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Creating LDraw Parts:
LDraw file format
LDraw File Format
File Extensions
LDraw Model files
carry either the extension LDR (default) or DAT. LDraw Part Files
carry the extension DAT.
Text-Based
LDraw files are plain
text. Each line is a single command, and each line is independent.
Only a few commands are used in the file format. Specific commands
are identified by the first number on the line, which is called the
line-type. The contents and format of the rest of the line
depend on the line-type. No length-limit on command lines is known.
Line types
Each line in the file
is a single command. The first number on each line is the line type,
valid values are 0 through 5, with the following meanings:
- 0:
- comment or meta-command
- 1:
- Part-file reference
- 2:
- Line
- 3:
- Triangle
- 4:
- Quadrilateral
- 5:
- Draws a line between the first two points, if the last two
points are on the same side of that line.
If the line type for a line is not a valid value, the line is
ignored.
Meta-commands require a keyword to follow the line-type. These
keywords must be in all-caps, and you should assume that if the
meta-command doesn't require more information, you shouldn't give it
any additional information.
Commands
Here is a complete list
of LDraw drawing- and meta-commands:
- Model Title
- Step
- Write
- Clear
- Pause
- Save
- Comment
- Part
- Line
- Triangle
- Quadrilateral
- Conditional-Line
And here are the details of each command. Meta-commands are
listed first, with the "real" commands after. The command-names are
wholly made up by me, I don't have any "official" names for these
things.
- Model Title.
- The descriptive name of the model- or part-file.
- Line format:
0 title-text where title-text is
whatever you want to name your model.
- This is a meta-command, sort of. If the first line in a file
has line-type 0, the remainder of that line will be considered the
title for the file (at least for parts files). This overrides any
meta-commands on the line.
- Step meta-command.
- Marks the end of a building step.
- Line format:
0 STEP
- This command will cause LDraw (ldraw.exe) to stop until you
press <enter>, and it will cause LDraw to save the current
image into a bitmap file in the
ldraw\bitmap
directory. These two effects are controlled by the -M
command line option (see ldraw.doc for info on
-M).
- Write meta-command.
- Displays a message at the top of the screen.
- Line format:
0 WRITE message-text
- or:
0 PRINT message-text where message-text
is whatever you want displayed on the screen.
- The displayed message is not saved in the image-bitmap files.
- Clear meta-command.
- Clears the screen.
- Line format:
0 CLEAR
- Useful for advanced model files. Don't forget to redraw all
the parts you just erased by using this command.
- Pause meta-command.
- Causes LDraw to stop until you press <enter>.
- Line format:
0 PAUSE
- This is like the Step command, but it does not save bitmaps,
and it is not affected by the
-M command line option.
- Save meta-command.
- Causes LDraw (ldraw.exe) to save the current image in a
bitmap.
- Line format:
0 SAVE
- This is also like the Step command, but it does not cause
LDraw to pause, and it is not affected by the
-M
command line option.
- Part command.
- Inserts a part defined in another LDraw file.
- Line format:
1 colour x y z a b c d e f g h i part.dat
where
- colour is a colour code: 0-15, 16, 24, 32-47, 256-511
- x, y, z is the position of the part
- a - i are orientation & scaling parameters (see below
for more on this)
- part.dat is the filename of the included file
- Parts may located in the
p\, parts\,
or models\ subdirectories (under the
ldraw\ directory). They may also be located in the
current directory. James has arranged the directories so that
p\ contains elements that are intended to be used as
part of elements (such as stud.dat). The
parts\ directory contains finished parts, ready to be
used in construction models. And the models\
directory contains construction models.
- Part files can also include Part commands. There don't seem to
be a specific limit to how deep these references can go.
- Line command.
- Draws a line between two points.
- Line format:
2 colour x1 y1 z1 x2 y2 z2 where
- colour is a colour code: 0-15, 16, 24, 32-47, 256-511
- x1, y1, z1 is the position of the first point
- x2, y2, z2 is the position of the second point
- Triangle command.
- Draws a filled triangle between three points.
- Line format:
3 colour x1 y1 z1 x2 y2 z2 x3 y3 z3
where
- colour is a colour code: 0-15, 16, 24, 32-47, 256-511
- x1, y1, z1 is the position of the first point
- x2, y2, z2 is the position of the second point
- x3, y3, z3 is the position of the third point
- Quadrilateral command.
- Draws a four-sided, filled shape between four points.
- Line format:
4 colour x1 y1 z1 x2 y2 z2 x3 y3 z3 x4 y4 z4
where
- colour is a colour code: 0-15, 16, 24, 32-47, 256-511
- x1, y1, z1 is the position of the first point
- x2, y2, z2 is the position of the second point
- x3, y3, z3 is the position of the third point
- x4, y4, z4 is the position of the fourth point
- Conditional-Line command.
- Draws a line between the first two points, if the projections
of the last two points onto the screen are on the same side of an
imaginary line through the projections of the first two points
onto the screen.
- Line format:
5 colour x1 y1 z1 x2 y2 z2 x3 y3 z3 x4 y4 z4
where
- colour is a colour code: 0-15, 16, 24, 32-47, 256-511
- x1, y1, z1 is the position of the first point
- x2, y2, z2 is the position of the second point
- x3, y3, z3 is the position of the third point
- x4, y4, z4 is the position of the fourth point
Colours
Colours are outlined in
LEDIT.DOC. Two special values are 16 and 24. 16 is the 'current
colour', i.e., whatever colour was specified on the type 1 line
which caused the current line to be executed. Colour 24 is a
complementary colour to the current colour, usually the bright/dark
complementary shade. So if the current colour is dark blue, colour
24 would give bright blue.
Also, colours 256 through 511 are dithered. So if you want to
combine colours J and K, figure your colour value as colour = (J * 16) + K + 256
The complementary colour of J is used as the complementary colour
of the dithered value. So you can control the edge colour (somewhat)
by switching J and K.
Format of Linetype 1
The Part
command (linetype 1) has some unique features that require special
attention. This section makes more sense if you're familiar with
matrix math. It makes much more sense if you're familiar with using
matrix math in graphic modeling.
- Line Format:
1 colour x y z a b c d e f g h i part.dat
Fields a through i are orientation & scaling parameters,
which can be used in 'standard' 3D transformation matrices. Fields
x, y and z also fit into this matrix: | a d g 0 |
| b e h 0 |
| c f i 0 |
| x y z 1 |
so that every point (x, y ,z) gets transformed to (x', y', z') :
x' = a*x + b*y + c*z + x
y' = d*x + e*y + f*z + y
z' = g*x + h*y + i*z + z
or, in matrix-math style: | a d g 0 |
| X' Y' Z' 1 | = | X Y Z 1 | x | b e h 0 |
| c f i 0 |
| x y z 1 |
Explanation of Conditional Lines (Linetype
5)
Here is an example using the conditional line command.
If we try to approximate a (cylindrical) stud with a hexagonal prism
we have something like this: 1___________2
/ \
/ \
6/ \3
|\ /|
| \ / |
| \5___________4/ |
\ | | /
\ | | /
\|___________|/
- The line below 1 should not be drawn because 6 and 2
are on different sides.
- The line below 2 should not be drawn because 1 and 3
are on different sides.
- The line below 3 should be drawn because 2 and 4 are on
the same side.
- The line below 4 should not be drawn because 3 and 5
are on different sides.
- The line below 5 should not be drawn because 4 and 6
are on different sides.
- The line below 6 should be drawn because 5 and 1 are on
the same side.
resulting in the following drawing: 1___________2
/ \
/ \
6/ \3
|\ /|
| \ / |
| \5___________4/ |
\ /
\ /
\_____________/
For questions, contact Steve
Bliss.
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