HLSL Geometry Shader Thick Lines DirectX - directx

Question

I try to draw a thick lined Sinus curve using this approach : https://forum.libcinder.org/topic/smooth-thick-lines-using-geometry-shader
I tried to port it to HLSL geometry shader:
Setting the dimension to fix 500/500 atm
THICKNESS seems not to change the issue
struct PSInput
{
float4 Position : SV_POSITION;
};
float2 toScreenSpace(float4 vertex)
{
float2 WIN_SCALE = { 500.0f, 500.0f };
return float2(vertex.xy / vertex.w) * WIN_SCALE;
}
[maxvertexcount(7)]
void main(lineadj float4 vertices[4] : SV_POSITION, inout TriangleStream<PSInput> triStream)
{
float2 WIN_SCALE = { 500.0f, 500.0f };
float2 p0 = toScreenSpace(vertices[0]); // start of previous segment
float2 p1 = toScreenSpace(vertices[1]); // end of previous segment, start of current segment
float2 p2 = toScreenSpace(vertices[2]); // end of current segment, start of next segment
float2 p3 = toScreenSpace(vertices[3]); // end of next segment
// perform naive culling
float2 area = WIN_SCALE * 1.2;
if (p1.x < -area.x || p1.x > area.x)
return;
if (p1.y < -area.y || p1.y > area.y)
return;
if (p2.x < -area.x || p2.x > area.x)
return;
if (p2.y < -area.y || p2.y > area.y)
return;
float2 v0 = normalize(p1 - p0);
float2 v1 = normalize(p2 - p1);
float2 v2 = normalize(p3 - p2);
// determine the normal of each of the 3 segments (previous, current, next)
float2 n0 = { -v0.y, v0.x};
float2 n1 = { -v1.y, v1.x};
float2 n2 = { -v2.y, v2.x};
// determine miter lines by averaging the normals of the 2 segments
float2 miter_a = normalize(n0 + n1); // miter at start of current segment
float2 miter_b = normalize(n1 + n2); // miter at end of current segment
// determine the length of the miter by projecting it onto normal and then inverse it
float THICKNESS = 1;
float length_a = THICKNESS / dot(miter_a, n1);
float length_b = THICKNESS / dot(miter_b, n1);
float MITER_LIMIT = 0.75;
//float MITER_LIMIT = -1;
//float MITER_LIMIT = 0.1;
PSInput v;
float2 temp;
//// prevent excessively long miters at sharp corners
if (dot(v0, v1) < -MITER_LIMIT)
{
miter_a = n1;
length_a = THICKNESS;
// close the gap
if (dot(v0, n1) > 0)
{
temp = (p1 + THICKNESS * n0) / WIN_SCALE;
v.Position = float4(temp, 1.0, 1.0);
triStream.Append(v);
temp = (p1 + THICKNESS * n1) / WIN_SCALE;
v.Position = float4(temp, 1.0, 1.0);
triStream.Append(v);
v.Position = float4(p1 / WIN_SCALE, 1.0, 1.0);
triStream.Append(v);
//triStream.RestartStrip();
}
else
{
temp = (p1 - THICKNESS * n1) / WIN_SCALE;
v.Position = float4(temp, 1.0, 1.0);
triStream.Append(v);
temp = (p1 - THICKNESS * n0) / WIN_SCALE;
v.Position = float4(temp, 1.0, 1.0);
triStream.Append(v);
v.Position = float4(p1 / WIN_SCALE, 1.0, 1.0);
triStream.Append(v);
//triStream.RestartStrip();
}
}
if (dot(v1, v2) < -MITER_LIMIT)
{
miter_b = n1;
length_b = THICKNESS;
}
// generate the triangle strip
temp = (p1 + length_a * miter_a) / WIN_SCALE;
v.Position = float4(temp, 1.0, 1.0);
triStream.Append(v);
temp = (p1 - length_a * miter_a) / WIN_SCALE;
v.Position = float4(temp, 1.0, 1.0);
triStream.Append(v);
temp = (p2 + length_b * miter_b) / WIN_SCALE;
v.Position = float4(temp, 1.0, 1.0);
triStream.Append(v);
temp = (p2 - length_b * miter_b) / WIN_SCALE;
v.Position = float4(temp, 1.0, 1.0);
triStream.Append(v);
//triStream.RestartStrip();
}
The thing is, that it won't output anything of the curve I give as points to it. It already works very well without thick lines, but I want to have that. I can add Noise to my Sinus signal and if I do that, (y-values increase by a little random %) suddenly the curve shows up and is thicker and seems to work, but I want it to be thick and showing without noise too.
If I up the frequency, without noise, point appear scattered-plot style, but not as a connected Sinus.
If I debug with the VS Graphics Debugger, I can see that in the frame with no Noise it says the Pixel-Shader-Stage is not run (?).
The frame with noise shows it run and working.
Maybe my porting is incorrect and I forget something, I am very new to programming shaders. Maybe I missunderstand the approach at all.
Any help appreciated.

Answer 1

I needed to set the default behavior of the culling to CullMode.None to get all the triangle drawn.