Resources Numerical accuracy Calculation policy
Reads and writes Wavefront OBJ files: points, faces, texture coordinates and normals as text, in meters with Y up.
On import each number in the text is parsed to a 64-bit number and stored as it is, with the axes swapped. On export every coordinate, texture coordinate and normal is printed with 6 decimals, so an exported point is rounded to 0.000001 m.
Open item. Print exported coordinates with the shortest text that reads back to the same 64-bit number instead of 6 decimals.
6 calculations in 1 source file. The code is read from the released app when this page loads. It is the calculation people run, not a copy kept for this page.
Tests tools/modelcraft-test/meshfiles.mjs
Parses the three coordinates of a 'v' line.
Each number is converted from text to the nearest 64-bit number and kept unrounded. A coordinate that is not finite or is 1e7 or more in size refuses the file.
if (tag === 'v') {
const x = +parts[1]; const y = +parts[2]; const z = +parts[3];
if (![x, y, z].every((q) => Number.isFinite(q) && Math.abs(q) < 1e7)) throw fail(t('obj.why.vertex', { line: lineNo }));
P.push(x, y, z);Copies an object's points into the model's coordinates.
(x, y, z) → (x, −z, y)
A swap and a sign change; the points then go into a Float64Array. No unit factor is applied: the file is read as meters.
if (k === undefined) { k = pts.length / 3; local.set(v, k); pts.push(obj.positions[v * 3], -obj.positions[v * 3 + 2], obj.positions[v * 3 + 1]); }Marks an edge sharp where the file's normals break across it, where smoothing groups differ, or where the faces bend.
with normals: sharp unless n₁ · n₂ > 0.9995 at both ends; without normals or groups: sharp when the face normals' dot product < 0.99996
0.9995 is the cosine of about 1.8° and 0.99996 of about 0.5°. The corner normals compared are read from the mesh's 32-bit 'normal' layer.
/** Sharp where the corner normals break across an edge; with no normals, between smoothing groups (0 = off: all sharp). */
export function markSharp(mesh, N, smoothOf = null) {
const { hTw, hNx, hFl, hF } = mesh;
const has = (a) => N && (N[a * 3] !== 0 || N[a * 3 + 1] !== 0 || N[a * 3 + 2] !== 0);
const same = (a, b) => N[a * 3] * N[b * 3] + N[a * 3 + 1] * N[b * 3 + 1] + N[a * 3 + 2] * N[b * 3 + 2] > 0.9995;
for (let h = 0; h < mesh.nh; h++) {
const g = hTw[h];
if (g < 0 || g < h) continue;
let sharp;
if (has(h) && has(g) && has(hNx[h]) && has(hNx[g])) sharp = !same(h, hNx[g]) || !same(hNx[h], g);
else if (smoothOf) { const a = smoothOf[hF[h]]; const b = smoothOf[hF[g]]; sharp = !a || !b || a !== b; }
else { const na = mesh.faceNormal(hF[h]); const nb = mesh.faceNormal(hF[g]); sharp = na[0] * nb[0] + na[1] * nb[1] + na[2] * nb[2] < 0.99996; }
if (sharp) { hFl[h] |= FL_SHARP; hFl[g] |= FL_SHARP; }
}
}Prints a number for the exported file.
text = the number rounded to 6 decimals, trailing zeros removed
toFixed(6) rounds every exported coordinate to 0.000001 m, and texture coordinates and normals to 6 decimals. This is a rounding of the exported value, not of a display.
const f6 = (x) => { const v = +x.toFixed(6); return Object.is(v, -0) ? '0' : String(v); };Carries a mesh point to world coordinates and Y up for the file.
p′ = placement matrix × p; (x, y, z) → (x, z, −y)
The world point is 64-bit; it is rounded only when printed by f6. Faces of a mirrored placement (negative determinant) are written in reverse order.
const V = (v) => { if (!vmap.has(v)) { vmap.set(v, vBase + vs.length); vs.push(zy(apply(wm, [M.P[v * 3], M.P[v * 3 + 1], M.P[v * 3 + 2]]))); } return vmap.get(v); };Applies a material's map scale and offset to a texture coordinate on import.
u′ = u × scale_u + offset_u; v′ = v × scale_v + offset_v
Computed in 64-bit and stored in the mesh's 32-bit 'uv' layer, which places a picture and is not a measured value.
if (UV && f.t[q] >= 0) { UV[h * 2] = obj.uvs[f.t[q] * 2] * sc[0] + of[0]; UV[h * 2 + 1] = obj.uvs[f.t[q] * 2 + 1] * sc[1] + of[1]; }Every value is a 64-bit number from input to result. Formulas are closed form or a direct solve, and every comparison uses a stated tolerance.