---
title: "design - textures package"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{design}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
```


## Design 


Both **quad()** and **quad_texture()** return 'mesh3d' objects that may be plotted directly with
 rgls `plot3d()`, `shade3d()`, `persp3d()`, `wire3d()`, or `dot3d()`. 


* All coordinates are in  `x [0, 1]` and `y [0, 1]` and default to "y-up" (begin at 0)
* Quad indexes are counter-clockwise, as required by rgl (see `material3d` `back` argument).
* `ydown` flips the orientation so that y coordinates begin at 1 and count down, and ensures that quad indexes are reversed and correctly counter-clockwise. 

### R functions using src/

* `break_mesh()` - removes topology from mesh3d, by expanding every coordinate from vertex array
* `quad()` generate mesh3d, a rectangular array of quads in the plane in 0,1
* `quad_texture()` - extension of quad() to include image texture, all geometry and texture has identical x-y plane coordinates in 0,1


### Rcpp package using quad.h

These are callable from R. 

```C++
IntegerVector quad_index_cpp(IntegerVector nx, IntegerVector ny, LogicalVector ydown) 
NumericVector quad_vertex_cpp(IntegerVector nx, IntegerVector ny, LogicalVector ydown, LogicalVector zh) 
NumericVector quad_vertex_matrix_cpp(IntegerVector nx, IntegerVector ny, LogicalVector ydown, LogicalVector zh) 

```

### Headers 

`quad_ib` and `quad_vb` both return flat vectors, `quad_matrix_vb` returns a matrix
(with optionally z and h). 

`./inst/include/quad/quad.h` namespace `quad`

```C++
IntegerVector quad_ib(IntegerVector nx, IntegerVector ny, LogicalVector ydown, LogicalVector zh);
NumericVector quad_vb(IntegerVector nx, IntegerVector ny, LogicalVector ydown, LogicalVector zh);
NumericVector quad_matrix_vb(IntegerVector nx, IntegerVector ny, LogicalVector ydown, LogicalVector zh);

```