update strategy for vignette prebuilding

.Rbuildignore

@@ -5,5 +5,6 @@
 ^docs$
 ^pkgdown$
 ^\.github$
+^build-vignettes\.md$
 ^cran-comments\.md$
 ^CRAN-SUBMISSION$

build-vignettes.md

@@ -0,0 +1,12 @@
+Due to the time-consuming computations involved in the vignettes of the *cisp* package, 
+it is necessary to pre-build the vignettes prior to package submission.
+
+``` r
+.prebuild_vignettes = \(name){
+  out = paste0("vignettes/",name,".Rmd")
+  inp = paste0(out,".orig")
+  knitr::knit(inp,out)
+}
+
+.prebuild_vignettes("cisp")
+```

vignettes/cisp.rmd

@@ -65,7 +65,7 @@ system.time({
   g = cisp::spc(ndvi,cores = 6)
 })
 ##    user  system elapsed 
-##    0.84    0.20   21.50
+##    0.66    0.26   24.88
 g
 ## ***   Spatial Pattern Correlation    
 ##