22. 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.
本节要实现“粘性（glue）”奖励：激活后，球不会从平台反弹，而是粘在平台上，直到玩家按下发射按钮。
First it is necessary to add recognition of the "glue" bonus type in the collision detection code.
首先要在碰撞检测代码中加入对 “glue” 奖励类型的识别。
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 )
endWhen a "glue" bonus is caught, platform.glued flag is raised and the platform tile is changed to indicate the change visually.
当吃到 “glue” 奖励时，设置 platform.glued 标志，并切换平台 tile 来显示视觉变化。
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
endBall-platform collision depends on the value of the glued flag.
球-平台碰撞的处理取决于 glued 标志的值。
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() --(*1)
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(*1): On ball collision with the "glued" platform, ball speed magnitude is memorized and used later, when the ball is launched from the platform.
(*1)：当球撞到“粘性”平台时，会记录当前球速大小，之后球从平台发射时会用到它。
The ball.launch_from_platform procedure is changed. Launch speed magnitude equals to the speed magnitude before the collision and launch angle is determined from the distance between the ball and platform centers.
ball.launch_from_platform 需要修改。发射速度大小等于碰撞前的速度大小，而发射角度由球心与平台中心的相对位置决定。
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.
(*1)：使用大平台的半宽度，因为这样能产生更多样的角度。
For ball.launch_from_platform to be applicable on the start of the level (i.e. when the ball is stuck to the platform, but the platform is not "glued"), it is necessary to initialize ball.platform_launch_speed_magnitude and ball.separation_from_platform_center with some initial values.
为了让 ball.launch_from_platform 在关卡开始时也能使用（此时球粘在平台上，但平台并未“胶黏”），需要为 ball.platform_launch_speed_magnitude 和 ball.separation_from_platform_center 设置初始值。
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_separationThe glued effect is removed if any other bonus (except another "glue" bonus) is caught.
如果玩家吃到其它奖励（除“glue”外），粘性效果会被移除。
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
endThe effect is also removed if the ball is lost, or the next level is reached.
当球丢失或进入下一关时，也要移除该效果。
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