BPT Bézier Patch and PatchOff Configuration File Formats

BPT Bézier Patch File Format

The BPT file format is a very simple text format. The first line consists of the number of patches the BPT file contains. Each patch record is followed immediately by the next, and consists of the following items. A single line, consisting of two ints. These are the u and v dimensions of the patch (e.g. 3 3 for a bicubic patch). Then, one control point per line, for u * v lines. The control points are three doubles, separated by spaces. Control points move along the first dimension specified first, then the second. Therefore, for a "1 2" patch, the first two would be the first edge, the next two would be the center, and the final two would be the far edge.

Format

<n - number of patches>
<u1> <v1>
<x0 0> <y0 0> <z0 0>
<x1 0> <y1 0> <z1 0>
.
.
.
<xu - 1 0> <yu - 1 0> <zu - 1  0>
<x0 1> <y0 1> <z0 1>
.
.
.
<xu - 1 v - 1> <yu - 1 v - 1> <zu - 1 v - 1>
<u2> <v2>
.
.
.
<un> <vn>
.
.
.
<xu - 1 v - 1> <yu - 1 v - 1> <zu - 1 v - 1>

Examples

These files contain multiple patches.

• teapotCGA.bpt - The teapot as defined in Computer Graphics & Applications, Volume 7, Number 1, January, 1987, pp 8-19. It has a bottom, but no rim on its lid.
• teapotCGAnobottom.bpt - The same teapot as above, but with the four patches of the bottom removed.
• teapotCGAtall.bpt - The CG&A teapot, scaled by 1.33333 to restore its height to the original version.
• teapotCGAnobottomtall.bpt - The same teapot as above, but with the four patches of the bottom removed.
• teapotrim.bpt - Another set of datapoints for the teapot, in a different scale. This one is also 32 patches, but instead of adding a bottom with the four patches, a rim has been added.
• teaspoon.bpt - Newell actually created a full teaset. This is supposedly the teaspoon from the set, from the web.
• teacup.bpt - Like the teaspoon above, this is supposedly the teacup from the set, from the web.
• heart.bpt - A heart, built by myself for testing purposes.
• sphere.bpt - An approximation to a sphere, also from CG& A.

PatchOff Configuration File Format

PatchOff takes a rigidly structured configuration file as input, and creates an OFF file from an input BPT file using the requested parameters. Each parameter must be on its own line, and is case sensitive. Improper parameters will default, so if PatchOff is not behaving as expected, check spelling and capitalization. The five parameters are:

• Whether PatchOff should generate the mesh of the patch (MESH), the points and lines of the control net (CONTROL) or both (BOTH).
• Whether PatchOff should create an OFF file with per-vertex normals (Using the partial derivatives of the patch) (GENNORMALS) or not (NONORMALS).
• Whether PatchOff generates quadrilaterals (QUAD) or triangles (TRIANGLE) when evaluating the patches. Note that quadrilaterals may not be planar.
• The number of segments along the u-direction (int) (Must be 1 or more).
• The number of segments along the v-direction (int) (Must be 1 or more).

Format

MESH | CONTROL | BOTH
GENNORMALS | NONORMALS
QUAD | TRIANGLE
<segments in u>
<segments in v>

Examples

MESH
GENNORMALS
QUAD
3
3

MESH
NONORMALS
TRIANGLE
8
8