Quad Mesh Primitives and Texture Mapping for Grids

Generate quad mesh primitives from the compact specification of a regular grid, its dimension and extent. Provides fast generation of mesh indexes and vertices, an unexpanded intermediate form (the grid edge coordinates), and a compact serializable specification for meshes that are generated on demand. Meshes are 'mesh3d' objects as used by the 'rgl' package, constructed without requiring any graphics engine, with support for texture mapping (Heckbert (1986) ) where an image is draped over a mesh whose density is independent of the image resolution. A C++ header library is installed so that other packages may generate mesh components via 'LinkingTo'.

textures

The goal of textures is to generate quad mesh primitives from the compact specification of a regular grid, its dimension and extent. The original motivation was to use texture mapping in graphics to work with images in different coordinate systems and mapped onto arbitrary shapes.

We aim to illustrate texture mapping capability in rgl with core techniques familiar to R users, and with minimal resort to specialist code. When specialist code is required it will be brought out explicitly and explained in a single-step.

Design

Current functions are:

• png_plot3d() - plots a PNG file in a 3D scene
• quad() create a simple mesh3d object with 1 or more quad primitives
• quad_texture() create a mesh3d object with 1 or more quads, and the texture coordinates and file path to a PNG file
• set_scene() a convenience wrapper to rgl scene settings, it makes the scene look “straight-down” and locks pan and tilt so the rgl device like a zoom-in/zoom-out 2D displays
• break_mesh() break the topology of a mesh (so that primitives can be free-floating, not tied to their neighbour’s vertices)

See design vignette.

Installation

Install from github, will require development tools for compiling code.

## install.packages("remotes")
remotes::install_github("hypertidy/textures")

Example

A Mercator raster on a single quad. Zoom in and out but no translate or pivot.

Maps an image onto a quad from a PNG file. Run this code and zoom in and out.

library(textures)
## create a temporary file and write an image to it
tfile <- tempfile(fileext = ".png")
png::writePNG(ga_topo$img/255, tfile)

## create a quad *canvas*, a single 4-corner shape floating in 3D
## (and use the PNG file as the material to texture that canvas)
quad0 <- quad_texture(c(1, 1), extent = ga_topo$extent, texture = tfile, )


## plot it in 3D 
rgl::open3d()
rgl::plot3d(quad0, specular = "black")
set_scene()  ## this sets the plot up to appear like a 2D image

Maps are fun but R is not just about geography.

library(ggplot2)
library(rgl)
## create a plot and save it
g <- ggplot(mpg, aes(displ, fill = drv)) + 
  geom_histogram(binwidth = 0.5) + 
  facet_wrap(~drv, ncol = 1)
g

tfile <- tempfile(fileext = ".png")
ggsave(tfile, g)


library(textures)
quad0 <- quad_texture(dimension = c(92, 102), texture = tfile)

ex <- -20
## flip it (fixme later)
quad0$vb[1L, ] <- 1-quad0$vb[1L, ]
quad0$vb[2L, ] <- 1-quad0$vb[2L, ]

quad0$vb[1L,] <- scales::rescale(quad0$vb[1,], to = c(-1, 1) * ex)
quad0$vb[2L,] <- scales::rescale(quad0$vb[2L,], to = c(-1, 1) * ex)

f <- function(x, y) { r <- sqrt(x^2+y^2); 10 * sin(r)/r }  ## ?persp
quad0$vb[3L, ] <- f(quad0$vb[1L,], quad0$vb[2L,])

## not working atm ...
#quad0 <- addNormals(quad0)  ## we are still in rgl scope, so everything is available
## plot it in 3D 
rgl::open3d()
rgl::plot3d(quad0, specular = "black")
rgl::aspect3d(1, 1, .3)
#set_scene(phi = 15, interactive = TRUE)
par3d(windowRect  = c(0, 0, 1024, 1024))

Code of Conduct

Please note that the textures project is released with a Contributor Code of Conduct. By contributing to this project, you agree to abide by its terms.