com.unity.uiwidgets/Runtime/Resources/UIWidgets_canvas_cb.cginc

struct vdata
            {
                float2 vertex;
                float2 uv;
            };

            struct psInput
            {
                float4 position : SV_POSITION;
            };

            StructuredBuffer<vdata> databuffer;
            StructuredBuffer<int> indexbuffer;
            float4 _viewport;
            int _startVertex;
            
            psInput vert (uint vertex_id: SV_VertexID, uint instance_id: SV_InstanceID)
            {
                psInput o = (psInput)0;
                o.position = float4(databuffer[indexbuffer[_startVertex + vertex_id]].vertex.x * 2.0 / _viewport.z - 1.0, databuffer[indexbuffer[_startVertex + vertex_id]].vertex.y * 2.0 / _viewport.w - 1.0, 0, 1);
                return o;
            }
            
            fixed4 frag (psInput i) : SV_Target
            {
                return float4(0, 1, 0, 1);
            }