制作一款打飞机游戏教程5：添加子弹

在上一篇中，我们设计了一个原型来测试飞船的移动和射击感觉。

我们注意到飞船在左右转向时的动画响应不一致。通过调整动画的中心值和范围，我们解决了这个问题，使得飞船在左右转向时的动画响应更加对称和一致。

为了简化代码并提高可读性，我们使用了三元运算符来替换一些冗长的if-else语句。虽然这次优化节省的不多，但它使代码更加紧凑和易于维护。

接下来，我们开始实现射击功能。首先，我们设计了一个简单的子弹精灵，并编写了代码来控制子弹的发射和移动。

我们通过在按下射击键时创建一个新的子弹对象，并将其添加到子弹数组中来实现子弹的发射。然后，在更新函数中遍历子弹数组，更新每个子弹的位置。

为了避免子弹发射过快导致的视觉混乱，我们实现了一个射击频率控制机制。通过设置子弹的发射间隔，我们可以控制子弹的发射速度，使其看起来更加合理。

为了增强游戏的视觉效果和玩家反馈，我们计划添加一些特效，如枪口火焰和爆炸效果。

我们设计了一个简单的枪口火焰动画，并将其与射击动作同步播放。这样，当玩家按下射击键时，不仅能看到子弹射出，还能看到枪口冒出的火焰，增强了射击的真实感。

pico-8 cartridge // http://www.pico-8.com
version 41
__lua__
-- t: make basic movement feel nice
--    ❎: fixed cobblestoning
--    ❎: what is a good movement speed
--    t: do banking

-- t: make shooting feel nice!

-- x: normalized diagonals

butarr={1,2,0,3,5,6,3,4,8,7,4,0,1,2,0}

dirx={-1,1, 0,0, -0.7, 0.7,0.7,-0.7}
diry={ 0,0,-1,1, -0.7,-0.7,0.7,0.7}

butarr[0]=0

shiparr={1,3,5,7,9}

shipspr=0

shots={}
shotwait=0

function _init()
 px,py=64,64
 spd=1.4
 lastdir=0
 
 cls(0)
end

function _draw()
 cls(12)
  
  
  
 spr(shiparr[flr(shipspr*2.4+3.5)],px,py,2,2)
 --pset(px,py,8)
 
 for s in all(shots) do
  spr(11,s.x,s.y)
 end
 
 local btnv=btn()&0b1111
 print(btn(),5,5,7)
 print(btnv,5,11,7)
 print(butarr[btnv],5,17,7)
 print(shotwait,5,23,7)
end

function _update60()
 local dir=butarr[btn()&0b1111]
 
 if lastdir!=dir and dir>=5 then
  --anti-cobblestone
  px=flr(px)+0.5
  py=flr(py)+0.5
 end
 
 local dshipspr=0
 
 if dir>0 then
  px+=dirx[dir]*spd
  py+=diry[dir]*spd
  dshipspr=mysgn(dirx[dir])
 end
  
 shipspr+=mysgn(dshipspr-shipspr)*0.15
 shipspr=mid(-1,shipspr,1)
 
 lastdir=dir
 
 if shotwait>0 then
  shotwait-=1
 end
 
 if btn(❎) then
  if shotwait<=0 then
   add(shots,{
    x=px,
    y=py,
    sx=0,
    sy=-1
   })
   shotwait=7
  end
 end
 
 doshots()
end

function doshots()
 for s in all(shots) do
  s.x+=s.sx
  s.y+=s.sy
 end
end

function mysgn(v) 
 return v==0 and 0 or sgn(v)
end
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