Bezier Curves

How use?

Visualize and understand how Bezier curves can be programmed

Click button A[z] or B[x] to switch between Quadratic curve and Cubic curve

Code:

-- Initial x and y
x, y = 120, 120


-- Set starter bezier
mode = 1


-- Lerp function
function lerp(x1, y1, x2, y2, t)
 local x = x1 + (x2-x1) * t
 local y = y1 + (y2-y1) * t
 return {x,y}
end


-- Quadratic bezier
function bezierQuad(x1,y1,x2,y2,x3,y3)
 
 -- Clay squares
 for i = 0,1.0001, 0.1 do
  local x = lerp(lerp(x1,y1,x2,y2,i)[1],lerp(x1,y1,x2,y2,i)[2],lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],i)[1]
  local y = lerp(lerp(x1,y1,x2,y2,i)[1],lerp(x1,y1,x2,y2,i)[2],lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],i)[2]
  line(lerp(x1,y1,x2,y2,i)[1],lerp(x1,y1,x2,y2,i)[2],lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],15)
 end
 
 -- Lines of bezier
 local xlast = x1
 local ylast = y1
 for i = 0,1.01, 0.01 do
  local x = lerp(lerp(x1,y1,x2,y2,i)[1],lerp(x1,y1,x2,y2,i)[2],lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],i)[1]
  local y = lerp(lerp(x1,y1,x2,y2,i)[1],lerp(x1,y1,x2,y2,i)[2],lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],i)[2]
  line(xlast, ylast, x, y,2)
  xlast, ylast = x, y
 end
end


-- Cubic bezier
function bezierCub(x1,y1,x2,y2,x3,y3,x4,y4)
 
 -- Clay squares
 for i = 0,1.0001, 0.1 do
  line(lerp(x1,y1,x2,y2,i)[1],lerp(x1,y1,x2,y2,i)[2],lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],15)
  line(lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],lerp(x3,y3,x4,y4,i)[1],lerp(x3,y3,x4,y4,i)[2],15)
  line(xb1, yb1, xb2, yb2, 15)
  --line(lerp(xb1,yb1,xb2,yb2,i)[1],lerp(xb1,yb1,xb2,yb2,i)[2],15)
 end
 
 -- Lines of bezier
 local xlast = x1
 local ylast = y1
 for i = 0,1.01, 0.01 do
  local xb1 = lerp(lerp(x1,y1,x2,y2,i)[1],lerp(x1,y1,x2,y2,i)[2],lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],i)[1]
  local yb1 = lerp(lerp(x1,y1,x2,y2,i)[1],lerp(x1,y1,x2,y2,i)[2],lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],i)[2]
  local xb2 = lerp(lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],lerp(x3,y3,x4,y4,i)[1],lerp(x3,y3,x4,y4,i)[2],i)[1]
  local yb2 = lerp(lerp(x2,y2,x3,y3,i)[1],lerp(x2,y2,x3,y3,i)[2],lerp(x3,y3,x4,y4,i)[1],lerp(x3,y3,x4,y4,i)[2],i)[2]
  local x = lerp(xb1, yb1, xb2, yb2, i)[1]
  local y = lerp(xb1, yb1, xb2, yb2, i)[2]
  line(xlast, ylast, x, y,2)
  xlast, ylast = x, y
 end
end


function TIC() cls()
 
 -- Set x,y of mouse
 _,_, mouseOn = mouse()
 if mouseOn then
  x,y = mouse()
  print(x..":"..y,x+20,y)
 end


 -- Drawn a quadratic bezier
 if mode == 0 then 
  bezierQuad(0, 60, x, y, 240, 60)
  -- Show point
  if mouseOn then
   circ(x,y,2,3)
  else
   print("Quadratic Bezier",10,120,13)
  end
 end
 -- Drawn a cubic bezier
 if mode == 1 then 
  bezierCub(0, 60, x/2, y, 120+x/2, 135-y, 240, 60)
  -- Show points
  if mouseOn then
   circ(x/2, y,2,3)
   circ(120+x/2, 135-y,2,3)
  else
   print("Cubic Bezier",10,120,13)
  end
 end
 
 if btn(4) then
  mode = 0
 elseif btn(5) then
  mode = 1
 end
 
end