GET YOUR HEAD AROUND A PROCEDURAL WORKFLOW
Pluralsight’s John Moncrief has these tips for understanding the how and why of a procedural workflow in Houdini, via a proposed ‘window maker’ tool as part of building a skyscraper
You should think of a procedural workflow as a set of inputs driving multiple possible outcomes. It’s a system of instructions rather than a result. In this way Houdini becomes a ‘tool building tool’ rather than just a modelling, animation or simulation tool. For example, let’s say you are creating a skyscraper and you need to create 1,000 windows of varying widths and heights to go into this large building. Since all the windows are in the same building, they more than likely will all be of the same basic design style. So, instead of painstakingly modelling 1,000 windows (one for each hole in the wall of the building), why not make a Window Maker Tool for this task?
Inputs for your WINDOW 01
The input to the tool could be the width and height of the desired window. The tool (your procedural system) will take that information and generate a window with the specific number of window panes needed. For example, each pane of glass can be no larger than two metres in height and three metres in width. For the first hole in the wall the window needs to be six metres by six metres, so we use our Window Maker Tool to draw two ‘input’ curves, one for height, and one for width.
snapping points 02
With snapping on, just snap the first and last points of the curve to the righthand side of the window. To find out how many window panes to generate, all the system needs to do is divide the input height and width by the maximum size a window pane can be.
use The arclen() expression 03
For this example, we use the arclen() expression to measure the length of the curve we just snapped into place to find out that our hole is six metres tall.
DIVIDE The height curve 04
We use the value on our Control node to set the maximum height of a single window pane to two metres. Now six divided by two is three; we need three window panes, so we divide the height curve into three segments.
give The WINDOW Depth 05
The same theory applies for the width. After you have the width and height curve segmented properly and skinned, it’s just a matter of using a couple of extrudes to give the window depth. Once the system/ tool is built you can apply it to any hole in the wall that needs a window. Draw two simple curves, and it will create the needed window panes to fill it! Houdini makes its procedural nature portable by enabling you to build a procedural system, create a simple user interface, save that system to disk, and use it in another 3D application.
adjustments & DIRECTABILITY 06
Suppose your art director wants something changed with the windows; say that the maximum size for a window pane can now be four metres in height. Since you built a procedural tool based on a simple set of instructions, all you must do now is make one adjustment. Just tell the system that the max height is now three metres and it will push the change to all 1,000 windows. In our first system, we had one of the 1,000 holes in the wall that needed a six-metretall window, and our max window pane height was 2. 6 / 2 = 3. Now if that changes the max height of a window pane can now be 3. 6 / 3 = 2. The system will generate two window panes at three metres tall instead of three window panes two metres tall.
Because you used the procedural system, this one change (the max height of the window pane) is replicated in every use of the tool (every window hole, regardless of its size). So no matter if the hole in the wall was six metres tall (two window panes, three metres in height), or 27 metres tall (nine window panes, three metres in height), or 300 metres tall (100 window panes, three metres in height), it doesn’t matter, you don’t have to do any remodelling – just update the system with the new instructions.