Algorithm 1.
The PixelBox GPU algorithm.
| 1: | {pi, qi}i : the array of input polygon pairs |
| 2: | {mi}i : the MBR of each polygon pair |
| 3: | N : total number of polygon pairs |
| 4: | stack[] : the shared stack containing sampling boxes |
| 5: | I[N][blockDim.x] : partial areas of intersections |
| 6: | A[N][blockDim.x] : partial summed areas of polygons |
| 7: | |
| 8: | procedure Kernel_SampBox |
| 9: | tid ← threadIdx.x |
| 10: | for i = blockIdx.x to N do |
| 11: | A[i][tid] ← A[i][tid] + PolyArea(pi) |
| 12: | A[i][tid] ← A[i][tid] + PolyArea(qi) |
| 13: | Thread 0: stack[0] ← {mi, 1} |
| 14: | top ← 1 |
| 15: | while top > 0 do |
| 16: | top ← top − 1 |
| 17: | syncthreads() |
| 18: | {box, c} ← stack[top] |
| 19: | if c = 0 then |
| 20: | continue |
| 21: | else |
| 22: | if BoxSize(box) < T then |
| 23: | for j ← tid to BoxSize(box) do |
| 24: | ϕ1 ← PixelInPoly(box, j, pi) |
| 25: | ϕ2 ← PixelInPoly(box, j, qi) |
| 26: | I[i][tid] ← I[i][tid] + (ϕ1 ˄ ϕ2) |
| 27: | j ← j + blockDim.x |
| 28: | end for |
| 29: | else |
| 30: | subbox ← SubSampBox(box, tid) |
| 31: | ϕ1 ← BoxPosition(box, pi) |
| 32: | ϕ2 ← BoxPosition(box, qi) |
| 33: | c ← BoxContinue(ϕ1, ϕ2) |
| 34: | t ← BoxContribute(ϕ1, ϕ2) |
| 35: | a ← (1 − c) × t × BoxSize(subbox) |
| 36: | I[i][tid] ← I[i][tid] + a |
| 37: | stack[top + 1 + tid] ← {subbox, c} |
| 38: | Thread 0: stack[top].c ← 0 |
| 39: | top ← top + 1 + blockDim.x |
| 40: | end if |
| 41: | end if |
| 42: | end while |
| 43: | i ← i + gridDim.x |
| 44: | end for |
| 45: | end procedure |