bool FrontEndCullingByArea(VSOutput v0, VSOutput v1, VSOutput v2)
{
if (context.frontEndCull == FrontEndCull.Off)
{
return(true);
}
if (context.cullMode == CullMode.None)
{
return(true);
}
//cull back
Vector2 p0 = new Vector2(v0.position.X, v0.position.Y);
Vector2 p1 = new Vector2(v1.position.X, v1.position.Y);
Vector2 p2 = new Vector2(v2.position.X, v2.position.Y);
//做了透射除法,Culling准确点
p0 *= 1 / v0.position.W;
p1 *= 1 / v1.position.W;
p2 *= 1 / v2.position.W;
float area = Rasterizer.EdgeFunction(p0, p1, p2);
//在Clip Space, area >= 0表示顺时针
if (context.winding == Winding.Clockwise)
{
return(area > 0);
}
return(area < 0);
}
bool BackfaceCulling(VSOutput vScreen0, VSOutput vScreen1, VSOutput vScreen2)
{
if (context.cullMode == CullMode.None)
{
return(true);
}
if (context.frontEndCull == FrontEndCull.On)
{
return(true);
}
Vector2 p0 = new Vector2(vScreen0.posScreen.X, vScreen0.posScreen.Y);
Vector2 p1 = new Vector2(vScreen1.posScreen.X, vScreen1.posScreen.Y);
Vector2 p2 = new Vector2(vScreen2.posScreen.X, vScreen2.posScreen.Y);
float area = Rasterizer.EdgeFunction(p0, p1, p2);
if (context.winding == Winding.Clockwise)
{
return(area < 0);
}
//在Viewport Space, 由于Y轴向下, area > 0表示逆时针
return(area > 0);
}