uniform float CurrentTime;
uniform float MaxTime;

const vec4 Gravity = vec4(0.0, -4.4, 0.0, 0.0);

void main()
{
    vec4 velocity = vec4(0.0, 0.0, 0.0, 1.0);
    vec4 position = vec4(0.0, 0.0, 0.0, 1.0);

    velocity.x = gl_Vertex.x; 
    velocity.y = gl_Vertex.y + Gravity.y*CurrentTime*0.001;
    velocity.z = gl_Vertex.z;
    position.x = velocity.x*CurrentTime*0.001;
    position.y = velocity.y*CurrentTime*0.001;
    position.z = velocity.z*CurrentTime*0.001;

    gl_Position   = gl_ModelViewProjectionMatrix*position;
    gl_FrontColor = gl_Color;
    gl_PointSize  = 4.0 - 3.9*CurrentTime/MaxTime;
}