#Nature of code - Oscillation - Walker with Angular Motion
#**********************************************************
# Here, we will again create a Walker but this time, in the form of an "Asteroids" spaceship.
# we will no longer use Perlin Noise to generate direction and movement. Instead we will increase/decrease the angle by keypress (left/right)
# As a fun adittion we also will adapt the speed by keypress (up/down) but the rocketship cannot exceed a speedlimit or go backward
# 
#Setup
gosub ScreenSetup
gosub ObjectSetup
gosub KeyMapping

#Draw
while 1
    gosub Steering
    gosub Update
    gosub CheckEdges
    gosub Show
    refresh
    pause 0.002
end while


#Subroutines
#**********************
ScreenSetup:
  Fastgraphics 	# write to video buffer.
  global setseed
  setSeed=0		# initialize random number generator
  t=0
  width=600
  height=600 		# good practice to put every constant in a variable.
  graphsize width,height 
  color black
  rect(0, 0, width-1, height-1)
  refresh
return

ObjectSetup:  
  #set up the rocketship's initial state
  pos = {width/2, height/2} 	# initial position of the rocketship 
  mass = 1
  radius= 20
  Angle = pi # starting angle
  incSpeed =1
return

KeyMapping:
  ar_down=16777237
  ar_up=16777235
  ar_left=16777234
  ar_right=16777236
return

Steering:
  # change the angle by an increment determined by keypress and cap the speed
  if keypressed(ar_down) then
	incSpeed = incSpeed-0.1
	if incSpeed < 0 then incSpeed = 0
  else
	if keypressed(ar_up) then
			incSpeed = incSpeed + 0.1
			if incSpeed > 8 then incSpeed = 8
    endif
  endif     # change the angle by an increment determined by keypress
  if keypressed(ar_left) then
    incAngle = -0.05
  else
	if keypressed(ar_right) then
	  incAngle = 0.05
    else
      incAngle = 0
    endif
  endif 
  Angle = Angle + incAngle
return 

Update:  
    #using the angle, we calculate the new velocity
    vel = {cos(Angle)*incSpeed,sin(Angle)*incSpeed} 
    pos[0] = pos[0] - vel[0]
    pos[1] = pos[1] - vel[1]
return

Show:
    #blank the canvas
    color rgb(0,0,0)
    rect(0, 0, width-1, height-1)    
    # draw the rocketship.
    # we want to rotate around the middle of the rocketship, so we shift the drawing of the ship half a radius back
    middle = {pos[0] - cos(Angle)*radius/2, pos[1] - sin(Angle)*radius/2}
    color white
	line (middle[0], middle[1], middle[0] + cos(Angle-0.3)*radius, middle[1] + sin(Angle-0.3)*radius)
	line (middle[0], middle[1], middle[0] + cos(Angle+0.3)*radius, middle[1] + sin(Angle+0.3)*radius)
	line (middle[0] + cos(Angle+0.3)*radius, middle[1] + sin(Angle+0.3)*radius, middle[0] + cos(Angle-0.3)*radius, middle[1] + sin(Angle-0.3)*radius)     
return

CheckEdges:
    # we constrain the Walker to the canvas
    if pos[0] > width then pos[0] = 0 
    if pos[0] < 0 then pos[0] = width
    if pos[1] > height then pos[1] = 0 
    if pos[1] < 0 then pos[1] = height 
return