Qt provides us with several different sub-systems to create animations for our GUI, including timer, timeline, animation framework, state machine framework, and graphics view framework:

• Timer: Qt provides us with repetitive and single-shot timers. When the timeout value is reached, an event callback function will be triggered through Qt's signal-and-slot mechanism. You can make use of a timer to change the properties (color, position, scale, and so on) of your GUI element within a given interval to create an animation.
• Timeline: Timeline calls a slot periodically to animate a GUI element. It is quite similar to a repetitive timer, but instead of doing the same thing all of the time when the slot is triggered, timeline provides a value to the slot to indicate its current frame index so that you can do different things (such as offset to a different space of the sprite sheet) based on the given value.
• Animation framework: The animation framework makes animating a GUI element easy by allowing its properties to be animated. The animations are controlled by using easing curves. Easing curves describe a function that controls what the speed of the animation should be, resulting in different acceleration and deceleration patterns. The types of easing curve supported by Qt include linear, quadratic, cubic, quartic, sine, exponential, circular, and elastic.
• State machine framework: Qt provides us with classes for creating and executing state graphs, which allow each GUI element to move from one state to another when triggered by signals. The state graph in the state machine framework is hierarchical, which means every state can also be nested inside of other states.
• Graphics view framework: The graphics view framework is a powerful graphics engine for visualizing and interacting with a large number of custom-made 2D graphical items. You can use the graphics view framework to draw your GUI and have them animated in a totally manual way if you are an experienced programmer.

By making use of all of the powerful features we've mentioned here, we're able to create an intuitive and modern GUI with ease. In this chapter, we will look into the practical approaches to animating GUI elements using Qt.