#Nature of code - Fire Simulation
#***********************************************************************
# The Nature of Code chapter has a piece on image textures and blending. It can do that because it has functions like tint (which tints an image using a color) and blendmodes like additive blending. BASIC-256 can load images but can't change the tint and although there are no specific blend modes, using alpha allows you to do additive blending)
# So, while we still want a smoke/fire simulation, we'll take it step by step and start by creating our own fuzzy circle/smoke particle from scratch
#

  gosub ScreenSetup
  gosub FuzzyDeclaration
while true  
  gosub Show 
end while  

ScreenSetup:
  Fastgraphics 	# write to video buffer.
  width=200
  height=200 		# good practice to put every constant in a variable.
  graphsize width,height 
  color black
  rect(0, 0, width, height)
  refresh
return

FuzzyDeclaration:
  # originpoint of the fuzzy circle
  center_x= width/2
  center_y = height/2
  # color of the fuzzy circle (white)
  col = 255
  # Radius of the Fuzzy circle
  radius = 30
  # Decrease in the circle diameter. Also influences alpha
  stepsize = 2
  #alpha factor
  alpha = 30/2
  # how far it moves from the center to the left and to theright
  move_x=50
  inc = 2
return

  
Show:  
  # Now we show the fuzzy circle by drawing ever smaller circles with the same small alpha and then move it from left to right and back via the move_x parameter
  # oscillate between 30 left and right of the centre
  for loc_x = center_x - move_x to center_x + move_x step inc
    # we'll make  circles decreasing with 'stepsize' and overlaying each circle with the next smaller one. This causes additive blending of the circles
    for x= radius to 1 step -stepsize
      color rgb(col,col,col,alpha)
      circle (loc_x,center_y,x)
    next x   
    refresh
    pause 0.02
    color black
    rect(0, 0, width, height)
  next loc_x  
  move_x=-move_x
  inc = -inc
return