Fast and Reliable Mouse Picking Using Graphics Hardware

Algorithm 1

Object-based intersection test.

(1)   float 3×3 edge; float4 Picker

(2)   edge[0] = input[1] − input[0]

(3)   edge[1] = input[2] − input[0]

(4)   Picker.w = det(float3×3(−Ray, edge[0], edge[1])

(5)   if Picker.w == 0 then

(6)     return

(7)   end if

(8)   if Picker.w < 0 then

(9)    Picker.w = −Picker.w

(10)  edge[2] = input[0] − float3(0, 0, 0)

(11) else

(12)  edge[2] = float3(0, 0, 0) − input[0]

(13)  Picker.x = det(float3×3(−Ray, edge[2], edge[1])

(14) end if

(15) if Picker.x < 0 ∣∣ Picker.x > Picker.w

(16)   return

(17) end if

(18) Picker.y = det(float3×3(−Ray, edge[0], edge[2])

(19) if Picker.y < 0 ∣∣ Picker.x + Picker.y > Picker.w

(20)   return

(21) end if

(22) // get the distance in the view-space

(23) Picker.z = det(float3×3(edge[2], edge[0], edge[1])

(24) Picker.z = Picker.z / Picker.w ∗ PickingRay.z

(25) PICKING_GS_OUTPUT output

(26) output.Pos = float4(0, 0, Picker.z, 1)

(27) // transform the distance value into projection space

(28) output.Pos.zw = mul(output.Pos.zw,

    float2×2(mxProj[2].yz, mxProj[3].yz)

(29) output.Info = float4(Picker.xy/Picker.w, FacetID,

     ObjectID)

(30) outStream.Append(output)