uniform float sizeScalar;
varying float particleID;
varying vec4 particleColor;
varying vec2 textureOffset;
varying float textureDiv;

#define SPRITE_TILING	4.0			// set this to the tilling factor in the sprite texture
#define SPRITE_DIV 1.0 / SPRITE_TILING		

void main(void) 
{
	// The ICE graph defines the radius of each particle
	// and the hardware mapping widget on the "advanced"
	// tab stores the value of the radius attribute in the 
	// R component of the color (see advanced tab).
	gl_PointSize = gl_SecondaryColor.g * sizeScalar;

	// pass the color of the particle to the fragment shader
	particleColor = gl_Color;

	// pass the ID of the particle to the fragment shader, this
	// will be used to generate texture coordinate into the 
	// texture to select the right sprite image
	particleID = gl_SecondaryColor.r;

	textureOffset.x = SPRITE_DIV * mod(particleID,SPRITE_TILING);
	textureOffset.y = SPRITE_DIV * floor(SPRITE_TILING*SPRITE_TILING/particleID);
	textureDiv = SPRITE_DIV;

	// transform particle
	gl_Position = ftransform();
}