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scorched.rb
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scorched.rb
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# Basic Scorched Earth clone.
# Copyright (C) 2012 Rich Lane
# This code is released under the BSD two-clause license.
#
# Use the arrow keys to adjust the angle and power of the tank gun. Hit
# space to fire. The last tank alive wins!
#
# TODO Collide bullets directly with players.
# TODO Fall damage.
NUM_PLAYERS = 3
G = 0.1 # Acceleration due to gravity (pixels/frame).
MAX_POWER = 300
STATUS_SCREEN_HEIGHT = 75
MAX_WIND = 2
BULLET_DRAG = 0.002
def setup
$ticks = 0
$last_fire_tick = 0
setup_terrain()
setup_players()
setup_bullets()
setup_explosions()
setup_wind()
end
# Generate terrain using the midpoint displacement algorithm.
def setup_terrain
# Tunables.
initial_height = SCREEN_HEIGHT-200
max_displacement = 100
displacement_growth = 0.92
iterations = 1000
# x0 and width must be integers.
lines = [ { x0: 0, width: 400, slope: -0.2 }, { x0: 400, width: 400, slope: 0.2 } ]
# For each iteration, pick a random line and split it in two. Move the
# middle point up or down by a random amount. The maximum amount it can
# be moved decreases with each iteration.
y0 = initial_height
iterations.times do
j = random(0, lines.length).to_i
lA = lines[j]
y1 = y0 + lA[:width]*lA[:slope]
widthA = (lA[:width]/2).ceil
widthB = (lA[:width]/2).floor
if widthB == 0 then
# skip
else
midy = y0+lA[:width]*lA[:slope]/2
dy = random(-max_displacement, max_displacement)
# y = y0 + slope*x
# slope = (y-y0)/x
slopeA = (midy+dy-y0)/widthA
slopeB = (y1-midy-dy)/widthB
lB = { x0: lA[:x0]+widthA, width: widthB, slope: slopeB }
lines.push(lB)
lA[:width] = widthA
lA[:slope] = slopeA
max_displacement = max_displacement * displacement_growth
end
y0 = y1
end
# Sort the lines by x0.
lines = lines.sort { |a,b| a[:x0] <=> b[:x0] }
# Build the terrain height-map from the lines.
$terrain = {}
y0 = initial_height
lines.each do |l|
((l[:x0])...(l[:x0]+l[:width])).each do |x|
$terrain[x] = y0 + (x-l[:x0])*l[:slope]
end
y0 = y0 + l[:width]*l[:slope]
end
end
def setup_players
$players = {}
$live_players = NUM_PLAYERS
NUM_PLAYERS.times do |i|
x = random(10, SCREEN_WIDTH-10).to_i
player = {
x: x,
y: $terrain[x],
angle: 90,
power: 100,
health: 100,
r: 255,
g: 0,
b: 0,
}
((player[:x] - 8)..(player[:x] + 8)).each do |x|
if $terrain[x] >= player[:y] then
$terrain[x] = player[:y]-1
end
end
$players[i] = player
end
$current_player_index = 0
$current_player = $players[0]
end
# Pick a new non-dead player
def next_player
if $live_players == 0 then return end
$current_player_index = ($current_player_index + 1) % NUM_PLAYERS
$current_player = $players[$current_player_index]
if $current_player_index == nil or $current_player[:health] == 0 then
return next_player()
end
end
# Choose a color representing the player's status (current, dead, alive)
def player_status_color(player)
if player == $current_player then
color(220, 220, 220, 255)
elsif player[:health] == 0 then
color(100, 0, 0, 255)
else
color(127, 127, 127, 255)
end
end
def setup_bullets
$bullets = []
end
def setup_explosions
$explosions = []
end
def setup_wind
$wind = random(-MAX_WIND, MAX_WIND)
end
# If there is only one live player left return its index. Otherwise return nil.
def find_victor
winner_index = nil
$players.each do |i,player|
if player[:health] > 0 then
if winner_index then
return nil
else
winner_index = i
end
end
end
return winner_index
end
def draw
draw_sky()
draw_terrain()
draw_players()
draw_bullets()
draw_explosions()
draw_status()
draw_wind()
end
def handle_input
ks = keys
if ks.member?('left') then
$current_player[:angle] = $current_player[:angle] + 1
end
if ks.member?('right') then
$current_player[:angle] = $current_player[:angle] - 1
end
if ks.member?('up') and $current_player[:power] < MAX_POWER then
$current_player[:power] = $current_player[:power] + 1
end
if ks.member?('down') and $current_player[:power] > 0 then
$current_player[:power] = $current_player[:power] - 1
end
if ks.member?('space') and
$bullets.size == 0 and
$last_fire_tick < $ticks - 16 then
fire()
$last_fire_tick = $ticks
end
if ks.member?('return') and
$bullets.size == 0 and
$last_fire_tick < $ticks - 16 then
fire_secret()
$last_fire_tick = $ticks
end
end
def fire
player = $current_player
speed = player[:power]/10
bullet = {
player: player,
x: player[:x],
y: player[:y],
vx: cos(player[:angle])*speed,
vy: -sin(player[:angle])*speed,
exp_radius: 30,
exp_damage: 100,
}
$bullets.push(bullet)
end
def fire_secret
player = $current_player
speed = player[:power]/10
10.times do
a = player[:angle] + random(-3, 3)
bullet = {
player: player,
x: player[:x],
y: player[:y],
vx: cos(a)*speed,
vy: -sin(a)*speed,
exp_radius: 10,
exp_damage: 40,
}
$bullets.push(bullet)
end
end
# Drag increases with the square of the difference in velocity between
# the object and the air. Returns the acceleration due to drag.
def bullet_drag(v)
a = v**2 * BULLET_DRAG
if v > 0 then a = -a end # Oppose velocity.
return a
end
# Do bullet physics and check for collisions with terrain or the sides of the screen.
def tick_bullets
collided = false
$bullets.each do |bullet|
bullet[:x] = bullet[:x] + bullet[:vx]
bullet[:y] = bullet[:y] + bullet[:vy]
bullet[:vx] = bullet[:vx] + bullet_drag(bullet[:vx]-$wind)
bullet[:vy] = bullet[:vy] + bullet_drag(bullet[:vy]) + G
ix = bullet[:x].round
if ix < 0 or ix >= SCREEN_WIDTH then
bullet[:dead] = true
collided = true
elsif bullet[:y] > $terrain[ix] then
bullet[:y] = $terrain[ix]
$explosions.push({ x: bullet[:x], y: bullet[:y], r: bullet[:exp_radius], ttl: 20, lifetime: 20 })
damage_players(bullet[:x], bullet[:y], bullet[:exp_radius], bullet[:exp_damage])
deform_terrain(ix, bullet[:y], bullet[:exp_radius])
bullet[:dead] = true
collided = true
end
end
$bullets = $bullets.select { |bullet| !bullet[:dead] }
if collided
after_bullet_collision()
end
end
# Find the players in the damage radius of an explosion and reduce their health.
def damage_players(x, y, r, s)
$players.each do |i,player|
#p [:damage_players, i, player]
d = distance(x, y, player[:x], player[:y])
if player[:health] > 0 and d < r then
# Damage attenuates linearly with distance (in 2d).
e = s*(1-(d/r))
player[:health] = [player[:health] - e, 0].max
if player[:health] == 0 then
$live_players = $live_players - 1
end
end
end
end
# Remove a circular chunk of terrain.
def deform_terrain(x, y, r)
(([x-r,0].max)..([x+r,SCREEN_WIDTH-1].min)).each do |x2|
dx = x2 - x
dy = Math.sqrt(r*r - dx*dx)
ty = $terrain[x2]
missing = ty + dy - y
missing = [missing, 0].max
missing = [missing, 2*dy].min
$terrain[x2] = ty + (2*dy - missing)
end
# Drop players
$players.each do |i,player|
ty = $terrain[player[:x].floor]
if player[:y] < ty-1 then
player[:y] = ty-1
end
end
end
# If all the bullets have collided switch to the next player.
def after_bullet_collision
if $bullets.size == 0
next_player()
end
end
def draw_sky
top = STATUS_SCREEN_HEIGHT+1
alpha = $bullets.size > 0 ? 127 : 255
(top..SCREEN_HEIGHT).each do |i|
f = i.to_f/(SCREEN_HEIGHT-top)
color(30*f, 30*f, 200*f, alpha)
line(0, i, SCREEN_WIDTH-1, i)
end
end
def draw_terrain
(0...SCREEN_WIDTH).each do |i|
h = $terrain[i]
# Draw a vertical line from the bottom
color(36, 142, 36, 255)
line(i, SCREEN_HEIGHT, i, h.ceil)
# Antialias by drawing a point with transparency equal to the
# fraction of a pixel that was ignored above.
frac = h-h.ceil
if frac > 0 then
color(36, 142, 36, frac*255)
box(i, h.ceil, 1, 1)
end
end
end
def draw_players
$players.each do |i,player|
color(player[:r], player[:g], player[:b], 255)
box(player[:x]-6, player[:y], player[:x]+6, player[:y]-8, fill: true)
l = 13
line(player[:x], player[:y]-6,
player[:x] + l*cos(player[:angle]),
player[:y]-6 - l*sin(player[:angle]))
player_status_color(player)
text(player[:x]-5, player[:y]+6, i.to_s)
end
end
def draw_bullets
top = STATUS_SCREEN_HEIGHT
$bullets.each do |bullet|
if bullet[:y] > top
color(200, 200, 200, 255)
box(bullet[:x]-1, bullet[:y]-1, bullet[:x]+1, bullet[:y]+1, fill: true)
else
color(200, 200, 200, 255)
l = 5
line(bullet[:x]-l, top+l, bullet[:x], top)
line(bullet[:x]+l, top+l, bullet[:x], top)
end
end
end
def draw_explosions
$explosions.each do |exp|
color(251, 130, 48, 255)
r = exp[:r] * exp[:ttl]/exp[:lifetime]
circle(exp[:x], exp[:y], r, fill: true)
exp[:ttl] = exp[:ttl] - 1
end
$explosions = $explosions.select { |exp| exp[:ttl] > 0 }
end
def draw_status
color(0, 0, 0, 255)
box(0, 0, SCREEN_WIDTH-1, STATUS_SCREEN_HEIGHT-1, fill: true)
color(150, 150, 150, 255)
line(0, STATUS_SCREEN_HEIGHT, SCREEN_WIDTH-1, STATUS_SCREEN_HEIGHT)
x = 5
padding = 40
$players.each do |i,player|
player_status_color(player)
y = 5
dy = 17
text(x, y+0*dy, "player #{i}")
text(x, y+1*dy, "health: #{player[:health].to_i}")
text(x, y+2*dy, "angle: #{player[:angle].to_i}")
text(x, y+3*dy, "power: #{player[:power].to_i}")
x = x + 15*10 + padding
color(150, 150, 150, 255)
line(x-padding/2, 0, x-padding/2, STATUS_SCREEN_HEIGHT)
end
end
def draw_wind
color(79, 64, 19, 255)
scale = 100
cx = SCREEN_WIDTH/2
wx = cx + $wind*scale/MAX_WIND
wy = SCREEN_HEIGHT-30
text(cx-20, wy-20, "wind")
line(cx, wy+3, cx, wy-3)
dir = $wind > 0 ? 1 : -1
wsx = cx+scale*dir
line(wsx, wy+3, wsx, wy-3)
line(cx, wy, wx, wy)
line(wx, wy, wx-3*dir, wy-3)
line(wx, wy, wx-3*dir, wy+3)
end
setup
while true
$ticks = $ticks + 1
game_over = $live_players <= 1
if not game_over then
handle_input()
tick_bullets()
end
draw
if game_over then
keys
color(230, 230, 230, 255)
if $live_players == 1 then
winning_player_index = find_victor()
str = "Player #{winning_player_index} wins!"
text(SCREEN_WIDTH/2-str.length*5, SCREEN_HEIGHT/2, str)
else
text(SCREEN_WIDTH/2-5*5, SCREEN_HEIGHT/2, "Draw!")
end
end
if $ticks < 30*3 then
centerText = lambda { |y, str| text(SCREEN_WIDTH/2-str.length*5, y, str) }
color(200, 200, 200, 255-255*$ticks/90.0)
centerText[460, "Use the arrow keys to control your tank's gun."]
centerText[445, "Press the space key to fire."]
end
display
delay(30)
end