BlockCAD technical info

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The brick data for BlockCAD can be contained in many places, important files from the beginning are blockcad.ini and parts.dat, later on you may have any number of part files with any name:

• Some brick types are hardcoded into the program (for faster drawing). Those are the bricks with descriptions like '2x2x3' or 'W 2x4x6' etc. (see BrickTypes). You can edit the dimensions of this kind of brick, and add new bricks with your favourite length, width or height (not limited to the real Lego sizes) by right clicking in the selection list.
• The rest of the pieces have a description like 'G parts.dat, stdblock' (that's G <file name>, <part name>). These need a complete description in the indicated file (Details). You can create and edit those (in all aspects) by right clicking in the selection list.
• The selection pages themselves are defined in blockcad.ini, in a straightforward (at least I think so) format (Example), and you can add new pages, and remove empty pages by right clicking in the selection list.
• The conversion to Ldraw .DAT files needs a conversion table, bc2ld.lst.

BlockCAD has a couple of limitations, which (as far as I see) never will go away:

• Although you can create, and draw, bricks that are concave (eg. an L-shaped brick), you can never place another brick in the concavity, and have it drawn correctly. This is so, because all drawing is done on a per-brick basis, and an L-brick, with another brick inside the L really needs to be split in two parts - one part to be drawn before the other brick, one part to be drawn after.
• A corollary to this is that Lego Technic pieces cannot be introduced in BlockCAD, as they depend heavily on concavities - all the holes etc.
• The bricks can only be placed in strict positions and orientations - not arbitrary.
• All the bricks are studs-on-top, you cannot align them in any other direction.
• When you have more than a certain amount of bricks in your model, rotations are beginning to get real slow, and crossing an octant border adds a noticeable delay. The number depends on the speed of the computer - on my P233/64M I have drawn models up to 2000 bricks (my home), without much trouble, but of course it is a bit slow! Turning the stud drawing off before rotation helps a long way.
• Due to the fact that visibility 'calculations' are done on an Octant basis, some pieces can never be displayed correctly in all possible viewing directions. Examples of this are the 'Roof corner' and 'Inverted roof corner'. These need in fact a 'half octant' subdivision to be correctly drawn. What I really need, is a visibility calculation per surface, according to viewing angles, but that is an entirely new program.

There are also some more short term limitations, which I hope to remove sometime in the future:

• No export possibilites - I want to have export to Ldraw, and the POVRay ray tracing program
  Update: Version 1.4 adds a beta variant of Ldraw export. Version 1.5 can export to POVRay thanks to the L2P library by Lutz Uhlmann, or the L3P program by Lars Hassing.
• The drawing order of the blocks is not always correct (but pressing the 'brush' button one or more times fixes that in most cases)
• The sorting when rotating beyond an octant border is very slow
• There is never enough types of bricks

Hardcoded brick types

All those brick descriptions look like <type indicator> <length>x<width>x<height>. The length and width are measured in one-stud pieces, the height is measured in plates (i.e a standard brick has a height of three).

• <blank> or B - standard brick
• T - sloped brick (roof)
• N - roof top
• E - roof top end
• C - roof corner
• I - roof top corner
• R - round block
• W - window
• D - door
• O - wheel (kind of!)
• M - subassembly file

Sample blockcad.ini

There can also be an alternate display name after a vertical bar '|' on the brick descriptions. The idea is to note the actual Ldraw part identity here, so you have a chance to use only the pieces that can be drawn in Ldraw.

For the M-lines to work correcly, You have to add a bitmap (.bmp) to the same directory as the model is in. Don't make the bitmap too large!

Sample parts.dat

The general bricks use higher resolution coordinates, a one stud piece (1x1x3) is 20x20x24 here. The octant is the current viewing direction. For bricks that are transparent, you really need to draw every surface, irrespective of the viewing octant, for opaque bricks you can optimise by only drawing the visible surfaces. The ordering of the surfaces is important, you must give them in an order that guarantees that a surface that can occlude another is drawn after it. On bricks with many slopes in different directions this might well be impossible (use Ldraw instead)!

In some of the brick descriptions you might see another parameter 'LD=2'. This tells the program that this brick needs special handling when converting to Ldraw format. As the conversion routines are in the program code, you have no possibility to add another 'conversion special', so you should never use this (unless you have the source code of course).

  isaksson.etuna@ebox.tninet.se