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 the program from that directory.
--     * on Linux (using the appimage binary): `chmod +x path/to/love-11.4-x86_64.AppImage; path/to/love-11.4-x86_64.AppImage .` 
--     * on Mac: `path/to/love.app/Contents/MacOS/love .`

-- maximize window
love.window.setMode(0, 0)
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')

-- the window has 3 major parts: menu, drawing area and status bar
status_height = 20
menux, menuy = 5, 5
menuw, menuh = width-10, 100
shapex, shapey = 5, 110
shapew, shapeh = width-10, height-status_height-115

-- state that affects the shape currently being drawn
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 = {}

-- shapes drawn in the past
shapes_committed = {}

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

-- ### Rendering shapes
-- This section takes current_mode largely for granted.

function draw_shapes()
  love.graphics.setColor(1,1,1)
  love.graphics.rectangle('fill', shapex,shapey, shapew,shapeh)

  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, 2)
    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, love.mouse.getX(),love.mouse.getY())
    elseif pending.shape == 'radius' then
      love.graphics.setColor(0.75, 0.75, 0.75)
      love.graphics.line(pending.x1,pending.y1, love.mouse.getX(),love.mouse.getY())
    elseif pending.shape == 'arc' then
      if pending.s then
        current_end_angle = angle_with_hint(pending.cx,pending.cy, love.mouse.getX(),love.mouse.getY(), 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

-- Summary of mouse events:
--   drawing lines: press(x1,y1) -> release(x2,y2)
--   setting radius: press -> release(radius)
--   drawing arcs: press(center), press(start_angle) -> press(end_angle)
--    (current_mode changes here from 'center' to 'arcbegin' to 'arcend')

function love.mousepressed(x, y, button)
  menu_pressed(x, y, button)
  if button == 1 then
    if x>shapex and x<shapex+shapew and y>shapey and y<shapey+shapeh 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>shapex and x<shapex+shapew and y>shapey and y<shapey+shapeh 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 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

-- ### Menu area and widgets
-- Here we update current_mode.

events = {}

function draw_menu()
  events = {}
  love.graphics.setColor(0.2, 0.2, 0.2)
  love.graphics.rectangle('fill', menux,menuy, menuw,menuh)
  local width, height, flags = love.window.getMode()
  love.graphics.setColor(1, 1, 1)
  love.graphics.print(love.mouse.getX(), 5, height-status_height)
  love.graphics.print("|", 35,height-status_height)
  love.graphics.print(love.mouse.getY(), 45, height-status_height)

  button('color', {x=25,y=25, w=50,h=50, color={current_red,0,0},
    onpress1 = function() current_red = 1 - current_red end})

  button('point', {x=100,y=25, w=50,h=50,
    color = (current_mode == 'point' and {1,1,1} or {0.75,0.75,0.75}),
    icon = function()
             love.graphics.setColor(current_mode == 'point' and current_red or 0, 0, 0)
             love.graphics.circle('fill', 100+50/2,25+50/2, 2)
           end,
    onpress1 = function() current_mode = 'point' end})

  button('line', {x=175,y=25, w=50,h=50,
    color = (current_mode == 'line' and {1,1,1} or {0.75,0.75,0.75}),
    icon = function()
             love.graphics.setColor(current_mode == 'line' and current_red or 0, 0, 0)
             love.graphics.line(175+5,25, 175+50-5,25+50)
           end,
    onpress1 = function() current_mode = 'line' end})

  button('radius', {x=250,y=25, w=50,h=50,
    color = (current_mode == 'radius' and {1,1,1} or {0.75,0.75,0.75}),
    icon = function()
             local y = 25+50/2
             love.graphics.setColor(current_mode == 'radius' and current_red or 0, 0, 0)
             love.graphics.circle('fill', 250+10,y, 2)
             love.graphics.line(250+10,y, 250+40,y)
             love.graphics.circle('fill', 250+40,y, 2)
             love.graphics.setColor(0.5, 0.5, 0.5)
             love.graphics.arc('line', 'open', 250+10,y, 30, 1/2,-1/2)
           end,
    onpress1 = function() current_mode = 'radius' end})

  local arc_pressed = one_of(current_mode, {'center', 'arcbegin', 'arcend'})
  button('arc', {x=325,y=25, w=50,h=50,
    color = (arc_pressed and {1,1,1} or {0.75,0.75,0.75}),
    icon = function()
             local y = 25+50/2
             love.graphics.setColor(0.5, 0.5, 0.5)
             love.graphics.line(325+10,y, 325+40,y)
             love.graphics.setColor(arc_pressed and current_red or 0, 0, 0)
             love.graphics.arc('line', 'open', 325+10,y, 30, 1/2,-1/2)
           end,
    onpress1 = function() current_mode = 'center' end})
end

-- draw button and queue up event handlers
function button(name, params)
  love.graphics.setColor(params.color[1], params.color[2], params.color[3])
  love.graphics.rectangle('fill', params.x,params.y, params.w,params.h)
  if params.icon then params.icon() end
  table.insert(events, params)
end

-- process button event handlers
function menu_pressed(x, y, button)
  for _,ev in ipairs(events) do
    if x>ev.x and x<ev.x+ev.w and y>ev.y and y<ev.y+ev.h then
      if ev.onpress1 and button == 1 then ev.onpress1() end
    end
  end
end

function one_of(v, t)
  for _,x in ipairs(t) do
    if v == x then return true end
  end
  return false
end