simple warning for bin overflow

Summary: Since coarse rasterization on cuda can overflow bins, we detect when this happens for memory safety. See #348 . Also try to print a warning.

Reviewed By: patricklabatut

Differential Revision: D33065604

fbshipit-source-id: 99b3c576d01b78e6d77776cf1a3e95984506c93a

Author: bottler

pytorch3d/csrc/rasterize_coarse/rasterize_coarse.cu

@@ -183,6 +183,22 @@ __global__ void RasterizeCoarseCudaKernel(
       // this effectively allocates space in the bin_faces array for the
       // elems in the current chunk that fall into this bin.
       const int start = atomicAdd(elems_per_bin + elems_per_bin_idx, count);
+      if (start + count > M) {
+        // The number of elems in this bin is so big that they won't fit.
+        // We print a warning using CUDA's printf. This may be invisible
+        // to notebook users, but apparent to others. It would be nice to
+        // also have a Python-friendly warning, but it is not obvious
+        // how to do this without slowing down the normal case.
+        const char* warning =
+            "Bin size was too small in the coarse rasterization phase. "
+            "This caused an overflow, meaning output may be incomplete. "
+            "To solve, "
+            "try increasing max_faces_per_bin / max_points_per_bin, "
+            "decreasing bin_size, "
+            "or setting bin_size to -1 to use the naive rasterization.";
+        printf(warning);
+        continue;
+      }
 
       // Now loop over the binmask and write the active bits for this bin
       // out to bin_faces.