viewer fails to generate normals for some shapes

[alexneufeld]

fidget-viewer test.rhai

// test.rhai

fn sdBox(x, y, z, xlen, ylen, zlen) {
    let qx = abs(x) - xlen;
    let qy = abs(y) - ylen;
    let qz = abs(z) - zlen;
    let qxm = max(qx, 0.0);
    let qym = max(qy, 0.0);
    let qzm = max(qz, 0.0);
    let qlen = sqrt(square(qxm) + square(qym) + square(qzm));
    qlen + min(max(qy, max(qx, qz)), 0.0)
}

let mybox = sdBox(x, y, z, 0.5, 0.5, 0.5);

draw(mybox);

rendering this script with the viewer demo in 3D heightmap and 2D SDF mode works as expected, but the 3D color mode produces no output. Running fidget-cli mesh -i test.rhai -o test.stl -d 6 also produces no useable output. This is probably a stupid error on my part; if not, let me know what other info to provide for debugging.

Thanks!

[mkeeter]

Hello!

This shape does not have well-defined partial derivatives near the surface, which is necessary to render normals. Specifically, it takes sqrt(0.0), whose partial derivatives are undefined and return NaN.

See #15, #127, #194