Softimage XSI

Stretchy bones in ICE

Open the scene Stretchy_Bones from this issues DVD. Select the Stretchy_Bones null object and press [Alt] + [9] to open an ICE Tree. From the Create menu choose ICE Tree to create an empty ICE Tree. The idea of stretchy bones or limb stretching is quite simple. If the distance between the root and the effector is greater than the sum of the bones, the bones should stretch. But if the distance is less, the bones should stay unaffected at their default length.

Get a Get Data node and double-click on it to open its PPG. Click the Explorer button and expand the tree root > Kinematics > Global Transform and select the Pos. Get a second Get Data node and type eff.kine.global.pos in the Get Data textbox to get the position for the effector as well. The next step is to calculate the distance between the two objects, so get a Get Distance Between node. Connect the root.kine.global.pos node to the First input of the Get Distance Between node and the eff.kine.global.pos node to the Second input.

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Changing color of an objects based on its distance to another object

There are many instances where you want to be able to control an attribute of a shader based on its distance to the camera or another object in the scene. Regardless of the end effect you’re trying to achieve, the procedure of getting there is about the same.

Select any of the spheres (they all share the same material) and press [7] to open a Render Tree. From the Nodes > Conversions menu, get a Scalar to Vector node. This node enables you to enter any XYZ coordinates and by linking their separate values to the corresponding value of the Ctrl_Null, you’ve efficiently extracted the nulls position and made it available in the render tree. Open its PPG and click the Lock icon to pin it to the screen. Select the Ctrl_Null and press [Ctrl] + [K] to open its transform PPG. Drag the animation icon (the green divot) for the X Position (in the transform PPG) and drop it onto the animation icon of the Input X in the Scalar to Vector PPG. Repeat for the Y and Z position.

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Assigning different task based on condition

Select the particle_emitter and Simulate > ICE > Create menu choose Emit Particles from Selection… With the PointCloud still selected, press [Alt] + [9] to open an ICE Tree. Before you can assign any goal or paths for the particles you have to choose a criterion to use to separate the particles. In this example you’ll be using three different objects so it makes sense to divide the particles into three groups, one for each goal/curve. As each particle is born it’s also assigned a unique identification or ID. By feeding this ID into a Modulo operation and set the devisor to the same value as the number of groups you want to create, you’ve efficiently created the 3 collections.

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Painting weights in ICE

While the weights in the weight map will be controlled from within the ICE Tree, you have to create the actual weight map manually. Select the Grid object and from the Get > Property menu choose Weight Map. Select the Grid object and press [Alt]+[9] to open an ICE Tree and from the Create menu choose Simulated ICE Tree. Press [8] to open an Explorer and drag and drop the Sphere object to your ICE Tree. Continue by getting a Pass Trough node, a Get Point Position node and a Get Closest Location node. The Get Point Position node returns the position of each of the points of the grid which is then used by the Get Closest Location node to determine whether the Sphere touches any of the vertices of the grid object (or is within a specified distance). If the Sphere is within this value the corresponding points’ weight should be set 1. If it’s not, the weight should stay unaffected (the default value is zero). Open its PPG. Check the Enable Cutoff Distance checkbox and set the Cutoff Distance to 0.1 and close the PPG.

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Expanding the width of the rendered image without distorting the camera perspective

By changing the cameras position and increase the size of the output resolution you’ll obviously be able to widen the shot. Unfortunately you’ll end up with a completely different perspective. By compensating the cameras field of view angle in relation to the added pixels the expanded images will line up exactly with the original image when superimposed. The procedure will work just as well if you need to reduce the size of the image.

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How to fill a volume using rigid body dynamics in ICE

The standalone or default rigid body dynamics engine is the preferred solution if you’re simulating few or a fixed number of objects and need high precision. If you’re on the other hand are set to take on a large number or are adding new objects to the simulation over time then ICE would most likely be the one to choose. Even as booth engine uses the physX as the dynamics engine, ICE still isn’t the answer to all your upcoming simulation struggles. And the reason for this is quite simple. Kinematics isn’t officially supported within the ICE framework yet (though it can be activated manually) and the actual shape isn’t available as a collision type.

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Rigging a piston engine

The concept of a reciprocating engine, commonly referred to as a piston engine, is in fact quite simple. Petrol gets injected into the cylinder and the piston pushes upwards to compress the petrol (fumes). The spark plug sets of a spark which ignites the fumes and causes it to explode. The force of the explosion sends the piston down through the cylinder. The piston is connected to the crankshaft via a connecting rod, which transforms the up and down movement into a rotation motion which in the end drive the wheels of the car. The piston is connected in pairs so when one piston is pushed down the other is pushed up which compresses the fumes, which is then ignited by the spark plug and so on.

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Single axis direction constraint

As you’ve noticed there isn’t a one click solution to limit the direction constraint to a single axis. However there’s no need to despair as we’ve supplied you with two different methods to tackle the problem.

Open the scene Surveillance_Camera.scn from this issues DVD. The first method requires two null objects, one which can be moved in any direction and one that will be used for the actual direction constraint. Create a null object, name it Direction_Cns and move it somewhat in front of the surveillance camera. Create another null object, name it LookAt and move it in front of the camera as well. Press [Ctrl] + [K] to pen its Local Transforms PPG and click the Lock icon to pin it to the screen. Select the Direction_Cns object and press [Ctrl] + [K] to open its transform PPG as well.

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Assigning different textures to the same geometry-instances in ICE

While you can’t assign different materials to the same geometry instances per se, you can use attributes from the pointclod to achieve the same result. Start by open the scene multiple_textures.scn from this issues CD. Select the PointCloud and press [Alt] + [9] to open an ICE Tree. With the pointcloud and the instanced geometry already in place, the only thing left to add is a random color. Get a Randomize Color by Gradient node and connect it to the Color input of the Emit from Surface node. Open the Randomize Color by Gradient PPG and change gradient to match the screenshot.

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Water Condensation using ICE

On planet earth matter can traditionally exist in three physical states or forms; solid, liquid and gas. There are in fact a couple of more states such as plasma and liquid crystal, but let’s not get too technical. Condensation is essentially water changing it physical state of aggregation from gaseous into liquid (guess you’re glad we didn’t get in to the technical parts). One of the most common examples of this is the creation of clouds. As warm air rises to the atmosphere it cools and loses its ability to hold water vapor. The water molecules will then clump together to form cloud droplets, which then of course fall as rain (a phenomenon anyone who has visit England is far too familiar with).

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