Swinging geometry shader for structure

swing.glsl

attribute vec4 vertex;
attribute vec4 normal;
attribute vec2 textureCoord;
varying vec4 ncoord;
varying vec4 vcoord;

varying vec2 tcoord;			// 
uniform sampler2D tex;			// texture one
uniform sampler2D tex2;			// texture two
uniform vec2 tres;			// size of texture (screen)
uniform vec4 fparams;			// 4 floats coming in 
uniform float ftime;			// 0.0 to 1.0
uniform int itime;			// increases when ftime hits 1.0

uniform mat4 MVP;
//f1:swing amount:

#define PI 3.1415926535897932384626
float time = float(itime) + ftime;

// https://github.com/dmnsgn/glsl-rotate/blob/master/rotation-3d-y.glsl
mat4 rotation3dY(float angle) {
	float s = sin(angle);
	float c = cos(angle);

	return mat4(
		  c,  0.0,   -s,  0.0,
		0.0,  1.0,  0.0,  0.0,
		  s,  0.0,    c,  0.0,
    0.0,  0.0,  0.0,  1.0
	);
}

void main(void) 
{
  vec4  c   = texture2D(tex2,textureCoord);
  tcoord = textureCoord;

  // my demo code
  // vec4 vertex = a_position;

  vec4 v = vertex;

  v = v * rotation3dY(sin(time + v.y) * fparams[1]);

  vec4 Vert = MVP * v;

  ncoord = normal;
  gl_Position = Vert;
}