# Colours! - A colourful demonstration of R's graphics.
# Copyright (C) December 2008 Neil Fraser
# http://neil.fraser.name/

# This program is free software; you can redistribute it and/or
# modify it under the terms of version 2 of the GNU General
# Public License as published by the Free Software Foundation.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# http://www.gnu.org/

# Height and width of the image.
# All values work, but 2^n+1 squares are ideal (65x65, 129x129, 257x257, etc).
rows = 257
cols = 257


# Pick a random number between two end values.
midpoint = function(end1, end2) {
  if (end1 > end2) {
    return(runif(1, end2, end1))
  } else {
    return(runif(1, end1, end2))
  }
}


# Recursively fill one row.
# Used to bootstrap the recursive area fill.
# Also used to fudge our way out of ?x2 rectangles.
fillrow = function(grid, row, endleft, endright) {
  if (endleft + 1 == endright)
    return(grid)
  # Set the dot in the middle.
  middleX = floor((endright - endleft) / 2 + endleft)
  grid[middleX, row] = midpoint(grid[endleft, row], grid[endright, row])
  # Go fill the two new sub-rows
  grid = fillrow(grid, row, endleft, middleX)
  grid = fillrow(grid, row, middleX, endright)
  return(grid)
}


# Recursively fill one column.
# Used to bootstrap the recursive area fill.
# Also used to fudge our way out of ?x2 rectangles.
fillcol = function(grid, col, endtop, endbottom) {
  if (endtop + 1 == endbottom)
    return(grid)
  # Set the dot in the middle.
  middleY = floor((endbottom - endtop) / 2 + endtop)
  grid[col, middleY] = midpoint(grid[col, endtop], grid[col, endbottom])
  # Go fill the two new sub-columns
  grid = fillcol(grid, col, endtop, middleY)
  grid = fillcol(grid, col, middleY, endbottom)
  return(grid)
}


# Recursively fill the area.
fillarea = function(grid, endtop, endbottom, endleft, endright) {
  if ((endleft + 1 == endright) && (endtop + 1 == endbottom)) {
    # This is just a 2x2 square.  Nothing to do.
  } else if (endleft + 1 == endright) {
    # This is just a 2x? rectangle.  Fill in some vertical space.
    grid = fillcol(grid, endright, endtop, endbottom)
  } else if (endtop + 1 == endbottom) {
    # This is just a ?x2 rectangle.  Fill in some horizontal space.
    grid = fillrow(grid, endbottom, endleft, endright)
  } else {
    # Wide open space; something to sink our recursive teeth into...
    # Set the dot half way along the bottom row.
    middleX = floor((endright - endleft) / 2 + endleft)
    grid[middleX, endbottom] = midpoint(grid[endleft, endbottom], grid[endright, endbottom])

    # Set the dot half way along the right column.
    middleY = floor((endbottom - endtop) / 2 + endtop)
    grid[endright, middleY] = midpoint(grid[endright, endtop], grid[endright, endbottom])

    # Set the dot in the middle (midpoint of two midpoints).
    centre1 = midpoint(grid[middleX, endtop], grid[middleX, endbottom])
    centre2 = midpoint(grid[endright, middleY], grid[endleft, middleY])
    grid[middleX, middleY] = midpoint(centre1, centre2)

    # Go fill the four new quadrants.
    grid = fillarea(grid, endtop, middleY, endleft, middleX)
    grid = fillarea(grid, middleY, endbottom, endleft, middleX)
    grid = fillarea(grid, endtop, middleY, middleX, endright)
    grid = fillarea(grid, middleY, endbottom, middleX, endright)
  }
  return(grid)
}


# The grid of points that make up the image.
grid = array(0, dim=c(cols, rows))

# Flip a coin to determine which diagonally opposite corners get the master colours.
if (runif(1) < 0.5) {
  grid[1, 1] = 0
  grid[cols, rows] = 1
  grid[cols, 1] = runif(1)
  grid[1, rows] = runif(1)
} else {
  grid[1, rows] = 0
  grid[cols, 1] = 1
  grid[1, 1] = runif(1)
  grid[cols, rows] = runif(1)
}

# Draw the top row and left column.
grid = fillrow(grid, 1, 1, cols)
grid = fillcol(grid, 1, 1, rows)

# Now we have the top edge, the left edge, and the bottom/right dot.
# We are all setup to fill the remaining area.
grid = fillarea(grid, 1, rows, 1, cols)

# RGB colour declarations for the master colours
while (TRUE) {
  c1 = runif(3)
  c2 = runif(3)
  # Keep looping until you get dissimilar colours.
  if ((abs(c1[1] - c2[1]) + abs(c1[2] - c2[2]) + abs(c1[3] - c2[3])) > 1) {
    break
  }
}
rgb.palette = colorRampPalette(c(rgb(c1[1], c1[2], c1[3]), rgb(c2[1], c2[2], c2[3])))

# Output the image
image(grid, col=rgb.palette(255), xaxt="n", yaxt="n")

# Add some text.
text(1, 0, "http://neil.fraser.name/", adj=c(0,0), srt=90)