Glue Bonus

In this part I want to implement a "glue" bonus: when it's on, the ball doesn't rebound from the platform, but sticks to it until the player presses a launch button.

First it is necessary to add recognition of the "glue" bonus type in the collision detection code.

function bonuses.bonus_collected( i, bonus, ball, platform )
   .....
   elseif bonuses.is_glue( bonus ) then
      platform.react_on_glue_bonus()
   end
   .....
end

function bonuses.is_glue( single_bonus )
   local col = single_bonus.bonustype % 10
   return ( col == 2 )
end

When a "glue" bonus is caught, platform.glued flag is raised and the platform tile is changed to indicate the change visually.

function platform.react_on_glue_bonus()
   platform.glued = true
   if platform.size == "small" then
      platform.quad = love.graphics.newQuad(
         platform.small_tile_x_pos + platfrom.glued_x_pos_shift,
         platform.small_tile_y_pos,
         platform.small_tile_width,
         platform.small_tile_height,
         platform.tileset_width,
         platform.tileset_height )
   elseif platform.size == "norm" then
      platform.quad = love.graphics.newQuad(
         platform.norm_tile_x_pos + platfrom.glued_x_pos_shift,
         platform.norm_tile_y_pos,
         platform.norm_tile_width,
         platform.norm_tile_height,
         platform.tileset_width,
         platform.tileset_height )
   elseif platform.size == "large" then
      platform.quad = love.graphics.newQuad(
         platform.large_tile_x_pos + platfrom.glued_x_pos_shift,
         platform.large_tile_y_pos,
         platform.large_tile_width,
         platform.large_tile_height,
         platform.tileset_width,
         platform.tileset_height )
   end   
end

Ball-platform collision depends on the value of the glued flag.

function ball.platform_rebound( shift_ball, platform )
   ball.increase_collision_counter()
   ball.increase_speed_after_collision()
   if not platform.glued then
      ball.bounce_from_sphere( shift_ball, platform )
   else
      ball.stuck_to_platform = true
      local actual_shift = ball.determine_actual_shift( shift_ball )
      ball.position = ball.position + actual_shift
      ball.platform_launch_speed_magnitude = ball.speed:len()
      ball.compute_ball_platform_separation( platform )
   end
end

function ball.compute_ball_platform_separation( platform )
   local platform_center = vector(
      platform.position.x + platform.width / 2,
      platform.position.y + platform.height / 2 )
   local ball_center = ball.position:clone()
   ball.separation_from_platform_center =
      ball_center - platform_center
   print( ball.separation_from_platform_center )   
end

The ball.launch_from_platform procedure also changes:

function ball.launch_from_platform()
   if ball.stuck_to_platform then
      ball.stuck_to_platform = false      
      local platform_halfwidth = 70       --(*1)
      local launch_direction = vector(
         ball.separation_from_platform_center.x / platform_halfwidth, -1 )
      ball.speed = launch_direction / launch_direction:len() *
         ball.platform_launch_speed_magnitude
   end
end

(*1): Half-width of the big platform is used, since it provides more diverse angles.

The first launch parameters also should be updated.

local initial_launch_speed_magnitude = 300
ball.platform_launch_speed_magnitude = initial_launch_speed_magnitude
local ball_platform_initial_separation = vector(
   ball_x_shift, -1 * platform_height / 2 - ball.radius - 1 )
ball.separation_from_platform_center = ball_platform_initial_separation 

The glued effect is removed if any other bonus (except another "glue" bonus) is caught.

function bonuses.bonus_collected( i, bonus, ball, platform )
   if not bonuses.is_glue( bonus ) then
      platform.remove_glued_effect()
      ball.launch_from_platform()
   end
   .....
   table.remove( bonuses.current_level_bonuses, i )
end

function platform.remove_glued_effect()
   if platform.glued then
      platform.glued = false
      if platform.size == "small" then
         platform.quad = love.graphics.newQuad(
            platform.small_tile_x_pos,
            platform.small_tile_y_pos,
            platform.small_tile_width,
            platform.small_tile_height,
            platform.tileset_width,
            platform.tileset_height )
      elseif platform.size == "norm" then
         platform.quad = love.graphics.newQuad(
            platform.norm_tile_x_pos,
            platform.norm_tile_y_pos,
            platform.norm_tile_width,
            platform.norm_tile_height,
            platform.tileset_width,
            platform.tileset_height )
      elseif platform.size == "large" then
         platform.quad = love.graphics.newQuad(
            platform.large_tile_x_pos,
            platform.large_tile_y_pos,
            platform.large_tile_width,
            platform.large_tile_height,
            platform.tileset_width,
            platform.tileset_height )
      end
   end
end

The effect is also removed if the ball is lost, or the next level is reached.

function game.enter( prev_state, ... )
   .....
   if args and args.current_level then
      .....
      ball.reposition()
      platform.remove_bonuses_effects()
   end      
end

function game.check_no_more_balls( ball, lives_display )
   if ball.escaped_screen then
         .....
         ball.reposition()
         platform.remove_bonuses_effects()
         .....
   end
end

function platform.remove_bonuses_effects()
   platform.remove_glued_effect()
   platform.reset_size_to_norm()
end

function ball.reposition()
   ball.escaped_screen = false
   ball.collision_counter = 0
   ball.stuck_to_platform = true
   ball.platform_launch_speed_magnitude = initial_launch_speed_magnitude
   ball.separation_from_platform_center = ball_platform_initial_separation 
end