diff --git a/R/knitr.R b/R/knitr.R
index 339c45db6..e404638d1 100644
--- a/R/knitr.R
+++ b/R/knitr.R
@@ -258,7 +258,11 @@ fns <- local({
                                          left   = "margin-left:0;margin-right:auto;",
                                          right  = "margin-left:auto;margin-right:0;",
                                          ""))))
-    result <- do.call("knit_print", c(list(content, options), x$args))
+    # Not sure why this wasn't there for our vignettes...
+    if (!("screenshot.force" %in% names(options)))
+      options$screenshot.force <- FALSE
+    
+    result <- do.call("knit_print", c(list(x = content, options = options), x$args))
     if (!latex)
       class(result) <- c(class(result), "knit_asis_htmlwidget")
     
diff --git a/R/rglwidget.R b/R/rglwidget.R
index 6d921c4a8..6246b9709 100644
--- a/R/rglwidget.R
+++ b/R/rglwidget.R
@@ -241,12 +241,25 @@ asRow <- function(..., last = NA, height = NULL, colsize = 1) {
 newElementId <- function(prefix)
   paste0(prefix, p_sample(100000, 1))
 
+isMarkdownHTMLformat <- function() {
+  output <- rmarkdown::metadata$output
+  
+  if (is.list(output))
+    output <- names(output)
+  
+  is.character(output) && 
+    length(output) >= 1 &&
+    output[1] == "markdown::html_format"
+}
+
 knitrNeedsSnapshot <- function(options = knitr::opts_current$get()) {
   if (!is.null(options$snapshot))
     return(options$snapshot)
   if (isFALSE(options$screenshot.force))
     return(FALSE)
   force <- isTRUE(options$screenshot.force)
+  if (isMarkdownHTMLformat())
+    return(FALSE)
   fmt <- pandoc_to()
   if (!length(fmt) || force)
     return(TRUE)
diff --git a/man/snapshot.Rd b/man/snapshot.Rd
index 4b27792bc..461e06ef6 100644
--- a/man/snapshot.Rd
+++ b/man/snapshot.Rd
@@ -29,10 +29,13 @@ Ignored if \code{webshot = TRUE}.}
 \details{
 \code{rgl.snapshot()} is a low-level function
 that copies the current RGL window from the screen.  Users
-should use \code{snapshot3d()} instead; it is more flexible,
+should usually use \code{snapshot3d()} instead; it is more flexible,
 and (if \pkg{webshot2} is installed) can take images even if
 no window is showing, and they can be larger than the physical
-screen.
+screen.  On some systems \pkg{webshot2} doesn't work reliably; if
+you find \code{snapshot3d()} failing or taking a very long time
+I'd recommend using \code{snapshot3d(..., webshot = FALSE)}.  See
+the note below about \code{RGL_USE_WEBSHOT} to make this the default.
 
 Animations can be created in a loop modifying the scene and saving 
 each screenshot to a file. Various graphics programs (e.g. ImageMagick)
diff --git a/vignettes/demos.Rmd b/vignettes/demos.Rmd
index 475a53171..4368aafd6 100644
--- a/vignettes/demos.Rmd
+++ b/vignettes/demos.Rmd
@@ -14,7 +14,9 @@ vignette: >
 ```{r setup, include = FALSE}
 knitr::opts_chunk$set(
   collapse = FALSE,  # Bug in knitr 1.42 requires FALSE here
-  comment = "#>")
+  comment = "#>",
+  snapshot = FALSE,
+  screenshot.force = FALSE)
 library(rgl)
 setupKnitr(autoprint = TRUE)
 ```
diff --git a/vignettes/pkgdown.Rmd b/vignettes/pkgdown.Rmd
index fb5d1169e..5ed76a19c 100644
--- a/vignettes/pkgdown.Rmd
+++ b/vignettes/pkgdown.Rmd
@@ -25,7 +25,7 @@ if (!requireNamespace("rmarkdown", quietly = TRUE)) {
   warning(call. = FALSE, "These vignettes assume rmarkdown.  This was not found.")
   knitr::knit_exit()
 }
-knitr::opts_chunk$set(echo = TRUE)
+knitr::opts_chunk$set(echo = TRUE, snapshot = FALSE, screenshot.force = FALSE)
 library(rgl)
 options(rgl.useNULL = TRUE)
 setupKnitr(autoprint = TRUE)
diff --git a/vignettes/setup.R b/vignettes/setup.R
index 62261c6c2..9ffc67947 100644
--- a/vignettes/setup.R
+++ b/vignettes/setup.R
@@ -14,7 +14,7 @@ if (!requireNamespace("rmarkdown", quietly = TRUE)) {
 # knitr uses it to determine whether to do
 # screenshots; we don't want those. see https://github.com/rstudio/markdown/issues/115
 
-knitr::opts_knit$set(screenshot.force = FALSE)
+knitr::opts_chunk$set(screenshot.force = FALSE, snapshot = FALSE)
   
 # knitr::opts_chunk$set(snapshot = TRUE)  # for snapshots instead of dynamic
 
diff --git a/vignettes/transparency.Rmd b/vignettes/transparency.Rmd
index 4b5d0f9ca..cbaa7afde 100644
--- a/vignettes/transparency.Rmd
+++ b/vignettes/transparency.Rmd
@@ -26,7 +26,7 @@ if (!requireNamespace("rmarkdown", quietly = TRUE)) {
   warning(call. = FALSE, "These vignettes assume rmarkdown is installed.  This was not found.")
   knitr::knit_exit()
 }
-knitr::opts_chunk$set(echo = TRUE)
+knitr::opts_chunk$set(echo = TRUE, snapshot = FALSE, screenshot.force = FALSE)
 library(rgl)
 options(rgl.useNULL = TRUE)
 setupKnitr(autoprint = TRUE)