Primitives Reference: Difference between revisions
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| [[File:4-4ring1.png|200px|thumb|alt=1-4ring1]] | | [[File:4-4ring1.png|200px|thumb|alt=1-4ring1]] | ||
|| This suite of primitives are used to generate circular rings or part rings. The numeric suffix r in the filename indicates the inner radius of the ring - the outer radius is 1LDu greater. For example a n-f4-4ring4 primitive would create a ring with an inner radius of 4LDu and an outer radius of 5LDu. | || This suite of primitives are used to generate circular rings or part rings. The numeric suffix r in the filename indicates the inner radius of the ring - the outer radius is 1LDu greater. For example a n-f4-4ring4 primitive would create a ring with an inner radius of 4LDu and an outer radius of 5LDu. | ||
Note: The correct nomenclature is to use the full word "ring". All newly created ring primitives must use "ring". Due to the fact that too many files would be affected, it was decided to keep the current official "rin" primitives in the library. All files using "ri" have been moved, to use "ring". | |||
''Currently available primitives:''<br> | ''Currently available primitives:''<br> | ||
Revision as of 14:31, 3 December 2023
LDraw Primitives Reference
This page is a source of reference for the LDraw primitives in the \LDraw\p directory. Primitives are defined as highly re-usable components of LEGO parts modelled for LDraw. They serve several purposes :
- To speed up parts authoring by providing a library of components which can be incorporated into several parts
- To allow rendering software to make substitutions of curved components
Within this reference material the available primitives are categorised into:
Each section contains an overview of the characteristics common to all primitives within that category. Primitives are grouped into classes within each category - one class of primitive serving a similar purpose at different sizes or resolutions. For each class of primitive, a brief description of the purpose of the primitive is provided, with notes on its co-ordinate origin, default size and rules for scaling. A list of the available primitives is shown.
An understanding of the orientation of the co-ordinate axes is essential for authoring a part for LDraw. For reference within this page the axes and their direction is shown in this diagram.
Rectilinear primitives
Nomenclature
Boxes are named boxF, with F representing the number of faces a box has. The suffix E represents the number of edges removed.
F and E are may followed by an additional letter. The hyphen is removed if F is accompanied by a modifier.
Face modifiers:
- o - faces are opposite to each other
- t - faces are all touching each other (usually, it's implied, but box4t.dat is a thing)
- u - missing faces form a U-shape
Edge letters:
- p - groups of edges are parallel to each other
- a - some missing faces have no adjacent edges
Scaling and orientation
These rectilinear elements may be scaled in the {x}, {y} and {z} dimensions to make elements of any size. For example
1 16 0 0 0 40 0 0 0 1 0 0 0 20 rect.dat
would generate a 80LDu x 40LDu rectangle in the {x,z} plane.
Although the default orientation of the rect.dat primitive is in the {x,z} plane the LDraw language allows for this to be transformed
1 16 0 0 0 0 1 0 40 0 0 0 0 20 rect.dat
would generate a 80LDu x 40LDu rectangle in the {y,z} plane.
1 16 0 0 0 40 0 0 0 0 20 0 1 0 rect.dat
would generate a 80LDu x 40LDu rectangle in the {x,y} plane.
Curved primitives
LDraw represents curved surfaces as polygons. For circular components two series of primitives are provided.
All the circular primitives are orientated in the {x,z} plane with their origin at the centre of the circle and a default radius of 1 LDu. Primitives are provided for complete circles and for commonly used fractions of a complete circle. Where the naming convention includes a prefix of the form n-f this indicates the fraction (n/f) of the circle drawn by the primitive. Where this fraction is less than an entire circle, the primitive starts at {+x,0} and progresses in a conterclockwise direction when viewed from above {-y}.
To avoid rounding errors, it is preferable to use existing fractional circular primitives, or create a new primitive, rather than rotate an existing primitive by anything other than 90 or 180 degrees. For example, use 3-16XXXX.dat rather than combining 1-8XXXX.dat with 1-16XXXX.dat rotated by 22.5 degreees.
To avoid matrix arithmetic problems in some renderers, the third dimension ({y} in the default orientation) of two-dimensional primitives must be given a non-zero scaling factor. LDraw circles are normally formed of 16-sided polygons (hexdecagons) - the regular resolution. For larger elements, where scaling-up of hexadecagons would give too angular an appearance, a series of high resolution primitives based on a 48-sided polygon are available. These may also be used for parts not well suited to a 16-fold symmetry.
These circular elements may be scaled by the same factor in both the {x} and {z} dimensions to make circular elements of greater or less than 1LDu radius. For example
1 16 0 0 0 3 0 0 0 1 0 0 0 3 4-4edge.dat
would generate a circle in the {x,z} plane with a radius of 3LDu.
They may also be scaled asymmetrically in the x and z dimension to make ellipses.
Although the default orientation is in the {x,z} plane the LDraw language allows for these to be transformed
1 16 0 0 0 0 1 0 3 0 0 0 0 3 4-4edge.dat would generate a circle in the {y,z} plane
1 16 0 0 0 3 0 0 0 0 3 0 1 0 4-4edge.dat would generate a circle in the {x,y} plane








































































