imageMap-methods: Write an HTML IMG tag together with a MAP image map.

Description

Write an HTML IMG tag together with a MAP image map.

Usage

"imageMap"(object, con, tags, imgname)

Arguments

object

Matrix with 4 columns, specifying the coordinates of the mouse-sensitive region . Each row specifies the corners of a rectangle within the image, in the following order: (left x, lower y, right x, upper y). Note that the point (x=0, y=0) is at the left upper side of the image.

con

Connection to which the image map is written.

Value

the connection con.

Details

The most important tags are TITLE, HREF, and TARGET. If the list tags contains an element with name TITLE, then this must be a named character vector containing the tooltips that are to be displayed when the mouse moves over a node. The names of the nodes are specified in the names attribute of the character vector and must match those of object. Similarly, HREF may be used to specify hyperlinks that the browser can follow when the mouse clicks on a node, and TARGET to specify the target browser window.

Currently, only rectangular regions are implemented; the actual shape of the nodes as specified in object is ignored. Also, tags for edges of the graph are currently not supported.

This function is typically used with the following sequence of steps:

generate your graphic and save it as a bitmap file, e.g. using the jpeg, png, or bitmap device. At this stage, you also need to figure out the pixel coordinates of the interesting regions within your graphic. Since the mapping between device coordinates and pixel coordinates is not obvious, this may be a little tricky. See the examples below, and for a more complex example, see the source code of the function plotPlate.
open an HTML page for writing and write HTML header, e.g. using the openHtmlPage function.
Call the imageMap function.
Optionally, write further text into the HTML connection.
Close HTML file, e.g. using the closeHtmlPage function.

Examples

Run this code

f1  = paste(tempfile(), ".html", sep="")
f2  = paste(tempfile(), ".html", sep="")
fpng = tempfile()

if(capabilities()["png"]) {
  ## create the image
  colors = c("#E41A1C","#377EB8","#4DAF4A","#984EA3","#FF7F00","#FFFF33","#A65628","#F781BF","#999999")
  width  = 512
  height = 256
  png(fpng, width=width, height=height)
  par(mai=rep(0,4))
  plot(0,xlim=c(0,width-1),ylim=c(0,height-1),xaxs="i",yaxs="i",type="n",bty="n")
  cx=floor(runif(100)*(width-11))
  cy=floor(runif(100)*(height-11))
  coord=cbind(cx, cy, cx+10, cy+10)
  rect(coord[,1], height-coord[,2], coord[,3], height-coord[,4],
       col=sample(colors, 100, replace=TRUE))
  text(width/2, height-3, "Klick me!", adj=c(0.5, 1), font=2)
  dev.off()

  ## create the frame set
  cat("<html><head><title>Hello world</title></head>\n",
      "<frameset rows=\"280,*\" border=\"0\">\n",
      "<frame name=\"banner\" src=\"file://", f2, "\">\n",
      "<frame name=\"main\" scrolling=\"auto\">",
      "</frameset>", sep="",file=f1)

  ## create the image map
  href  =sample(c("www.bioconductor.org", "www.r-project.org"),nrow(coord),replace=TRUE)
  title =sample(as.character(packageDescription("geneplotter")),nrow(coord),replace=TRUE)
  con = file(f2, open="w")
  imageMap(coord, con,
    list(HREF=paste("http://", href, sep=""),
         TITLE=title, TARGET=rep("main", nrow(coord))), fpng)
  close(con)

  cat("Now have a look at file ", f1, " with your browser.\n", sep="")
}