layout(lines, invocations=2) in;
layout(triangle_strip, max_vertices=8) out;
out vec4 fcolor;
in vec4 fca[];
uniform mat4 mvp;
uniform float fruitdrop;
uniform float wind;
in int gl_InvocationID;

void emitsimple(vec4 position){
	gl_Position = mvp * position;
	fcolor = fca[0];
	EmitVertex();
}

void emitpanel(vec4 start, vec4 end, vec4 addition){
	emitsimple(start + addition);
	emitsimple(start - addition);
	emitsimple(end + addition);
	emitsimple(end - addition);
	EndPrimitive();

}

void branch(vec4 start, vec4 end){ // Maybe number of sides as a parameter
	float thickness = distance(start, end) / 10.0;
	emitpanel(start, end, vec4(thickness, 0, 0, 0));	
	emitpanel(start, end, vec4(0, 0, thickness, 0));	
}

void fvemit(vec4 pos){
	gl_Position = mvp * (pos + vec4(0, -min(fruitdrop, pos.y + 2), 0, 0));
	fcolor = vec4(1, 0, 0, 1);
	EmitVertex();
}

void makefruit(vec4 spot, float size){
	vec4 a = spot + vec4(-size, -size, -size, 0);
	vec4 b = spot + vec4(size, -size, -size, 0);
	vec4 c = spot + vec4(0, -size, size, 0);
	vec4 d = spot + vec4(0, size, 0, 0);
	fvemit(a);
	fvemit(b);
	fvemit(c);
	fvemit(d);
	fvemit(b);
	fvemit(a);
}

void main(){
	vec4 start = gl_in[0].gl_Position;
	vec4 end = gl_in[1].gl_Position;

	if(gl_InvocationID == 0 || fruitdrop == 0.0){
		if(start.y > -2)
			start.x += (start.y + 2) / 5.0 * wind;
		if(end.y > -2)
			end.x += (end.y + 2) / 5.0 * wind;
	}
	
	if(gl_InvocationID == 0){
		branch(start, end);	
	} else if(gl_InvocationID == 1) {
		if(distance(start, end) < .1){
			makefruit(end, .05);
		}
	}
}