layout (triangles) in;
layout (triangle_strip, max_vertices = 3) out;

vec2 aViewRes = vec2(400.0, 400.0);
vec2 aViewOffset = vec2(0.0, 0.0);
mat4 aMat = occProjectionMatrix * occWorldViewMatrix * occModelWorldMatrix;

vec3 toWinCoord(vec3 theVec)
{
	vec4 aTransCoord = aMat * vec4(theVec, 1.0);
	vec3 aWinCoord = aTransCoord.xyz / aTransCoord.w;
	aWinCoord = aWinCoord * 0.5 + 0.5;
	aWinCoord.x = aWinCoord.x * aViewRes.x + aViewOffset.x;
	aWinCoord.y = aWinCoord.y * aViewRes.y + aViewOffset.y;
	return aWinCoord;
}

vec3 toObjectCoord(vec3 theVec)
{
	theVec.x = (theVec.x - aViewOffset.x) / aViewRes.x;
	theVec.y = (theVec.y - aViewOffset.y) / aViewRes.y;
	theVec = theVec * 2.0 - 1.0;
	vec4 aObjectCoord = inverse(aMat) * vec4(theVec, 1.0);
	aObjectCoord.xyz /= aObjectCoord.w;
	return aObjectCoord.xyz;
}

void shrinkTriangle(float theValue)
{
	vec3 aWinCoordCenter = toWinCoord(vec3(0.0, 0.0, 0.0));
	aWinCoordCenter.xy += theValue;
	float aShift = length(toObjectCoord(aWinCoordCenter)); 
	//aShift = aShift - theValue * 0.075; //for triangles
	//aShift = aShift - theValue * 0.0038; //for box
	for (int aTriVertIter = 0; aTriVertIter < 3; ++aTriVertIter) 
	{
		vec3 aLeftPoint = gl_in[aTriVertIter].gl_Position.xyz;
		vec3 aRightPoint = gl_in[aTriVertIter].gl_Position.xyz;
		for(int i = 0; i < gl_in.length(); i++)
		{
			if(gl_in[i].gl_Position.xyz == gl_in[aTriVertIter].gl_Position.xyz)
			{
				continue;
			}
			else
			{
				if (aLeftPoint == gl_in[aTriVertIter].gl_Position.xyz)
				{
					aLeftPoint = gl_in[i].gl_Position.xyz;
					continue;
				}
				if (aRightPoint == gl_in[aTriVertIter].gl_Position.xyz)
				{
					aRightPoint = gl_in[i].gl_Position.xyz;
					continue;
				}
			}
		}
		vec3 aLeftVec = aLeftPoint - gl_in[aTriVertIter].gl_Position.xyz;
		vec3 aRightVec = aRightPoint - gl_in[aTriVertIter].gl_Position.xyz;
		float aAngle = acos(dot(aLeftVec, aRightVec) / (length(aLeftVec) * length(aRightVec)));
		float aScaleFactor = aShift / sin(aAngle / 2.0);
		vec3 aMoveVec = normalize(normalize(aLeftVec) + normalize(aRightVec));
		vec3 aVertRes = gl_in[aTriVertIter].gl_Position.xyz + aMoveVec * aScaleFactor;
		gl_Position = aMat * vec4 (aVertRes, 1.0);
		EmitVertex();
	}
}

void shrinkTrianglePix(float theValue)
{
	for (int aTriVertIter = 0; aTriVertIter < 3; ++aTriVertIter) 
	{
		vec3 aLeftPoint = toWinCoord(gl_in[aTriVertIter].gl_Position.xyz);
		vec3 aRightPoint = toWinCoord(gl_in[aTriVertIter].gl_Position.xyz);
		for(int i = 0; i < gl_in.length(); i++)
		{
			if(toWinCoord(gl_in[i].gl_Position.xyz) == toWinCoord(gl_in[aTriVertIter].gl_Position.xyz))
			{
				continue;
			}
			else
			{
				if (aLeftPoint == toWinCoord(gl_in[aTriVertIter].gl_Position.xyz))
				{
					aLeftPoint = toWinCoord(gl_in[i].gl_Position.xyz);
					continue;
				}
				if (aRightPoint == toWinCoord(gl_in[aTriVertIter].gl_Position.xyz))
				{
					aRightPoint = toWinCoord(gl_in[i].gl_Position.xyz);
					continue;
				}
			}
		}
		vec3 aLeftVec = aLeftPoint - toWinCoord(gl_in[aTriVertIter].gl_Position.xyz);
		vec3 aRightVec = aRightPoint - toWinCoord(gl_in[aTriVertIter].gl_Position.xyz);
		float aAngle = acos(dot(aLeftVec, aRightVec) / (length(aLeftVec) * length(aRightVec)));
		float aScaleFactor = theValue / sin(aAngle / 2.0);
		vec3 aMoveVec = normalize(normalize(aLeftVec) + normalize(aRightVec));
		vec3 aVertRes = toWinCoord(gl_in[aTriVertIter].gl_Position.xyz) + aMoveVec * aScaleFactor;
		gl_Position = aMat * vec4 (toObjectCoord(aVertRes), 1.0);
		EmitVertex();
	}
}


void shrinkQuad(float theValue)
{	
	vec3 aWinCoordCenter = toWinCoord(vec3(0.0, 0.0, 0.0));
	aWinCoordCenter.xy += theValue;
	float aShift = length(toObjectCoord(aWinCoordCenter)) - theValue * 0.075;
	
	for (int aTriVertIter = 0; aTriVertIter < 3; ++aTriVertIter) 
	{
		vec3 aLeftPoint = gl_in[aTriVertIter].gl_Position.xyz;
		vec3 aRightPoint = gl_in[aTriVertIter].gl_Position.xyz;
		for(int i = 0; i < gl_in.length(); i++)
		{
			if(gl_in[i].gl_Position.xyz == gl_in[aTriVertIter].gl_Position.xyz)
			{
				continue;
			}
			else
			{
				if (aLeftPoint == gl_in[aTriVertIter].gl_Position.xyz)
				{
					aLeftPoint = gl_in[i].gl_Position.xyz;
					continue;
				}
				if (aRightPoint == gl_in[aTriVertIter].gl_Position.xyz)
				{
					aRightPoint = gl_in[i].gl_Position.xyz;
					continue;
				}
			}
		}
		vec3 aLeftVec = aLeftPoint - gl_in[aTriVertIter].gl_Position.xyz;
		vec3 aRightVec = aRightPoint - gl_in[aTriVertIter].gl_Position.xyz;
		float aAngle = acos(dot(aLeftVec, aRightVec) / (length(aLeftVec) * length(aRightVec)));	
		vec3 aSideCenter = (gl_in[0].gl_Position.xyz + gl_in[1].gl_Position.xyz) / 2;
		vec3 aMoveVec = normalize(aSideCenter - gl_in[aTriVertIter].gl_Position.xyz);
		if(aTriVertIter == 2)
		{
			aAngle /= 2.0;
			aMoveVec = normalize(normalize(aLeftVec) + normalize(aRightVec));
		}		
		float aScaleFactor = aShift / sin(aAngle);
		vec3 aVertRes = gl_in[aTriVertIter].gl_Position.xyz + aMoveVec * aScaleFactor;
		gl_Position = aMat * vec4 (aVertRes, 1.0);
		EmitVertex();
	}
}

void main() {
//	shrinkTrianglePix(10);
	shrinkTriangle(10);
//	shrinkQuad(10);		
	EndPrimitive();
}