attribute vec4 a_CornerTextureCoordinate;
attribute vec3 a_Position;
attribute vec3 a_Velocity;
attribute vec4 a_Color;
attribute vec3 a_SizeRotation;
attribute vec4 a_RadiusRadian;
attribute float a_AgeAddScale;
attribute float a_Time;

varying vec4 v_Color;
varying vec2 v_TextureCoordinate;

uniform  float u_CurrentTime;
uniform float u_Duration;
uniform float u_EndVelocity;
uniform vec3 u_Gravity;

#ifdef PARTICLE3D
 uniform mat4 u_WorldMat;
 uniform mat4 u_View;
 uniform mat4 u_Projection;
 uniform vec2 u_ViewportScale;
#else
 uniform vec2 size;
 uniform mat4 mmat;
#endif

vec4 ComputeParticlePosition(in vec3 position, in vec3 velocity,in float age,in float normalizedAge)
{

   float startVelocity = length(velocity);//起始标量速度
   float endVelocity = startVelocity * u_EndVelocity;//结束标量速度

   float velocityIntegral = startVelocity * normalizedAge +(endVelocity - startVelocity) * normalizedAge *normalizedAge/2.0;//计算当前速度的标量（单位空间），vt=v0*t+(1/2)*a*(t^2)
   
   vec3 addPosition = normalize(velocity) * velocityIntegral * u_Duration;//计算受自身速度影响的位置，转换标量到矢量    
   addPosition += u_Gravity * age * normalizedAge;//计算受重力影响的位置
   
   float radius=mix(a_RadiusRadian.x, a_RadiusRadian.y, normalizedAge); //计算粒子受半径和角度影响（无需计算角度和半径时，可用宏定义优化屏蔽此计算）
   float radianHorizontal =a_RadiusRadian.z*normalizedAge;
   float radianVertical =a_RadiusRadian.w*normalizedAge;
   
   float r =cos(radianVertical)* radius;
   addPosition.y += sin(radianVertical) * radius;
	
   addPosition.x += cos(radianHorizontal) *r;
   addPosition.z += sin(radianHorizontal) *r;
  
   #ifdef PARTICLE3D
   position+=addPosition;
    return  u_Projection*u_View*u_WorldMat*(vec4(position, 1.0));
   #else
   addPosition.y=-addPosition.y;//2D粒子位置更新需要取负，2D粒子坐标系Y轴正向朝上
   position+=addPosition;
    return vec4(position.xy,0.0,1.0);
   #endif
}

float ComputeParticleSize(in float startSize,in float endSize, in float normalizedAge)
{    
    float size = mix(startSize, endSize, normalizedAge);
    
	#ifdef PARTICLE3D
    //Project the size into screen coordinates.
     return size * u_Projection[1][1];
	#else
	 return size;
	#endif
}

mat2 ComputeParticleRotation(in float rot,in float age)
{    
    float rotation =rot * age;
    //计算2x2旋转矩阵.
    float c = cos(rotation);
    float s = sin(rotation);
    return mat2(c, -s, s, c);
}

vec4 ComputeParticleColor(in vec4 color,in float normalizedAge)
{
    //硬编码设置，使粒子淡入很快，淡出很慢,6.7的缩放因子把置归一在0到1之间，可以谷歌x*(1-x)*(1-x)*6.7的制图表
    color.a *= normalizedAge * (1.0-normalizedAge) * (1.0-normalizedAge) * 6.7;
   
    return color;
}

void main()
{
   float age = u_CurrentTime - a_Time;
   age *= 1.0 + a_AgeAddScale;
   float normalizedAge = clamp(age / u_Duration,0.0,1.0);
   gl_Position = ComputeParticlePosition(a_Position, a_Velocity, age, normalizedAge);//计算粒子位置
   float pSize = ComputeParticleSize(a_SizeRotation.x,a_SizeRotation.y, normalizedAge);
   mat2 rotation = ComputeParticleRotation(a_SizeRotation.z, age);
	
   #ifdef PARTICLE3D
	gl_Position.xy += (rotation*a_CornerTextureCoordinate.xy) * pSize * u_ViewportScale;
   #else
	gl_Position.xy += (rotation*a_CornerTextureCoordinate.xy) * pSize;
    gl_Position=vec4((gl_Position.x/size.x-0.5)*2.0,(0.5-gl_Position.y/size.y)*2.0,0.0,1.0);
   #endif
   
   v_Color = ComputeParticleColor(a_Color, normalizedAge);
   v_TextureCoordinate =a_CornerTextureCoordinate.zw;
}