Alex Majewski

alexmajewski

About Me

EXPERTISE
Developer
INDUSTRY
Advertising / Motion Graphics

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LOCATION
Poznan, Not Specified
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Houdini Skills

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Recent Forum Posts

Houdini FX rendering on multiple computers June 18, 2025, 4:56 p.m.

Hqueue and Deadline are the proper solution, but at least Deadline should not be advised without first asking if you have ever used it (as an artist). If not, this is going to be a disaster unless you have someone to help you understand what you're doing. Or unless you're a very persistent and technical person.

If you end up hitting a wall, the simplest way of using your Karma licenses is by manually rendering with Husk. This can be automated with simple scripts.

How to switch multiple viewer states in HDA? May 21, 2025, 5 p.m.

I'm learning Python viewer states and I'm trying to find out if and how can I switch between states.
Let's say we have 3 wildly different modes/states in our tool, and we'd like to have three separate state classes that we toggle with hotkeys.

Is that possible? I'm specifically asking about keeping the logic of those modes/states in separate sections of code. Three separate __init__(), onEnter(), onMouseEvent(), etc. in a single HDA.

Vex: How to proportionally conform a shape to rectangle? May 17, 2025, 4:15 a.m.

Thank you both very creative solutions that will fit 99% of use cases. The spark that ignited my question was trying to get a triangulated cone-shaped flower petal to have a rectangular UV.

I was fishing for a vex solution in the title, because the described situation is only the first step and I was going to expand this problem. What if we wanted to straighten only the sides and not the top and bottom parts of the island? What if we wanted the corner points to be arbitrary and exist only as a Python state in the viewport?

I'm basically trying to create a UV space lattice.

Yesterday I learned about quadrilateral interpolation [www.reedbeta.com]. I'm not a math person, so I only understand the core concept.

Here's what I got so far. I work on a point attribute UV to make it easier for myself for now.
The first point wrangle calculates the local uv of each point that will be used to recreate its position with interpolation
// corner points clockwise
i@pt0 = 90;
i@pt1 = 99;
i@pt2 = 9;
i@pt3 = 0;

float wedge2d(vector a; vector b) {
    return a.x * b.y - a.y * b.x;
}

vector2 invert_bilinear(vector p0, p1, p2, p3; vector q)
{
    vector b1 = p1 - p0;
    vector b2 = p3 - p0;
    vector b3 = p0 - p1 - p3 + p2;

    float A = wedge2d(b2, b3);
    float B = wedge2d(b3, q) - wedge2d(b1, b2);
    float C = wedge2d(b1, q);

    float v;
    if (abs(A) < 1e-5) {
        v = -C / B;
    } else {
        float discrim = B*B - 4*A*C;
        v = 0.5 * (-B + sqrt(discrim)) / A;
    }

    vector denom = b1 + v * b3;
    float u;
    if (abs(denom.x) > abs(denom.y))
        u = (q.x - b2.x * v) / denom.x;
    else
        u = (q.y - b2.y * v) / denom.y;

    return set(u, v);
}


vector uv0 = point(0, "uv", i@pt0);
vector uv1 = point(0, "uv", i@pt1);
vector uv2 = point(0, "uv", i@pt2);
vector uv3 = point(0, "uv", i@pt3);

vector q = v@uv - uv0;

u@local_uv = invert_bilinear(uv0, uv1, uv2, uv3, q);

Then I displace my corners.

Then in another point wrangle I apply the interpolation against my new corner positions:
vector uv0 = point(0, "uv", i@pt0);
vector uv1 = point(0, "uv", i@pt1);
vector uv2 = point(0, "uv", i@pt2);
vector uv3 = point(0, "uv", i@pt3);

vector pu0 = lerp(uv0, uv1, u@local_uv.x);
vector pu1 = lerp(uv3, uv2, u@local_uv.x);
vector new_uv = lerp(pu0, pu1, u@local_uv.y);

v@uv = new_uv;

So far it seems to work perfectly as long as the affected UV points are between the 4 points.

So my current workflow would involve straightening desired edges with UV Flatten and then stretching them with vex. At least, as long as I don't figure out how to straighten them with vex. I'm attaching a hip.
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