Tips & Techniques 4 Visible and Invisible Objects

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Tips & Techniques 4 Visible and Invisible Objects. Alice. Opacity. Opacity is a measure of how "see-through" an image or an object is. The less opaque an object is, the more see-through it is. Opacity of 100%, cannot see through the object

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Tips & Techniques 4Visible and Invisible Objects

Alice

Opacity
• Opacity is a measure of how "see-through" an image or an object is.
• The less opaque an object is, the more see-through it is.
• Opacity of 100%, cannot see through the object
• Opacity of 0%, object is transparent (like clear glass)
• In Alice, an object with an opacity of 0% is invisible.
Changing the Opacity
• A change in opacity can be used to simulate real world conditions.
• Example
• A fish swimming away from the camera should fade away because water blurs our vision of distant objects.
Demo
• Ch04Lec4LilfishOpacity
• Concepts illustrated in this example
• As opacity is gradually decreased, the fish becomes less visible.
• At an opacity of 0%, the object is still in the world (can still see it listed in the object tree) but is effectively invisible.
isShowing
• The isShowing property has a Boolean value, either true or false.
• Setting an object's isShowing property to false makes the object invisible in the world.
• Once again, the object is not removed from the world, it is simply not visible in the world.
Demo
• Ch04Lec4ChickenIsShowing
• Concepts illustrated in this example
• A billboard can be used to display a title screen for the animation.
• A 2-second wait gives the user time to read the billboard.
• Changing the isShowing property to false makes the title screen disappear.
Two properties
• isShowing and opacity are two different properties.
• isShowing works like an on/off switch
• opacity works like a dimmer switch
• Although each can be used to make an object invisible, changing one does not automatically change the value of the other!
Practical Uses of Invisible Objects
• An invisible object is sometimes useful as a stationary marker that creates
• a target for a move to instruction
• an external reference point for object rotational motion
Demos
• Ch04Lec4InvisibleTarget
• Invisible circle makes it possible to move the object to a landing target.
• Ch04Lec4InvisibleReferencePoint
• External reference point acts as a pivot for the rotational movement of each object.