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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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37 ** |
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38 ** $QT_END_LICENSE$ |
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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \example animation/stickman |
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44 \title Stickman Example |
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45 |
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46 The Stickman example shows how to animate transitions in a state machine to implement key frame |
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47 animations. |
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48 |
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49 \image stickman-example.png |
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50 |
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51 In this example, we will write a small application which animates the joints in a skeleton and |
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52 projects a stickman figure on top. The stickman can be either "alive" or "dead", and when in the |
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53 "alive" state, he can be performing different actions defined by key frame animations. |
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54 |
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55 Animations are implemented as composite states. Each child state of the animation state |
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56 represents a frame in the animation by setting the position of each joint in the stickman's |
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57 skeleton to the positions defined for the particular frame. The frames are then bound together |
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58 with animated transitions that trigger on the source state's propertiesAssigned() signal. Thus, |
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59 the machine will enter the state representing the next frame in the animation immediately after |
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60 it has finished animating into the previous frame. |
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61 |
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62 \image stickman-example1.png |
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63 |
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64 The states for an animation is constructed by reading a custom animation file format and |
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65 creating states that assign values to the the "position" properties of each of the nodes in the |
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66 skeleton graph. |
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67 |
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68 \snippet examples/animation/stickman/lifecycle.cpp 1 |
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69 |
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70 The states are then bound together with signal transitions that listen to the |
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71 propertiesAssigned() signal. |
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72 |
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73 \snippet examples/animation/stickman/lifecycle.cpp 2 |
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74 |
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75 The last frame state is given a transition to the first one, so that the animation will loop |
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76 until it is interrupted when a transition out from the animation state is taken. To get smooth |
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77 animations between the different key frames, we set a default animation on the state machine. |
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78 This is a parallel animation group which contains animations for all the "position" properties |
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79 and will be selected by default when taking any transition that leads into a state that assigns |
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80 values to these properties. |
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81 |
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82 \snippet examples/animation/stickman/lifecycle.cpp 3 |
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83 |
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84 Several such animation states are constructed, and are placed together as children of a top |
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85 level "alive" state which represents the stickman life cycle. Transitions go from the parent |
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86 state to the child state to ensure that each of the child states inherit them. |
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87 |
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88 \image stickman-example2.png |
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89 |
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90 This saves us the effort of connect every state to every state with identical transitions. The |
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91 state machine makes sure that transitions between the key frame animations are also smooth by |
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92 applying the default animation when interrupting one and starting another. |
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93 |
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94 Finally, there is a transition out from the "alive" state and into the "dead" state. This is |
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95 a custom transition type called LightningSrikesTransition which samples every second and |
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96 triggers at random (one out of fifty times on average.) |
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97 |
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98 \snippet examples/animation/stickman/lifecycle.cpp 4 |
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99 |
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100 When it triggers, the machine will first enter a "lightningBlink" state which uses a timer to |
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101 pause for a brief period of time while the background color of the scene is white. This gives us |
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102 a flash effect when the lightning strikes. |
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103 |
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104 \snippet examples/animation/stickman/lifecycle.cpp 5 |
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105 |
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106 We start and stop a QTimer object when entering and exiting the state. Then we transition into |
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107 the "dead" state when the timer times out. |
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108 |
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109 \snippet examples/animation/stickman/lifecycle.cpp 0 |
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110 |
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111 When the machine is in the "dead" state, it will be unresponsive. This is because the "dead" |
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112 state has no transitions leading out. |
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113 |
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114 \image stickman-example3.png |
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115 |
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116 */ |