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## Turtle Graphics
## code by Linlin Yan <linlin.yan@cos.name>
## URL: https://d.cosx.org/d/15876
turtle_x <- 0
turtle_y <- 0
turtle_direction <- 0
turtle_color <- "white"
turtle_drawing <- TRUE
turtle_init <- function(width = 100, height = 100,
mar = rep(0, 4), bg = "black", ...) {
par(mar = mar)
par(bg = bg)
plot(c(-width, width), c(-height, height), type = "n", xlab = "",
ylab = "", axes = FALSE, ...)
turtle_x <<- 0
turtle_y <<- 0
turtle_direction <<- 0
}
turtle_goto <- function(x, y) {
if (turtle_drawing) {
segments(turtle_x, turtle_y, x, y, col = turtle_color)
}
turtle_x <<- x
turtle_y <<- y
}
turtle_pen_up <- function() {
turtle_drawing <<- FALSE
}
turtle_pen_down <- function() {
turtle_drawing <<- TRUE
}
turtle_forward <- function(distance) {
x <- turtle_x + distance * cos(turtle_direction * pi/180)
y <- turtle_y + distance * sin(turtle_direction * pi/180)
turtle_goto(x, y)
}
turtle_turn_left <- function(degree) {
turtle_direction <<- (turtle_direction + degree)%%360
}
turtle_turn_right <- function(degree) {
turtle_direction <<- (turtle_direction - degree)%%360
}
turtle_set_color <- function(col) {
turtle_color <<- col
}
turtle_demo <- function() {
turtle_init()
for (i in 1:4) {
turtle_forward(50)
turtle_turn_right(90)
}
readline("Press <Enter> to continue...")
turtle_init()
turtle_set_color("blue")
for (i in 1:16) {
for (j in 1:4) {
turtle_forward(10)
turtle_turn_right(90)
}
turtle_pen_up()
turtle_forward(15)
turtle_pen_down()
if (i%%4 == 0) {
turtle_turn_left(90)
}
}
readline("Press <Enter> to continue...")
turtle_init()
turtle_set_color("gold")
for (i in 1:5) {
turtle_forward(100)
turtle_turn_right(144)
}
readline("Press <Enter> to continue...")
turtle_init()
turtle_set_color("green")
size <- 0.01
for (i in 1:720) {
turtle_forward(size)
turtle_turn_right(3)
size <- size * 1.01
}
readline("Press <Enter> to continue...")
turtle_init()
turtle_set_color("red")
for (i in 1:20) {
turtle_forward(50)
turtle_turn_right(100)
}
readline("Press <Enter> to continue...")
turtle_init()
turtle_set_color("yellow")
for (i in 1:36) {
for (j in 1:4) {
turtle_forward(5)
turtle_turn_right(90)
}
turtle_turn_right(10)
turtle_forward(15)
for (j in 1:4) {
turtle_forward(10)
turtle_turn_right(90)
}
turtle_turn_right(10)
}
readline("Press <Enter> to continue...")
turtle_init()
for (i in 1:25) {
turtle_set_color(rgb(10 * i, 5 * i, 255 - (10 * i), maxColorValue = 255))
for (j in 1:9) {
turtle_forward(100)
turtle_turn_right(160)
}
turtle_turn_right(24)
}
}
turtle_demo()
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