What is Smoothie?
Smoothie is a C++ implementation of a physical simulation engine for GUI animations. It calculates the current (per frame) position of a UI element by it’s final position.
What is Smoothie good for (features) ?
- Animations are smooth, velocity does not change abruptly, feels natural & easy for the eye to track.
- Animations are parametric yet simple, only a final position is needed to start an animation.
- Final position may be changed during an ongoing animation.
- Animation time can be limited, a distant final position doesn’t mean a long animation.
- Animations can be started by a drag & release action, resulting animation may be constrained.
- Low CPU usage, works on mobile devices.
- OS independent.
- Open source (MIT license)
Usage
Setup
The following code will be used in all the examples.
#include "Smoothie.h"
// this function simulates 25 fps
unsigned int simulator25fps(void)
{
static unsigned int ticks = 0;
ticks += 40;
return ticks;
}
// assign an implementation
Smoothie::getTimeMsecFuncPtr Smoothie::getTimeMsec = simulator25fps;
// print x space marks followed by an asterisk
void show(int x)
{
while(x--)
printf(" ");
printf("*\n");
}
In the following examples I will use a smoothie as defined below:
// create a smoothie positioned at 0, that traverses a distance of 180 win 2000ms (=2 seconds) Smoothie smoothie(0, 180, 2000);
Requesting an animation of a distance less than 180, will take less that 2000ms.
Requesting an animation of a distance greater than 180, will cause the smoothie to skip the section with the highest speed, so that the total time of the animation will be 2000ms.
Example 1: Going from 0 to 120
// start animation
smoothie.setFinalPosition(120);
unsigned int timeTillIdle;
do
{
// calculate current position
int x = smoothie.calcCurrentPosition(&timeTillIdle);
show(x); // show on the screen the value of x
} while(timeTillIdle); // stop when smoothie is idle: timeTillIdle==0
Example 2: Going from 0 to 120, aborting at 60
// start animation
smoothie.setFinalPosition(120);
unsigned int timeTillIdle;
do
{
// calculate current position
int x = smoothie.calcCurrentPosition(&timeTillIdle);
// request to go back to 0 if we reached 60
if(x >= 60 && smoothie.getFinalPosition() == 120)
smoothie.setFinalPosition(0);
show(x); // show on the screen the value of x
} while(timeTillIdle); // stop when smoothie is idle: timeTillIdle==0
Example 3: “glide” animation after a drag-release action
// drag was released at position=0 with velocity=500.
// final position is in the range of [50..120], bounce size is 20
smoothie.setCurrentConstraint(0, 500, 50, 120, 20);
unsigned int timeTillIdle;
do
{
// calculate current position
int x = smoothie.calcCurrentPosition(&timeTillIdle);
show(x); // show on the screen the value of x
} while(timeTillIdle); // stop when smoothie is idle: timeTillIdle==0
