Bonus effects

In this part I want to implement four bonus effects: accelerate/decelerate the ball, and increase/decrease the platform size.

A bonus effect is applied when the player catches a falling bonus with the platform, i.e. on bonus-platform collision. So, in the first place it is necessary to detect such types of collisions.

function collisions.resolve_collisions( ball, platform,
                                        walls, bricks, bonuses )
   .....
   collisions.platform_bonuses_collision( platform, bonuses, ball )       --(*1)
end

function collisions.platform_bonuses_collision( platform, bonuses, ball )
   local overlap
   local b = { x = platform.position.x,
               y = platform.position.y,
               width = platform.width,
               height = platform.height }
   for i, bonus in pairs( bonuses.current_level_bonuses ) do
      local a = { x = bonus.position.x - bonuses.radius,
                  y = bonus.position.y - bonuses.radius,
                  width = 2 * bonuses.radius,
                  height = 2 * bonuses.radius }      
      overlap = collisions.check_rectangles_overlap( a, b )
      if overlap then
         bonuses.bonus_collected( i, bonus, ball, platform )             --(*2)
      end
   end
end

(*1): Check for bonus-platform collisions is inserted along with the other collisions checks.
(*2): A bonus-platform overlap is checked similarly to the platform-ball. If an overlap is detected, a function bonuses.bonus_collected that applies bonus effect is called.

Bonustypes from left to right: 11 - slowdown, 12 - glue, 13 - increase, 14 - new ball, 15 - accelerate, 16 - decrease, 17 - next level , 18 - new life.

To apply bonus effect, first it is necessary to determine the bonus type. The procedure is analogous to the bricks. Slowdown and accelerate are 11 and 15, increase and decrease are 13 and 16. The bonus has to be removed from the game after it's effect is applied.

function bonuses.bonus_collected( i, bonus, ball, platform )
   if bonuses.is_slowdown( bonus ) then
      .....
   elseif bonuses.is_accelerate( bonus ) then
      .....
   elseif bonuses.is_increase( bonus ) then
      .....
   elseif bonuses.is_decrease( bonus ) then
      .....
   end
   table.remove( bonuses.current_level_bonuses, i )           --(*1)
end

function bonuses.is_slowdown( single_bonus )
   local col = single_bonus.bonustype % 10
   return ( col == 1 )
end

function bonuses.is_accelerate( single_bonus )
   local col = single_bonus.bonustype % 10
   return ( col == 5 )
end

function bonuses.is_increase( single_bonus )
   local col = single_bonus.bonustype % 10
   return ( col == 3 )
end

function bonuses.is_decrease( single_bonus )
   local col = single_bonus.bonustype % 10
   return ( col == 6 )
end

(*1): Remove the bonus from the game.

To accelerate or decelerate the ball, it is necessary to insert a call to the appropriate functions in the ball table. For this, bonuses.bonus_collected needs an access to the ball table. It becomes necessary to pass the ball as an argument all the way down from the collisions.platform_bonuses_collision call.

function bonuses.bonus_collected( i, bonus, ball, platform )
   if bonuses.is_slowdown( bonus ) then
      ball.react_on_slow_down_bonus()
   elseif bonuses.is_accelerate( bonus ) then
      ball.react_on_accelerate_bonus()
   elseif 
   .....
end

function ball.react_on_slow_down_bonus()
   local slowdown = 0.7
   ball.speed = ball.speed * slowdown         --(*1)
end

function ball.react_on_accelerate_bonus()
   local accelerate = 1.3
   ball.speed = ball.speed * accelerate       --(*1)
end

(*1): Acceleration or deceleration of the ball simply changes it's speed. The actual way it is done can be adjusted; I simply scale it by some constant.

4. Platfrom increase-decrease

function bonuses.bonus_collected( i, bonus, ball, platform )
   if 
      .....
   elseif bonuses.is_increase( bonus ) then
      platform.react_on_decrease_bonus()
   elseif bonuses.is_decrease( bonus ) then
      platform.react_on_increase_bonus()
   end
   table.remove( bonuses.current_level_bonuses, i )
end

...
platform.width = platform.norm_tile_width
platform.height = platform.norm_tile_height
platform.size = "norm"

function platform.react_on_decrease_bonus()
   if platform.size == "norm" then
      platform.width = platform.small_tile_width
      platform.height = platform.small_tile_height
      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 )
      platform.size = "small"
   elseif platform.size == "large" then
      platform.width = platform.norm_tile_width
      platform.height = platform.norm_tile_height
      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 )
      platform.size = "norm"     
   end
end

function platform.react_on_increase_bonus()
   if platform.size == "small" then
      platform.width = platform.norm_tile_width
      platform.height = platform.norm_tile_height
      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 )
      platform.size = "norm"
   elseif platform.size == "norm" then
      platform.width = platform.large_tile_width
      platform.height = platform.large_tile_height
      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 )
      platform.size = "large"
   end
end

5. Care should be taken regarding platform sizes if next level is reached or the ball is lost.

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


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

function platform.reset_size_to_norm()
   platform.width = platform.norm_tile_width
   platform.height = platform.norm_tile_height
   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 )
   platform.size = "norm"   
end