by May 15, 2007 0 comments

In the last issue, we worked with the modeling features of Softimage XSI, and although the software provided with loads of options, I was disappointed by its poor interaction model. Continuing the series from last time, this time I explored the animation features to see how the animation in XSI worked out. Animation is an extremely important function in the overall development of a video. The main job of an animator is to make the modeled object move as a similar object would move in the real world.

The scene

I will prepare a simple animation scene, to get control over the movement of a bouncing ball. As I am mainly focusing on the animation, hence I would not waste my time modeling the ball.

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In the Get menu, click on Primitive, navigate to Polygon mesh menu and click on Soccer ball. A soccer ball would be created in all the four display ports and an options box would pop up. Close the options box without changing anything and press “F” to get the ball in focus in all the four viewports to get better control over the ball.

Adding animation expressions
Adding animation expressions provides the object to behave and move in the defined way. Usually expressions are equations which need to be learned and mastered to get the best possible animation effects.

In the toolbar, go to View > General and click on XSI explorer. A box would pop up with the object on the right side and a windows explorer interface on the left. In the explorer expand the soccer ball options by clicking on the “+” sign next to it, and from the expanded menu, expand the Kinematics menu. Double click on the Local transform icon; this brings up another box with various options. There in the position settings go to the Y axis and right click. From the pop up menu select “Set expression”, the expression editor box would pop up. Now in the expression editor box, type in “sin( ( Fc * 4 ) * 7 )” and then click on Validate. Once the equation gets validated, press Apply to add this expression to your soccer ball. Do not close the expression box as it is to be used a lot, simply minimize it.

Once the soccer ball is created, it can then be resized, moved or rotated as needed from any of the 4 viewports The animation graph displays the value of the movement of the object. Make sure you don’t have any negative values

Removing the negative bounce

After the above steps have been completed, your soccer ball has been animated to some extent, click on the play button to see the ball move up and down. However to get a better realistic animation, we need to edit the bounce. The graph editor helps in discarding of any bounce in the negative directions.

In the expression editor, go to the view toolbar and select show graph to display the animation graph. It would seem as a zig zag line going up and down over a scale, here you can see that the value is also going into negative. To stop this, change the equation to “abs(sin( ( Fc * 4 ) * 7 ))” and then validate and apply it. This would change the negative values to positive ones and double the already positive values to make up the space for the new values.

Control the jump
To control the bounce of the ball, Press F2 to get into the Animate mode and in the create subhead click on Parameter > New custom parameter set. In the box that pops up, name the parameter to anything, I have named it “Power”. Now again go to Create > Parameter and select New custom parameter this time, this time you would have to set the values. Change the default value to 7 and change the range value from 4 -30 for minimum and maximum respectively.

Now in the expression editor and change the equation to “abs(sin(( Fc * 4 ) * SoccerBall.power.param))”, again validate and apply it. Now again open the XSI explorer and you will be able to see a “C” icon denoting the custom parameter just created. Double click on it and you can change the bounce according to the value you enter in the pop up box.

You would notice that although the ball is jumping it is not working as a ball in real life. To correct this we add a second
parameter. To do this in the Explorer, select Speed, and then click on the right-hand bar, go to the Create subhead and click on
Parameter > New custom parameter. Name it Speed and change the default value to 8 and the minimum and maximum value to 1 and 30 respectively. In the expression editor, change
the equation to “abs(sin( (Fc * SoccerBall.power.speed)
* SoccerBall.power.param))“. Again validate it and apply it.

Now in the XSI explorer, double click the “C” icon which
denotes both the custom parameters and you would see that there are two value sliders there. You can control both the speed and height of the bounce using these two sliders.

The XSI explorer works similar to windows explorer. The custom parameter which is added is visible as a big “C” icon in it The preview window displays the final output. Once the animation is rendered, it is saved in the default project folder


To finalize the animation we will create a third parameter to
control its directional movement. Go to Create subhead and click on Parameter > New Custom Parameter. Change the name to "Distance" and the default value to 0.2, minimum to 0 and
maximum to 3. In the expression editor change the equation to “Fc * SoccerBall.power.distance”. Now, validate and apply the equation again. You would have 3 value sliders to control the
animation of the ball. Change around with the values to get your desired animation. Now play the animation and drag the sliders to get the animation you want

To see your animation and save it as a video clip, go to the Render toolbar and under render select All passes, your
animation would be rendered and saved in the set project folder.

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