	Integer	Definition of user-defined line style 4.
Scalar table entry
0	Integer	The symbol number of the scalar.
4	Null-terminated string	The name of the scalar.
Error information
0	Integer	A value associated with the last error. The exact purpose depends on the identifier.
4	Null-terminated string	The identifier of the last error to occur.
Layer information (v1.0 and v1.1)
0	Array	16 bytes containing the status of each layer. If bit 0 is set then the layer is on. If bit 1 is set then the layer is locked.
16	Array	16 bytes containing the default pen colour for each layer.
32	Byte	The active current layer.
33	Array	10 bytes mapping each pen colour to a 16 colour palette entry.
Layer information (v1.2)
0	Array	64 bytes containing the status of each layer. If bit 0 is set then the layer is on. If bit 1 is set then the layer is locked.
64	Array	64 bytes containing the default pen colour for each layer.
128	Byte	The active current layer.
129	Byte	The active points layer.
130	Byte	The active construction layer.
131	Array	10 bytes mapping each pen colour to a 16 colour palette entry.
Function table entry (v1.2 or later)
0	Null-terminated string	The name of the function.
	Integer	The number of parameters.
	Integer	The address of the function in the definition block.

Drawing definition

The drawing definition is an array of opcodes. The return values are pushed in order to a stack, and the parameters are popped in reverse order. Some opcodes have extra data that is read in from the drawing definition and is used as the return value.

Code	Description	Parameters	Return value	Extra data
0	Push name	None	Integer	Integer
1
2
3
5	+	Double, Double	Double
6	-	Double, Double	Double
7	unary -	Double	Double
8	Start	Double, Double	None
9
10
11
12
13
14
15
16	To	Double, Double	None
17
18	Centre of	Double, Double	None
19	Clockwise	None	None
20	Anti-clockwise	None	None
21	Radius	Double	None
22
23
24	*	Double, Double	Double
25	/	Double, Double	Double
26	^	Double, Double	Double
27	sqrt	Double	Double
28	sin	Double	Double
29	cos	Double	Double
30	tan	Double	Double
31	asin	Double	Double
32	acos	Double	Double
33	atan	Double	Double
34	atan2	Double, Double	Double
35	abs	Double	Double
36	degrees	Double	Double
37	radians	Double	Double
38	Push integer	None	Integer	Integer
39	Push real	None	Double	Double
40	Eval ID	Integer
41	Arc from	Double, Double	None
42	Arc to	Double, Double	None
43	Push byte	None	Byte	Byte
44	Line tangent to 2 circles	Byte, Integer, Byte, Integer	None
45	Intersection of 2 lines	Integer, Integer	Double, Double
46	Intersection of line and circle	Byte, Integer, Integer	Double, Double
47	Construction line from 2 points	Double, Double, Double, Double	None
48	Angled construction line	Double, Double, Double	None
49	Construction line tangent to 2 circles	Byte, Integer, Byte, Integer	None
50	Parallel construction line	Integer, Double, Double	None
51	Perpendicular construction line	Integer, Double, Double	None
52	Centre of construction circle	Double, Double	None
53	Construction circle radius	Double	None
54	Construction circle diameter	Double	None
55	Intersection of 2 circles	Byte, Integer, Integer	Double, Double
56	Circle tangent to 2 lines	Byte, Integer, Integer, Double	None
57	Line tangent from point to circle	Double, Double, Byte, Byte, Integer	None
58
59	Distance between 2 points	Double, Double, Double, Double	Double
61	Push X coordinate	None	Double	Double
62	Push Y coordinate	None	Double	Double
63	Point at centre of construction circle	Integer	Double, Double
64	Line normal from point to circle	Byte, Integer, Double, Double	None
65	Point on line at distance	Double, Double, Double, Integer, Byte	Double, Double
66	Circle tangent to 2 circles	Double, Byte, Integer, Integer	None
67	Parallel construction line at distance	Double, Integer, Byte	None
68	Circle tangent to line and circle	Double, Byte, Integer, Integer	None
69	Line normal to 2 circles	Integer, Integer, Byte	None
70	3 point circle	Double, Double, Double, Double, Double, Double	None
71	Circle tangent to line	Double, Double, Integer	None
72	Line relative to line	Double, Double, Double, Integer	None
73	Polar line	Double, Double, Double, Double	None
74	Point at end of line	None	Double, Double
75	Line bisects 2 lines (mk1)	Integer, Integer, Byte	None
76	Mid point	Double, Double, Double, Double	Double, Double
77	Perpendicular bisector	Double, Double, Double, Double	None
78	Point at start of line	None	Double, Double
79	3 point arc	Double, Double, Double, Double, Double, Double	None
80	Point at centre of arc	Integer	Double, Double
81	Angle dimension	Integer, Integer	Double, Double, Double, Double, Double, Double, Double, Double
82	%	Double, Double	Double
83	Int/	Double, Double	Double
84	trunc	Double	Double
85	round	Double	Double
86	log	Double	Double
87	log10	Double	Double
88	exp	Double	Double
89	Point at distance around circle	Double, Double, Double, Double, Integer	Double
90	Angle between 2 lines	Integer, Integer, Byte	Double
91	Line bisects 2 lines (mk2)	Integer, Integer, Byte	None
92	angle from 3 points	Double, Double, Double, Double, Double, Double	Double
93	Circle info	Byte, Integer	Double
94	Relative point	Double, Double, Double, Double	Double, Double
95	Call function
96	Function return
97	Push function parameter
98	Ignore string	None	None	Null-terminated string
99	Push string	None	String	Null-terminated string
100	Random number	Double	Double
101	Point distance on circle	Double, Double, Double, Integer	Double, Double
102	Point at end of text	Double, Double, Double, Double, Double, Integer	Double, Double
103	Polar point	Double, Double, Double, Double	Double, Double
104	Point at start of arc	None	Double, Double
105	Point at end of arc	None	Double, Double
106	Angle from 2 points	Double, Double, Double, Double	Double
107	Point between 2 points	Double, Double, Double, Double, Double	Double, Double
254	Return	None	None
255	End of symbol	None	None