Rewrite gl_pointsize for directx11

Hi everyone,

am rendering point clouds / particle systems successfully with PSIZE in opengl or direct3d... But switching player settings to directx11 on win10 (for HTC Vive game) the point size can no longer be changed. I have found a number of theories in google searches, but no code. How can I rewrite:

struct VertexOutput {

float4 pos : SV_POSITION;
float4 col : COLOR;
float pointSize : PSIZE;
};


VertexOutput vert(VertexInput v) {

VertexOutput o;
o.pos = mul(UNITY_MATRIX_MVP, v.v);
o.col = v.color;
o.pointSize = _PointSize;

return o;
}

in the shader code to draw/emit quads instead of points?

thank you for any help - please with code examples, since shaders are pretty tough to debug...