这是一个建议。策略如下：
- 让查看器构建
png
- 将
png从查看器发送到R
让查看器构建png
一个canvas image拥有一个.toDataURL() method，它返回一个数据URI，其中包含png格式的图像表示（我们也可以得到jpeg格式）。
html2canvas library 可用于截屏：此库将当前页面呈现为canvas 图像。
所以，可以在查看器中组合这两个功能：
- 用
html2canvas截图
- 使用
.toDataURL()将此屏幕截图转换为png
但是，html2canvas 库使用（Windows 版本）RStudio 查看器不支持的 JavaScript Promises：需要 polyfill。
将png 从查看器发送到 R
这个任务可以使用WebSockets来完成。
httpuv 包可用于创建网络服务器。此服务器将提供一个HTML 页面，该页面将在RStudio 查看器中打开。
httpuv 服务器和 RStudio 查看器之间建立了 WebSocket 通信。
从 R 命令行，可以向 RStudio 查看器发送一条 WebSocket 消息：接收到此消息，查看器截取屏幕截图并将其发送回服务器。
代码
对不起，这个代码对于一个 SO 答案来说很长。
library(httpuv)
# Initialize variables
png <- NULL
websocket <- NULL
# Download Javascript libraries
polyfill_promise <- readLines('https://cdn.jsdelivr.net/npm/es6-promise/dist/es6-promise.auto.min.js')
html2canvas <- readLines('https://html2canvas.hertzen.com/dist/html2canvas.min.js')
# Configure the httpuv server
app <- list(
call = function(req) {
list(
status = 200L,
headers = list(
'Content-Type' = 'text/html'
),
body = paste0(collapse = "\r\n",
c("<!DOCTYPE html>",
"<html>",
"<head>",
# polyfill the RStudio viewer to support JavaScript promises
'<script type="text/javascript">',
polyfill_promise,
"</script>",
# use html2canvas library
'<script type="text/javascript">',
html2canvas,
"</script>",
"</head>",
"<body>",
html_body,
"</body>",
'<script type="text/javascript">',
# Configure the client-side websocket connection:
'var ws = new WebSocket("ws://" + location.host);',
# When a websocket message is received:
"ws.onmessage = function(event) {",
# Take a screenshot of the HTML body element
" html2canvas(document.body).then(function(canvas) {",
# Transform it to png
" var dataURL = canvas.toDataURL();",
# Send it back to the server
" ws.send(dataURL);",
" });",
"};",
"</script>",
"</html>"
)
)
)
},
# Configure the server-side websocket connection
onWSOpen = function(ws) {
# because we need to send websocket message from the R command line:
websocket <<- ws
# when a websocket message is received from the client
ws$onMessage(function(binary, message) {
png <<- message
})
}
)
# From your question:
html_body <- c(
'<h1> Content</h1>',
'<h2> Content</h2>',
'lorem ipsum...'
)
# Start the server:
server <- startDaemonizedServer("0.0.0.0", 9454, app)
# Open the RStudio viewer:
rstudioapi::viewer("http://localhost:9454")
# Wait to see the result...
# Send a websocket message from the command line:
websocket$send("go") # send any message
# Write the png image to disk:
writeBin(
RCurl::base64Decode(
gsub("data:image/png;base64,", "", png),
"raw"
),
"screenshot.png"
)
# Close the websocket connection
websocket$close()
# Stop the server
stopDaemonizedServer(server)