set_panel_size.r

require(grid)
require(ggplot2)


set_panel_size <- function(p=NULL, g=ggplotGrob(p), width=unit(3, "cm"), height=unit(3, "cm")){
  panel_index_w<- g$layout$l[g$layout$name=="panel"]
  panel_index_h<- g$layout$t[g$layout$name=="panel"]
  g$widths[[panel_index_w]] <- width
  g$heights[[panel_index_h]] <- height
  class(g) <- c("fixed", class(g), "ggplot")
  g
}

print.fixed <- function(x) grid.draw(x)

left_width <- function(g){
  axis_l_index <- g$layout$r[g$layout$name=="axis-l"]
  ylab_index <- g$layout$r[g$layout$name=="ylab"]
  g$widths[[axis_l_index]] + g$widths[[ylab_index]]
}

full_width <- function(g){
  sum(g$widths)
}


align_plots <- function(..., width=unit(3, "cm"), height=unit(1, "null")){

  pl <- list(...)
  gl <- lapply(pl, set_panel_size, width=width, height=height)
  
  left <- lapply(gl, left_width)
  max_left <- max(do.call(unit.c, left))

  widths <- lapply(gl, full_width)
  max_width <- max(do.call(unit.c, widths))
  
  lay <- grid.layout(nrow=length(gl), ncol=1)
  vp <- viewport(layout=lay)
  pushViewport(vp)
  
  for(ii in seq_along(gl)){
    pushViewport(viewport(layout.pos.row=ii))
    pushViewport(viewport(x=unit(0.5, "npc") - 0.5*max_width + max_left - left[[ii]],
                          just="left", width=widths[[ii]]))
    grid.draw(gl[[ii]])
    upViewport(2)
  }
  upViewport()
}