Compact quad mesh specification

A quad mesh on a regular grid is completely determined by a tiny recipe: the grid dimension, its extent, and the y orientation. quad_spec() records that recipe as a plain, serializable list without materializing any vertices or indexes.

Usage

quad_spec(
  dimension = c(1L, 1L),
  extent = NULL,
  ydown = FALSE,
  crs = NULL,
  texture = NULL
)

quad_mesh(x, ...)

# S3 method for class 'quad_spec'
quad_mesh(x, ...)

# S3 method for class 'quad_spec'
as.mesh3d(x, ...)

# S3 method for class 'quad_spec'
print(x, ...)

Arguments

dimension

number of cells in the grid (nx, ny), a single value is recycled

extent

extent of the grid c(xmin, xmax, ymin, ymax), default is the unit square

ydown

should the y coordinate be counted from the top, default FALSE

crs

optional coordinate reference system, stored but not used by textures itself

texture

optional file path to a PNG image to texture onto the mesh when materialized

x

a quad_spec object

...

ignored, or passed between methods

Value

quad_spec() a list with class 'quad_spec', quad_mesh() a mesh3d object, the print method returns its input invisibly

Details

quad_mesh() materializes the specification as a 'mesh3d' object (as used by the 'rgl' package, but constructed without it). If the spec carries a texture image file path, texture coordinates are included: these are the extent-normalized vertex coordinates, so they remain valid for any mesh whose vertices lie in the extent.

With the 'rgl' package installed, as.mesh3d() works directly on a quad_spec (registered on-demand, 'rgl' is not required).

The mesh density given by dimension is independent of the pixel dimension of any texture image: a coarse mesh may carry a full-resolution image, the graphics engine interpolates within each quad.

A spec can be stored, serialized, and sent where a materialized mesh cannot sensibly be - materialization is deferred to the consumer.

See also

Other textures: break_mesh(), quad()

Examples

spec <- quad_spec(c(20, 10), extent = c(100, 160, -60, -30))
spec
#> <quad_spec>
#>   dimension : 20 x 10 cells (231 vertices)
#>   extent    : 100, 160, -60, -30 (xmin, xmax, ymin, ymax)
#>   ydown     : FALSE
mesh <- quad_mesh(spec)
str(mesh$vb)
#>  num [1:4, 1:231] 100 -60 0 1 103 -60 0 1 106 -60 ...