R 绘图 ggplot png 所支持的最大图片背景与res的关系

问题描述

在使用R脚本绘图时，有的图片背景需要根据数据大小调整（自适应图片大小的方法见:https://www.jianshu.com/p/aedb5cfd43dc），这时如果图片太大超出png的范围，会报错；Rstudio报错信息为：

Error in png(filename = "cluster_detail_heatmap.png", width = size, height = size,  : 
  无法启动png()装置
In addition: Warning messages:
1: In png(filename = "cluster_detail_heatmap.png", width = size, height = size,  :
  无法分配bitmap
2: In png(filename = "cluster_detail_heatmap.png", width = size, height = size,  :
  opening device failed

终端执行R脚本，报错信息为：

Error in png(filename = "tmp.png", width = sz, height = sz, units = "cm",  :
  unable to start device 'png'
此外: Warning message:
In png(filename = "tmp.png", width = sz, height = sz, units = "cm",  :
  cairo error 'invalid value (typically too big) for the size of the input (surface, pattern, etc.)'
停止执行

问题解决

下面是查看在不同环境下所支持的png最大尺寸与res关系的R脚本：

# 需要输入两个参数
# $1 png size ;example: 1000 (png的大小)
# $2 res num; png的res数值(一般300)


args <- commandArgs(T)
sz=as.numeric(args[1])
resnum <- as.numeric(args[2])

pngsz=function(size,resnum){
  png(filename = "tmp.png", width =size , height = size, units = "cm",res = resnum)
}
findmax=function(sz,resnum){
  st="Blank"
  while (st != "YES") {
    tryCatch({
      pngsz(sz,resnum)
      st="YES"
      dev.off()
      print(sz)
    },warning = function(w) {
    },error = function(e) {
    },finally = {
      maxsize=sz
      sz=sz-10  # 为输出的精度，-10表示真实值与输出值之差小于等于10
    })
  }
  cat("maxsize=",maxsize,"\n","res=",resnum,"\n")
  return (maxsize)
}
tryCatch({
  st="NO"
  pngsz(sz,resnum)
  st="YES"
  dev.off()
  print(sz)
},warning = function(w) {
},error = function(e) {
},finally = {
  maxsize=sz
})
#cat("st=",st,"\n")
if( st == "NO" ){
  print("find max png ......")
  maxsize=findmax(sz,resnum)
}else{
  print("输入的图片数字需要增大")
  print("The number of pictures entered needs to be increased")
}
if(st=="NO"){
  tryCatch({
    che="stat1"
    png(filename = "tmp.png", width =10 , height = (maxsize*maxsize)/10, units = "cm",res = resnum)
    dev.off()
    che="stat2"
  },warning = function(w) {
  },error = function(e) {
  },finally = {
  })
  if( che == "stat1" ){
    cat("当前环境当res为",resnum,"时，png的width 和height 最大值为",maxsize,"\n")
    cat(" In this device,when res=",resnum,";png limited width & height max=",maxsize,"\n")
  }else{
    cat("当前环境当res为",resnum,"时，png的width*height(面积)最大值为",maxsize*maxsize,"\n")
    cat(" In this device,when res=",resnum,";png limited width * height; max=",maxsize*maxsize,"\n")
  }
}

结论：

在Rstudio中，png的最大值为：width*height(面积)；在终端中width 和height 各有相同的最大值，都不能超出这个值

终端下res与png大小的关系图

image.png

这种函数图像是幂函数，通过函数拟合计算出公式：y = 83450.31x^-1；y为大小，x为分辨率，至此绘图自适应大小的问题已经得到彻底解决