103 lines
4.8 KiB
Plaintext
103 lines
4.8 KiB
Plaintext
/****************************************************************************
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**
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** Copyright (C) 2016 The Qt Company Ltd.
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** Contact: https://www.qt.io/licensing/
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**
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** This file is part of the documentation of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:FDL$
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** Commercial License Usage
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** Licensees holding valid commercial Qt licenses may use this file in
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** accordance with the commercial license agreement provided with the
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** Software or, alternatively, in accordance with the terms contained in
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** a written agreement between you and The Qt Company. For licensing terms
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** and conditions see https://www.qt.io/terms-conditions. For further
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** information use the contact form at https://www.qt.io/contact-us.
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**
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** GNU Free Documentation License Usage
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** Alternatively, this file may be used under the terms of the GNU Free
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** Documentation License version 1.3 as published by the Free Software
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** Foundation and appearing in the file included in the packaging of
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** this file. Please review the following information to ensure
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** the GNU Free Documentation License version 1.3 requirements
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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/*!
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\example animation/stickman
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\title Stickman Example
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\brief The Stickman example shows how to animate transitions in a state
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machine to implement key frame animations.
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\image stickman-example.png
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In this example, we will write a small application which animates the joints in a skeleton and
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projects a stickman figure on top. The stickman can be either "alive" or "dead", and when in the
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"alive" state, he can be performing different actions defined by key frame animations.
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Animations are implemented as composite states. Each child state of the animation state
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represents a frame in the animation by setting the position of each joint in the stickman's
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skeleton to the positions defined for the particular frame. The frames are then bound together
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with animated transitions that trigger on the source state's propertiesAssigned() signal. Thus,
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the machine will enter the state representing the next frame in the animation immediately after
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it has finished animating into the previous frame.
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\image stickman-example1.png
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The states for an animation is constructed by reading a custom animation file format and
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creating states that assign values to the "position" properties of each of the nodes in the
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skeleton graph.
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\snippet animation/stickman/lifecycle.cpp 1
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The states are then bound together with signal transitions that listen to the
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propertiesAssigned() signal.
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\snippet animation/stickman/lifecycle.cpp 2
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The last frame state is given a transition to the first one, so that the animation will loop
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until it is interrupted when a transition out from the animation state is taken. To get smooth
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animations between the different key frames, we set a default animation on the state machine.
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This is a parallel animation group which contains animations for all the "position" properties
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and will be selected by default when taking any transition that leads into a state that assigns
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values to these properties.
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\snippet animation/stickman/lifecycle.cpp 3
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Several such animation states are constructed, and are placed together as children of a top
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level "alive" state which represents the stickman life cycle. Transitions go from the parent
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state to the child state to ensure that each of the child states inherit them.
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\image stickman-example2.png
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This saves us the effort of connect every state to every state with identical transitions. The
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state machine makes sure that transitions between the key frame animations are also smooth by
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applying the default animation when interrupting one and starting another.
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Finally, there is a transition out from the "alive" state and into the "dead" state. This is
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a custom transition type called LightningSrikesTransition which samples every second and
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triggers at random (one out of fifty times on average.)
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\snippet animation/stickman/lifecycle.cpp 4
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When it triggers, the machine will first enter a "lightningBlink" state which uses a timer to
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pause for a brief period of time while the background color of the scene is white. This gives us
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a flash effect when the lightning strikes.
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\snippet animation/stickman/lifecycle.cpp 5
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We start and stop a QTimer object when entering and exiting the state. Then we transition into
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the "dead" state when the timer times out.
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\snippet animation/stickman/lifecycle.cpp 0
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When the machine is in the "dead" state, it will be unresponsive. This is because the "dead"
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state has no transitions leading out.
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\image stickman-example3.png
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*/
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