This week we start working on a new Houdini project.
The themes we explore this week.
The first thing we need to focus on is [View Mode].
Auto update]: When we change the value of a node in Houdini, it will automatically (and very quickly) update the effect on the screen.
[On mouse up]: When we change the value of a node in Houdini, it will only be updated when we click on the window with the mouse.
[Manual]: Manual update. This can be interpreted as updating the window effect independently when we change the value of the node. (This mode is very convenient, and I have been using this mode in my last assignment.)
The [Null] node: this node does not have any effect. But it is easier to create a [Null] node in the panel to observe the process. (Probably because the shape of this node is so unusual. Most of the other nodes are rectangular, whereas the [Null] node is an X-like shape)
When there are multiple nodes in the interface that need to be sorted, we can select [A] or [L] to quickly sort them.
[A]: After selecting all the nodes, press and hold [A], then drag and drop. The nodes will then be sorted automatically. (automatically arranged in a row)
[L]: After selecting all the nodes, press [L]. The nodes will also be sorted automatically. Unlike [A], [L] sorts the nodes into rows and columns of different values.
When we hold down [J] and [left mouse button], the dragged curves will form connections on the nodes. (In the Houdini interface, it is like stitching the nodes together with a needle and thread). When you need to delete a connection, hold down [Y] and [LEFT MOUSE BUTTON]. (In the Houdini interface, it looks like you are using scissors to cut the nodes). I have always used [Delete] after selecting a node.
Selecting multiple nodes is very similar to other software. [Shift] plus [Left mouse button] can add multiple selected nodes if you want to deselect a node, use [Ctrl] plus [Left mouse button].
We can select [Open display options] (shortcut is [D]) when our node appears [Warning]. In the [Network View Display Options], you can see the reasons for the different warnings.
In the animation module:
[Arrow key ↑] is to play
[Arrow key ↓] is to play in the opposite direction of the timeline
[Arrow key ←] is the previous keyframe of the animation
[Arrow key →] is the next keyframe of the animation
[Ctrl] + [Arrow key ←] is to reach the first keyframe of the animation
[Ctrl] + [Arrow key →] is the last keyframe of the animation
In the [i] property bar of the node, we can observe the values of [Points], [Primitives], [Vertices] and [Polygons].
To observe UVs.
Create [testgeometry_squab] and [UVquickshade]
Show [Points]
Click on [Display vertex markers]
In [UV View]:
In [Geometry Spreadsheet]:
【Geometry (SOP) networks】：
VOP Functions
VOP nodes let us define a program (such as a shader) by connecting nodes together. Houdini then compiles the node network into executable VEX code.
【VOP NODES】:
https://www.sidefx.com/docs/houdini/nodes/vop/index.html
VEX Functions
【VEX NODES】：
https://www.sidefx.com/docs/houdini/vex/functions/index.html
【Attribvop】：
【Noise】：
【Bind】：
【Bind VOP node】：
https://www.sidefx.com/docs/houdini/nodes/vop/bind.html
Start working on this week’s exercise [Particle]
The first thing to do is to create the [geometry] node.
This time we are using [testgeometry_crag] as the base model node.
Use the shortcut key [N] to change the mode (can be used instead of the menu).
[timeshift] can be used to freeze the frame.
Create the [popnet] node.
Always remember to turn off [Display Sprites] in the settings. Double click into the [popnet] node to observe the [testgeometry_crag] model.
Create a [Sphere] in [Polygon] mode. Connect [Sphere] with [popnet] and you can observe many points.
In the [Geo] screen, we cannot observe the [testgeometry_crag] model. This is because Houdini autonomously selects the entire face of the [testgeometry_crag] model when we select the model’s points individually. And [Sphere] can be operated by [popnet] because each point in [Sphere] is independent.
At this point, we can create a [pack] node. [pack] helps polygons to be recognized as a whole by Houdini. The [unpack] can be used when transforming geometry into polygons.
Add [unpack] to the node tree of [testgeometry_crag]. Transform [testgeometry_crag] from a geometry to a polygon.
Custom nodes in the [popnet] node:
【popobject】is will be like a container full of particles and that container will go through a popsolver.
【popsolver】think about it like a toolbox. A toolbox where you’re going to have. Everything you need to calculate what’s happening in dynamics, so it has physics operations. It has all the physics logic we need.
【popsource】can solving whatever physics we have.
The nodes in [popnet].
[gravity] is something that is common to all solvers.
Place [gravity] under [popsolver]. At this point, we can see that the particles on the [testgeometry_crag] model have a tendency to fall downwards.
【Wind】：
In【popnet】we have different types of winds.
For this project, we can use either [popwind] or [windforce], but there’s one specific limit for [Particles].
There is a very user-friendly design in the [popnet] panel. We can look at the colour of the nodes to place different nodes.
For example, if the node for [popwind] is purple, then we can connect [popwind] behind [source_first_input]. This is because the line behind [source_first_input] is also purple.
Increase the value of [Wind Velocity] in [popwind] and you will find that the particles will change the direction of movement.
(Reduce the value of [Cache Memory] in the [Cache] panel of [popnet]. This will help our computer to reduce the consumption of fast computing.)
Add the [Scatter] node to the [geo] panel. The [Scatter] node adds points to the object’s surface and changes the number and density of particles.
Go back to the [popnet] panel. We start adjusting [source_first_input] ([popsource]).
Adjust the mode of [Emission Type] in [Source] of [popsource].
[Points] mode:
[All Points] mode:
Looking at the effect, we select [Points] mode.
In [Birth] [Const. Birth Rate] you can change the speed of particle generation.
For the rendering time rate, [FPS24] is recommended. Checking [Integer Frame Values] will help the rendering to be closer to the real rate.
The value of [Const. Birth Rate] in my current file is [10000], which means that [10000] particles are created in every 24 frames.
[Render Flipbook]
Help with rendering Houdini files.
Create a [popforce] node. Changing the value of [Amplitude] in [popforce] can be similar to [noise wind] and can affect the direction of movement of the particles.
Add the [popdrag] node, which acts as a change in the resistance of the air. (Do some more sharper shapes if you want.)
Back in the [geo] panel, I’ve added [pointvelocity] and [delete]. The [pointvelocity] changes the speed of the particles, and [delete] is used to delete particles that affect the screen. I also adjusted the value of the nodes in [popnet].
(tip: Be sure to change the [Geometry Source] and [SOP] in [Popsource]. Select the path of [SOP] as [OUT_POP_SOURCE]. (Otherwise, you will need to use a line to connect the two nodes.)
Current node values:
【popobject】：
【popdrag】：
【popwind】：
【popforce1】：
【popforce2】：
【unpack】：
【pointvelocity】：
【scatter】：
【delete】：
【popnet】：
Added nodes:
【attribvop】：
【sphere】：
【copytopoints】：
Final node diagram:
Final rendering video: