Little UI for compass-and-straightedge constructions using https://love2d.org

love-geometry.lua

-- To run:
--   Download LÖVE from https://love2d.org
--   Download this file to a directory and rename it to `main.lua`
--   Run `love .` from that directory. (Replace 'love' with whatever the name of your LÖVE download is.)

function love.load()
  -- maximize window
  love.window.setMode(0, 0)
  local width, height, flags = love.window.getMode()
  -- shrink slightly to account for window decoration
  width = width-100
  height = height-100
  love.window.setMode(width, height)
  love.window.setTitle('Love Geometry')
  local status_height = 20
  UI = {
    x=5,y=5, w=width-10,h=100,                              -- menu area
    status_height=status_height,
    x2=5,y2=110, w2=width-10, h2=height-status_height-115,  -- shapes area
    -- top-left coords for widgets on screen
    colorx=25,colory=25,       -- toggle between black and red
    pointx=100,pointy=25,      -- point tool
    linex=175,liney=25,        -- line tool
    radiusx=250,radiusy=25,    -- set radius of compass tool
    compassx=325,compassy=25,  -- compass tool
  }
  mouse = {x=0,y=0}
  shapes_committed = {}
  current_mode = 'line'  -- valid modes: dot, line, radius, center, arcbegin, arcend
  current_red = 0  -- red component of current color (green and blue are always 0)
  current_radius = 100
  current_end_angle = nil
  pending = {}
end

function love.mousepressed(x, y, button)
  if button == 1 then
    if x>UI.colorx and x<UI.colorx+50 and y>UI.colory and y<UI.colory+50 then current_red = 1-current_red end
    if x>UI.pointx and x<UI.pointx+50 and y>UI.pointy and y<UI.pointy+50 then current_mode = 'point' end
    if x>UI.linex and x<UI.linex+50 and y>UI.liney and y<UI.liney+50 then current_mode = 'line' end
    if x>UI.radiusx and x<UI.radiusx+50 and y>UI.radiusy and y<UI.radiusy+50 then current_mode = 'radius' end
    if x>UI.compassx and x<UI.compassx+50 and y>UI.compassy and y<UI.compassy+50 then current_mode = 'center' end
    if x>UI.x2 and x<UI.x2+UI.w2 and y>UI.y2 and y<UI.y2+UI.h2 then
      if current_mode == 'point' then
        table.insert(shapes_committed, {shape='point', x=x, y=y, R=current_red})
      elseif current_mode == 'line' then
        pending = {shape = 'line', x1=x,y1=y, R=current_red}
      elseif current_mode == 'radius' then
        pending = {shape = 'radius', x1=x,y1=y}
      elseif current_mode == 'center' then
        table.insert(shapes_committed, {shape='point', x=x, y=y, R=current_red})
        pending = {shape='arc', cx=x,cy=y, r=current_radius, R=current_red}
        current_mode = 'arcbegin'
      elseif current_mode == 'arcbegin' then
        assert(pending.shape == 'arc')
        pending.s = angle(pending.cx,pending.cy, x,y)
        current_mode = 'arcend'
      end
    end
  end
end

function love.mousereleased(x,y, button)
  if x>UI.x2 and x<UI.x2+UI.w2 and y>UI.y2 and y<UI.y2+UI.h2 then
    if pending.shape == 'line' then
      pending.x2 = x
      pending.y2 = y
      table.insert(shapes_committed, pending)
      pending = {}
    elseif current_mode == 'radius' then
      -- radius widget doesn't draw anything
      current_radius = math.dist(pending.x1,pending.y1, x,y)
      pending = {}
      current_end_angle = nil
    elseif current_mode == 'arcend' then
      pending.e = current_end_angle
      table.insert(shapes_committed, pending)
      current_mode = 'center'
      pending = {}
      current_end_angle = nil
    end
  end
end

function love.update()
  mouse.x = love.mouse.getX()
  mouse.y = love.mouse.getY()
end

function love.draw()
  draw_shapes()
  draw_menu()
end

function draw_menu()
  love.graphics.setColor(0.2, 0.2, 0.2)
  love.graphics.rectangle('fill', UI.x,UI.y, UI.w,UI.h)
  local width, height, flags = love.window.getMode()
  love.graphics.setColor(1, 1, 1)
  love.graphics.print(mouse.x, 5, height-UI.status_height)
  love.graphics.print("|", 35,height-UI.status_height)
  love.graphics.print(mouse.y, 45, height-UI.status_height)

  love.graphics.setColor(current_red, 0, 0)
  love.graphics.rectangle('fill', UI.colorx,UI.colory, 50,50)

  if current_mode == 'point' then
    love.graphics.setColor(1, 1, 1)
    love.graphics.rectangle('fill', UI.pointx,UI.pointy, 50,50)
    love.graphics.setColor(current_red, 0, 0)
    love.graphics.circle('fill', UI.pointx+25,UI.pointy+25, 3)
  else
    love.graphics.setColor(0.75, 0.75, 0.75)
    love.graphics.rectangle('fill', UI.pointx,UI.pointy, 50,50)
    love.graphics.setColor(0, 0, 0)
    love.graphics.circle('fill', UI.pointx+25,UI.pointy+25, 3)
  end

  if current_mode == 'line' then
    love.graphics.setColor(1, 1, 1)
    love.graphics.rectangle('fill', UI.linex,UI.liney, 50,50)
    love.graphics.setColor(current_red, 0, 0)
    love.graphics.line(UI.linex+5,UI.liney, UI.linex+45,UI.liney+50)
  else
    love.graphics.setColor(0.75, 0.75, 0.75)
    love.graphics.rectangle('fill', UI.linex,UI.liney, 50,50)
    love.graphics.setColor(0, 0, 0)
    love.graphics.line(UI.linex+5,UI.liney, UI.linex+45,UI.liney+50)
  end

  if current_mode == 'radius' then
    love.graphics.setColor(1, 1, 1)
    love.graphics.rectangle('fill', UI.radiusx,UI.radiusy, 50,50)
    love.graphics.setColor(current_red, 0, 0)
    love.graphics.circle('fill', UI.radiusx+10,UI.radiusy+25, 3)
    love.graphics.line(UI.radiusx+10,UI.radiusy+25, UI.radiusx+40,UI.radiusy+25)
    love.graphics.circle('fill', UI.radiusx+40,UI.radiusy+25, 3)
    love.graphics.setColor(0.5, 0.5, 0.5)
    love.graphics.arc('line', 'open', UI.radiusx+10,UI.radiusy+25, 30, 1/2,-1/2)
  else
    love.graphics.setColor(0.75, 0.75, 0.75)
    love.graphics.rectangle('fill', UI.radiusx,UI.radiusy, 50,50)
    love.graphics.setColor(0, 0, 0)
    love.graphics.circle('fill', UI.radiusx+10,UI.radiusy+25, 3)
    love.graphics.line(UI.radiusx+10,UI.radiusy+25, UI.radiusx+40,UI.radiusy+25)
    love.graphics.circle('fill', UI.radiusx+40,UI.radiusy+25, 3)
    love.graphics.setColor(0.5, 0.5, 0.5)
    love.graphics.arc('line', 'open', UI.radiusx+10,UI.radiusy+25, 30, 1/2,-1/2)
  end

  if current_mode == 'center' or current_mode == 'arcbegin' then
    love.graphics.setColor(1, 1, 1)
    love.graphics.rectangle('fill', UI.compassx, UI.compassy, 50,50)
    love.graphics.setColor(0.5, 0.5, 0.5)
    love.graphics.line(UI.compassx+10,UI.compassy+25, UI.compassx+40,UI.compassy+25)
    love.graphics.setColor(current_red, 0, 0)
    love.graphics.arc('line', 'open', UI.compassx+10,UI.compassy+25, 30, 1/2,-1/2)
  else
    love.graphics.setColor(0.75, 0.75, 0.75)
    love.graphics.rectangle('fill', UI.compassx, UI.compassy, 50,50)
    love.graphics.setColor(0.5, 0.5, 0.5)
    love.graphics.line(UI.compassx+10,UI.compassy+25, UI.compassx+40,UI.compassy+25)
    love.graphics.setColor(0, 0, 0)
    love.graphics.arc('line', 'open', UI.compassx+10,UI.compassy+25, 30, 1/2,-1/2)
  end
end

function draw_shapes()
  love.graphics.setColor(1,1,1)
  love.graphics.rectangle('fill', UI.x2,UI.y2, UI.w2,UI.h2)

  for i, v in ipairs(shapes_committed) do
    love.graphics.setColor(v.R, 0, 0)
    if v.shape == 'line' then
      love.graphics.line(v.x1,v.y1, v.x2,v.y2)
    elseif v.shape == 'point' then
      love.graphics.circle('fill', v.x,v.y, 3)
    elseif v.shape == 'arc' then
      love.graphics.arc('line', 'open', v.cx,v.cy, v.r, v.s,v.e, 360)
    end
  end

  if pending.shape == 'arc' then
    love.graphics.setColor(0.75, 0.75, 0.75)
    love.graphics.circle('line', pending.cx,pending.cy, pending.r)
  end

  if love.mouse.isDown('1') then
    if pending.shape == 'line' then
      love.graphics.setColor(pending.R, 0, 0)
      love.graphics.line(pending.x1,pending.y1, mouse.x,mouse.y)
    elseif pending.shape == 'radius' then
      love.graphics.setColor(0.75, 0.75, 0.75)
      love.graphics.line(pending.x1,pending.y1, mouse.x,mouse.y)
    elseif pending.shape == 'arc' then
      if pending.s then
        current_end_angle = angle_with_hint(pending.cx,pending.cy, mouse.x,mouse.y, current_end_angle)
        love.graphics.setColor(pending.R, 0, 0)
        love.graphics.arc('line', 'open', pending.cx,pending.cy, pending.r, pending.s, current_end_angle, 360)
      end
    end
  end
end

function angle_with_hint(x1, y1, x2, y2, hint)
  local result = angle(x1,y1, x2,y2)
  if hint then
    -- Smooth the discontinuity where angle goes from positive to negative.
    -- The hint is a memory of which way we drew it last time.
    while result > hint+math.pi/10 do
      result = result-math.pi*2
    end
    while result < hint-math.pi/10 do
      result = result+math.pi*2
    end
  end
  return result
end

-- result is from -π/2 to 3π/2, approximately adding math.atan2 from Lua 5.3
-- (LÖVE is Lua 5.1)
function angle(x1,y1, x2,y2)
  local result = math.atan((y2-y1)/(x2-x1))
  if x2 < x1 then
    result = result+math.pi
  end
  return result
end

function math.dist(x1,y1, x2,y2) return ((x2-x1)^2+(y2-y1)^2)^0.5 end