Temporary fix for mesh rasterization bug for traingles partially behind the camera

Summary: A triangle is culled if any vertex in a triangle is behind the camera.  This fixes incorrect rendering of triangles that are partially behind the camera, where screen coordinate calculations are strange.  It doesn't work for triangles that are partially behind the camera but still intersect with the view frustum.

Reviewed By: nikhilaravi

Differential Revision: D22856181

fbshipit-source-id: a9cbaa1327d89601b83d0dfd3e4a04f934a4a213
This commit is contained in:
Steve Branson 2020-08-20 22:23:06 -07:00 committed by Facebook GitHub Bot
parent 57a22e7306
commit 9aaba0483c
4 changed files with 39 additions and 8 deletions

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@ -90,8 +90,14 @@ __device__ bool CheckPointOutsideBoundingBox(
const float x_max = xlims.y + blur_radius;
const float y_max = ylims.y + blur_radius;
// Faces with at least one vertex behind the camera won't render correctly
// and should be removed or clipped before calling the rasterizer
const bool z_invalid = zlims.x < kEpsilon;
// Check if the current point is oustside the triangle bounding box.
return (pxy.x > x_max || pxy.x < x_min || pxy.y > y_max || pxy.y < y_min);
return (
pxy.x > x_max || pxy.x < x_min || pxy.y > y_max || pxy.y < y_min ||
z_invalid);
}
// This function checks if a pixel given by xy location pxy lies within the
@ -625,10 +631,13 @@ __global__ void RasterizeMeshesCoarseCudaKernel(
float ymin = FloatMin3(v0.y, v1.y, v2.y) - sqrt(blur_radius);
float xmax = FloatMax3(v0.x, v1.x, v2.x) + sqrt(blur_radius);
float ymax = FloatMax3(v0.y, v1.y, v2.y) + sqrt(blur_radius);
float zmax = FloatMax3(v0.z, v1.z, v2.z);
float zmin = FloatMin3(v0.z, v1.z, v2.z);
if (zmax < 0) {
continue; // Face is behind the camera.
// Faces with at least one vertex behind the camera won't render
// correctly and should be removed or clipped before calling the
// rasterizer
if (zmin < kEpsilon) {
continue;
}
// Brute-force search over all bins; TODO(T54294966) something smarter.

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@ -68,8 +68,12 @@ bool CheckPointOutsideBoundingBox(
float x_max = face_bbox[2] + blur_radius;
float y_max = face_bbox[3] + blur_radius;
// Faces with at least one vertex behind the camera won't render correctly
// and should be removed or clipped before calling the rasterizer
const bool z_invalid = face_bbox[4] < kEpsilon;
// Check if the current point is within the triangle bounding box.
return (px > x_max || px < x_min || py > y_max || py < y_min);
return (px > x_max || px < x_min || py > y_max || py < y_min || z_invalid);
}
// Calculate areas of all faces. Returns a tensor of shape (total_faces, 1)
@ -468,10 +472,13 @@ torch::Tensor RasterizeMeshesCoarseCpu(
float face_y_min = face_bboxes_a[f][1] - std::sqrt(blur_radius);
float face_x_max = face_bboxes_a[f][2] + std::sqrt(blur_radius);
float face_y_max = face_bboxes_a[f][3] + std::sqrt(blur_radius);
float face_z_max = face_bboxes_a[f][5];
float face_z_min = face_bboxes_a[f][4];
if (face_z_max < 0) {
continue; // Face is behind the camera.
// Faces with at least one vertex behind the camera won't render
// correctly and should be removed or clipped before calling the
// rasterizer
if (face_z_min < kEpsilon) {
continue;
}
// Use a half-open interval so that faces exactly on the

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@ -301,6 +301,7 @@ def rasterize_meshes_python(
x_maxs = torch.max(faces_verts[:, :, 0], dim=1, keepdim=True).values
y_mins = torch.min(faces_verts[:, :, 1], dim=1, keepdim=True).values
y_maxs = torch.max(faces_verts[:, :, 1], dim=1, keepdim=True).values
z_mins = torch.min(faces_verts[:, :, 2], dim=1, keepdim=True).values
# Expand by blur radius.
x_mins = x_mins - np.sqrt(blur_radius) - kEpsilon
@ -351,6 +352,12 @@ def rasterize_meshes_python(
or yf > y_maxs[f]
)
# Faces with at least one vertex behind the camera won't
# render correctly and should be removed or clipped before
# calling the rasterizer
if z_mins[f] < kEpsilon:
continue
# Check if pixel is outside of face bbox.
if outside_bbox:
continue

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@ -552,6 +552,10 @@ class TestRasterizeMeshes(TestCaseMixin, unittest.TestCase):
+ (zbuf1 * grad_zbuf).sum()
+ (bary1 * grad_bary).sum()
)
# avoid gradient error if rasterize_meshes_python() culls all triangles
loss1 += grad_var1.sum() * 0.0
loss1.backward()
grad_verts1 = grad_var1.grad.data.clone().cpu()
@ -563,6 +567,10 @@ class TestRasterizeMeshes(TestCaseMixin, unittest.TestCase):
+ (zbuf2 * grad_zbuf).sum()
+ (bary2 * grad_bary).sum()
)
# avoid gradient error if rasterize_meshes_python() culls all triangles
loss2 += grad_var2.sum() * 0.0
grad_var1.grad.data.zero_()
loss2.backward()
grad_verts2 = grad_var2.grad.data.clone().cpu()