Mesh Paint mode's Texture Paint has obvious artifact with UV seams

Mesh Painting Texture Paint tool can miss some pixels along UV seams, even with "Enable Seam Painting" set to True.

This appears to be because of the difference between rasterization and sampling. With rasterization, a pixel is only rendered to if its center is within a rasterized triangle. When sampling, a pixel will be sampled if any part of it is within the triangle.

This leads to fine edges where some pixels are not written to during Mesh Paint, but are sampled in the material.

Also tested on //UE5//Release-5.5, CL: 36860055

• 1. Download the Licensee's test project and open (see addl info URL)
  2. Open the map /Game/TexturePaintTest/Levels/TexturePaintTest_P
  3. Replace the mesh on the actor "zzTestMeshN" with the Static Mesh "zzTestMesh". This is the non-Nanite version.
  4. Enter Mesh Paint mode, select the sub-mode "Textures", and the "Paint" tool.
  5. Make sure the Paint Texture is set to "T_MaskRGB".
  6. Enable "Enable Seam Painting"
  7. Set the brush strength to be 1, and the falloff to be 0.
  8. Paint along the mesh's vertical edges, and top edge.
  9. Observe the fine seam that is not painted

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