backIn backInOut backOut bounceIn bounceInOut bounceOut byName circularIn circularInOut circularOut cubicIn cubicInOut cubicOut def elasticIn elasticInOut elasticOut exponentialIn exponentialInOut exponentialOut linear quadraticIn quadraticInOut quadraticOut quarticIn quarticInOut quarticOut quinticIn quinticInOut quinticOut sinusoidalIn sinusoidalInOut sinusoidalOut stepped

linear detail::linearEasing linear {} inlineconstexpr Linear easing function with constant velocity throughout the animation. The linear easing function produces uniform motion with no acceleration or deceleration. The interpolation progresses at a constant rate from start to finish, creating mechanical, predictable movement. Linear easing is characterized by: Constant velocity: the rate of change never varies No ease-in or ease-out: motion starts and stops abruptly Simple mathematical relationship: output = start + (end - start) * progress Predictable timing: halfway through time means halfway through distance This easing is appropriate for: Mechanical objects: Conveyor belts, pistons, automated systems Progress indicators: Loading bars, timers, countdowns Continuous loops: Rotating objects, scrolling backgrounds Data visualization: Graph animations where consistency is important Debug and testing: Predictable behavior for verification Linear easing is generally not recommended for most UI animations because: Lacks the natural feel of acceleration/deceleration Abrupt starts and stops can feel jarring Missing visual polish that easing provides Human perception expects objects to ease into and out of motion However, it serves as the foundation for all other easing functions and is essential when mechanical precision is more important than natural motion feel. Mathematically, this implements: f(t) = t where t is normalized progress [0, 1]. // Constant velocity scrolling background auto scroll = tweeny::from(0.0f) .to(1000.0f) .via(easing::linear) .during(600U) .build(); // Progress indicator that matches time exactly auto progress = tweeny::from(0) .to(100) .via(easing::linear) .during(100U) .build(); // At frame 50, progress will be exactly 50 Note Linear is the default easing when no via() is specified, though using def is more explicit in code. See also def Alias for linear easing quadraticInOut For a gentle alternative with ease-in and ease-out sinusoidalInOut For smooth, natural-feeling motion