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Flip the texture coordinates of a mesh vertically

Source: R/mesh_utils.R
flip_uvs.Rd

scimesh stores texture coordinates in image space, with v = 0 at the top edge of the texture image — the same rule as every other coordinate in scimesh (c(0, 0) addresses the top-left pixel of the texture image, c(1, 1) the bottom-right one). OBJ and PLY files, OpenGL, rgl and tools like Blender and MeshLab use the opposite convention (v = 0 at the bottom), so UVs taken from those sources have to be converted once; this function does that, instead of you having to rewrite the second column by hand.

Usage

flip_uvs(mesh)

Arguments

mesh

A mesh descriptor (scimesh or rgl format, see as_scimesh_mesh()).

Value

The mesh with flipped UVs.

Details

Geometry, colors and normals are untouched. A mesh without texture coordinates is returned unchanged, so calling this is safe either way.

See also

render_mesh (the uv and texture arguments)

Examples

quad <- list(vertices = matrix(c(-1, -1, 0, 1, -1, 0, 1, 1, 0,
                                 -1, -1, 0, 1, 1, 0, -1, 1, 0),
                               ncol = 3, byrow = TRUE),
             triangles = matrix(c(1, 2, 3, 1, 3, 4), ncol = 3, byrow = TRUE),
             # UVs with v = 0 at the bottom (OBJ/OpenGL convention)
             uv = matrix(c(0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0),
                         ncol = 2, byrow = TRUE))
flipped <- flip_uvs(quad)
flipped$uv[, 2]  # v is now measured from the top of the texture
#> [1] 0 0 1 0 1 1