unity中的缓动插值曲线，Easing Curves的那些事

这个地址是一个可以查看各种插值效果的 flash demo
http://robertpenner.com/easing/easing_demo.html

现在浏览器都不支持flash插件了，补个图吧

在 unity 中做 ease 操作最好的选择，当然是使用 dotween 插件了。
不过总有某些情景下，是不能借助这些现成工具的，这个时候，怎么自己实现这些效果呢？
其实还是可以从 dotween 上想办法的，这里顺便教大家一个小方法，就是先下载 dotween 的源代码。然后在里面进行全局搜索，如下图所示：

有一个 “Easing Curves” 的 region 块，这个块里放的就是所有 dotween 里支持的所有曲线计算公式了。
这里为了大家省事，我把它们都给贴出来，自取吧。

#region Easing Curves
	
	private float linear(float start, float end, float value){
		return Mathf.Lerp(start, end, value);
	}
	
	private float clerp(float start, float end, float value){
		float min = 0.0f;
		float max = 360.0f;
		float half = Mathf.Abs((max - min) * 0.5f);
		float retval = 0.0f;
		float diff = 0.0f;
		if ((end - start) < -half){
			diff = ((max - start) + end) * value;
			retval = start + diff;
		}else if ((end - start) > half){
			diff = -((max - end) + start) * value;
			retval = start + diff;
		}else retval = start + (end - start) * value;
		return retval;
    }

	private float spring(float start, float end, float value){
		value = Mathf.Clamp01(value);
		value = (Mathf.Sin(value * Mathf.PI * (0.2f + 2.5f * value * value * value)) * Mathf.Pow(1f - value, 2.2f) + value) * (1f + (1.2f * (1f - value)));
		return start + (end - start) * value;
	}

	private float easeInQuad(float start, float end, float value){
		end -= start;
		return end * value * value + start;
	}

	private float easeOutQuad(float start, float end, float value){
		end -= start;
		return -end * value * (value - 2) + start;
	}

	private float easeInOutQuad(float start, float end, float value){
		value /= .5f;
		end -= start;
		if (value < 1) return end * 0.5f * value * value + start;
		value--;
		return -end * 0.5f * (value * (value - 2) - 1) + start;
	}

	private float easeInCubic(float start, float end, float value){
		end -= start;
		return end * value * value * value + start;
	}

	private float easeOutCubic(float start, float end, float value){
		value--;
		end -= start;
		return end * (value * value * value + 1) + start;
	}

	private float easeInOutCubic(float start, float end, float value){
		value /= .5f;
		end -= start;
		if (value < 1) return end * 0.5f * value * value * value + start;
		value -= 2;
		return end * 0.5f * (value * value * value + 2) + start;
	}

	private float easeInQuart(float start, float end, float value){
		end -= start;
		return end * value * value * value * value + start;
	}

	private float easeOutQuart(float start, float end, float value){
		value--;
		end -= start;
		return -end * (value * value * value * value - 1) + start;
	}

	private float easeInOutQuart(float start, float end, float value){
		value /= .5f;
		end -= start;
		if (value < 1) return end * 0.5f * value * value * value * value + start;
		value -= 2;
		return -end * 0.5f * (value * value * value * value - 2) + start;
	}

	private float easeInQuint(float start, float end, float value){
		end -= start;
		return end * value * value * value * value * value + start;
	}

	private float easeOutQuint(float start, float end, float value){
		value--;
		end -= start;
		return end * (value * value * value * value * value + 1) + start;
	}

	private float easeInOutQuint(float start, float end, float value){
		value /= .5f;
		end -= start;
		if (value < 1) return end * 0.5f * value * value * value * value * value + start;
		value -= 2;
		return end * 0.5f * (value * value * value * value * value + 2) + start;
	}

	private float easeInSine(float start, float end, float value){
		end -= start;
		return -end * Mathf.Cos(value * (Mathf.PI * 0.5f)) + end + start;
	}

	private float easeOutSine(float start, float end, float value){
		end -= start;
		return end * Mathf.Sin(value * (Mathf.PI * 0.5f)) + start;
	}

	private float easeInOutSine(float start, float end, float value){
		end -= start;
		return -end * 0.5f * (Mathf.Cos(Mathf.PI * value) - 1) + start;
	}

	private float easeInExpo(float start, float end, float value){
		end -= start;
		return end * Mathf.Pow(2, 10 * (value - 1)) + start;
	}

	private float easeOutExpo(float start, float end, float value){
		end -= start;
		return end * (-Mathf.Pow(2, -10 * value ) + 1) + start;
	}

	private float easeInOutExpo(float start, float end, float value){
		value /= .5f;
		end -= start;
		if (value < 1) return end * 0.5f * Mathf.Pow(2, 10 * (value - 1)) + start;
		value--;
		return end * 0.5f * (-Mathf.Pow(2, -10 * value) + 2) + start;
	}

	private float easeInCirc(float start, float end, float value){
		end -= start;
		return -end * (Mathf.Sqrt(1 - value * value) - 1) + start;
	}

	private float easeOutCirc(float start, float end, float value){
		value--;
		end -= start;
		return end * Mathf.Sqrt(1 - value * value) + start;
	}

	private float easeInOutCirc(float start, float end, float value){
		value /= .5f;
		end -= start;
		if (value < 1) return -end * 0.5f * (Mathf.Sqrt(1 - value * value) - 1) + start;
		value -= 2;
		return end * 0.5f * (Mathf.Sqrt(1 - value * value) + 1) + start;
	}

	/* GFX47 MOD START */
	private float easeInBounce(float start, float end, float value){
		end -= start;
		float d = 1f;
		return end - easeOutBounce(0, end, d-value) + start;
	}
	/* GFX47 MOD END */

	/* GFX47 MOD START */
	//private float bounce(float start, float end, float value){
	private float easeOutBounce(float start, float end, float value){
		value /= 1f;
		end -= start;
		if (value < (1 / 2.75f)){
			return end * (7.5625f * value * value) + start;
		}else if (value < (2 / 2.75f)){
			value -= (1.5f / 2.75f);
			return end * (7.5625f * (value) * value + .75f) + start;
		}else if (value < (2.5 / 2.75)){
			value -= (2.25f / 2.75f);
			return end * (7.5625f * (value) * value + .9375f) + start;
		}else{
			value -= (2.625f / 2.75f);
			return end * (7.5625f * (value) * value + .984375f) + start;
		}
	}
	/* GFX47 MOD END */

	/* GFX47 MOD START */
	private float easeInOutBounce(float start, float end, float value){
		end -= start;
		float d = 1f;
		if (value < d* 0.5f) return easeInBounce(0, end, value*2) * 0.5f + start;
		else return easeOutBounce(0, end, value*2-d) * 0.5f + end*0.5f + start;
	}
	/* GFX47 MOD END */

	private float easeInBack(float start, float end, float value){
		end -= start;
		value /= 1;
		float s = 1.70158f;
		return end * (value) * value * ((s + 1) * value - s) + start;
	}

	private float easeOutBack(float start, float end, float value){
		float s = 1.70158f;
		end -= start;
		value = (value) - 1;
		return end * ((value) * value * ((s + 1) * value + s) + 1) + start;
	}

	private float easeInOutBack(float start, float end, float value){
		float s = 1.70158f;
		end -= start;
		value /= .5f;
		if ((value) < 1){
			s *= (1.525f);
			return end * 0.5f * (value * value * (((s) + 1) * value - s)) + start;
		}
		value -= 2;
		s *= (1.525f);
		return end * 0.5f * ((value) * value * (((s) + 1) * value + s) + 2) + start;
	}

	private float punch(float amplitude, float value){
		float s = 9;
		if (value == 0){
			return 0;
		}
		else if (value == 1){
			return 0;
		}
		float period = 1 * 0.3f;
		s = period / (2 * Mathf.PI) * Mathf.Asin(0);
		return (amplitude * Mathf.Pow(2, -10 * value) * Mathf.Sin((value * 1 - s) * (2 * Mathf.PI) / period));
    }
	
	/* GFX47 MOD START */
	private float easeInElastic(float start, float end, float value){
		end -= start;
		
		float d = 1f;
		float p = d * .3f;
		float s = 0;
		float a = 0;
		
		if (value == 0) return start;
		
		if ((value /= d) == 1) return start + end;
		
		if (a == 0f || a < Mathf.Abs(end)){
			a = end;
			s = p / 4;
			}else{
			s = p / (2 * Mathf.PI) * Mathf.Asin(end / a);
		}
		
		return -(a * Mathf.Pow(2, 10 * (value-=1)) * Mathf.Sin((value * d - s) * (2 * Mathf.PI) / p)) + start;
	}		
	/* GFX47 MOD END */

	/* GFX47 MOD START */
	//private float elastic(float start, float end, float value){
	private float easeOutElastic(float start, float end, float value){
	/* GFX47 MOD END */
		//Thank you to rafael.marteleto for fixing this as a port over from Pedro's UnityTween
		end -= start;
		
		float d = 1f;
		float p = d * .3f;
		float s = 0;
		float a = 0;
		
		if (value == 0) return start;
		
		if ((value /= d) == 1) return start + end;
		
		if (a == 0f || a < Mathf.Abs(end)){
			a = end;
			s = p * 0.25f;
			}else{
			s = p / (2 * Mathf.PI) * Mathf.Asin(end / a);
		}
		
		return (a * Mathf.Pow(2, -10 * value) * Mathf.Sin((value * d - s) * (2 * Mathf.PI) / p) + end + start);
	}		
	
	/* GFX47 MOD START */
	private float easeInOutElastic(float start, float end, float value){
		end -= start;
		
		float d = 1f;
		float p = d * .3f;
		float s = 0;
		float a = 0;
		
		if (value == 0) return start;
		
		if ((value /= d*0.5f) == 2) return start + end;
		
		if (a == 0f || a < Mathf.Abs(end)){
			a = end;
			s = p / 4;
			}else{
			s = p / (2 * Mathf.PI) * Mathf.Asin(end / a);
		}
		
		if (value < 1) return -0.5f * (a * Mathf.Pow(2, 10 * (value-=1)) * Mathf.Sin((value * d - s) * (2 * Mathf.PI) / p)) + start;
		return a * Mathf.Pow(2, -10 * (value-=1)) * Mathf.Sin((value * d - s) * (2 * Mathf.PI) / p) * 0.5f + end + start;
	}		
	/* GFX47 MOD END */
	
	#endregion	
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