replace grab_butts with act

marshaling through a table is a waste of time, the duplication betweeen
positive and negative thrust vectors is pointless, and pre-multiplying
thrust complicates "stay in a box" goals later on.

updatedshmup.p8

@@ -397,23 +397,6 @@ function dropshadow(str, x, y, col)
  print(str, x, y, col)
 end
 
-function grab_p1_butts()
- if state ~= game then
-  local r = {0,0,0,0,0}
-  r[0] = 0
-  return r
- end
- local b = btn()
- return {
-  [0]=b&0x1,
-  [1]=(b&0x2)>>1,
-  [2]=(b&0x4)>>2,
-  [3]=(b&0x8)>>3,
-  [4]=(b&0x10)>>4,
-  [5]=(b&0x20)>>5
- }
-end
-
 -->8
 --ship behavior
 
@@ -448,12 +431,12 @@ end
 function ship_m:move()
  self:refresh_shield()
  self.power = min(self.max_power, self.power + self.generator)
- butt = self:grab_butts()
- if (butt[5] > 0) self:maybe_shoot(self.main_gun)
- if (butt[4] > 0) self:maybe_shoot(self.special_gun)
- if (butt[0]-butt[1] ~= 0 or butt[2]-butt[3] ~= 0) spark(self.sparks, self.x + 4*self.size, self.y + 4*self.size, butt, self.thrust, self.sparkodds)
- self.xmomentum += (self.thrust * butt[1]) - (self.thrust * butt[0])
- self.ymomentum += (self.thrust * butt[3]) - (self.thrust * butt[2])
+ local dx, dy, shoot_spec, shoot_main = self:act()
+ if (shoot_main) self:maybe_shoot(self.main_gun)
+ if (shoot_spec) self:maybe_shoot(self.special_gun)
+ if (dx ~= 0 or dy ~= 0) spark(self.sparks, self.x + 4*self.size, self.y + 4*self.size, dx*2.5, dy*2.5, self.sparkodds)
+ self.xmomentum += dx
+ self.ymomentum += dy
  self.xmomentum = mid(-self.maxspd, self.maxspd, self.xmomentum)
  self.ymomentum = mid(-self.maxspd, self.maxspd, self.ymomentum)
  
@@ -869,16 +852,18 @@ player = ship_m.new{
  thrust = 0.25, -- momentum added from button
  drag = 0.125, -- momentum lost per frame
  slip = false, -- does not slide down screen
- grab_butts = function(self)  -- fetch buttons
-  local butts = grab_p1_butts()
-  if butts[0] == butts[1] then
-   self.sprite = 1
-  elseif butts[0] > 0 then
+ act = function(self)  -- fetch buttons
+  local b,th = btn(),self.thrust
+  local blr = b&0x3
+  if blr == 1 then
    self.sprite=17
-  else
+  elseif blr==2 then
    self.sprite=18
+  else
+   self.sprite=1
   end
-  return butts
+  --dx, dy, shoot_spec, shoot_main
+  return (((b&0x2)>>1) - (b&0x1)) * th, (((b&0x8)>>3) - ((b&0x4)>>2)) * th, (b&0x10) > 0, (b&0x20) > 0
  end
 }
 mknew(player,
@@ -912,18 +897,12 @@ frownie = ship_m.new{
  thrust = 0.12, -- momentum added from button
  drag = 0.07, -- momentum lost per frame
  slip = true,
- grab_butts = function(discard_self)
-  -- buttons are effectively analog
-  -- and negative buttons work just fine!
-  local butts = {}
-  local tstate = (1 + flr(4*t() + 0.5)) % 6
-  butts[0] = ((tstate==1 or tstate==2) and 1) or 0
-  butts[1] = ((tstate==4 or tstate==5) and 1) or 0
-  for b=2, 5 do
-   butts[b]=0
-  end
-  return butts
- end, -- button fetch algorithm
+ act = function(self)
+  local tstate,dx = (1 + flr(4*t() + 0.5)) % 6,0
+  if (tstate==1 or tstate==2) dx=-self.thrust
+  if (tstate>=4) dx=self.thrust
+  return dx,0,false,false
+ end,
 }
 mknew(frownie)
 
@@ -962,10 +941,9 @@ spewy = frownie.new{
  generator=0.5,
  fire_off_x=4,
  fire_off_y = 7,
- grab_butts=function()
-  local butts=frownie.grab_butts()
-  butts[5]=1
-  return butts
+ act=function()
+  local dx,dy,shoot_spec=frownie.act(self)
+  return dx, dy, shoot_spec, true
  end
 }
 mknew(spewy, function(ship)
@@ -1000,12 +978,11 @@ mknew(chasey, function(ship)
  ship.main_gun=ship.main_gun or zap_gun.new{enemy=true}
 end)
 
-function chasey:grab_butts()
- local butts = {[0]=0,0,0,0,0,0}
- if (self.x < primary_ship.x) butts[1] = 1
- if (self.x > primary_ship.x) butts[0] = 1
- if (self.x - 16 < primary_ship.x and self.x + 16 > primary_ship.x) butts[5] = 1
- return butts
+function chasey:act()
+ local dx = 0
+ if (self.x < primary_ship.x) dx=self.thrust
+ if (self.x > primary_ship.x) dx=-self.thrust
+ return dx, 0, false, self.x - 16 < primary_ship.x and self.x + 16 > primary_ship.x
 end
 
 xl_chasey=chasey.new{
@@ -1021,10 +998,10 @@ xl_chasey=chasey.new{
  shield = 5,
  boss = true,
  slip = false,
- grab_butts = function(self)
-  local butts = chasey.grab_butts(self)
-  if (self.y < 4) butts[3] = 1
-  return butts
+ act = function(self)
+  local dx,dy,shoot_spec,shoot_main = chasey.act(self)
+  if (self.y < 4) dy=self.thrust
+  return dx,dy,shoot_spec,shoot_main
  end,
  draw = function(self)
   if(self.fx_pal) pal(self.fx_pal)
@@ -1510,18 +1487,12 @@ like a player pushing buttons.
 the player ship actually reads
 buttons for this.
 
-grab_butts - ship thrust control
-based on btn() api. returns a
-table indexed from 0..5 with
-0 to not push this button and 1
-to push it. ships can use
-fractional or out-of-range
-numbers to get varying amounts
-of thrust, including using
-negative numbers for thrust in
-the opposite direction. 4 and 5
-just check for nonzeroness to
-attempt to fire.
+act -- returns new acceleration:
+dx, dy, shoot_spec, shoot_main.
+dx and dy are change in momentum
+in px/frame. this is controls
+only -- friction is handled in
+ship:move (`drag` value).
 
 ships hitting another ship take
 1 damage per frame of overlap.
@@ -1800,9 +1771,7 @@ function boom(x,y,boominess,is_boss)
  local boombonus = min(0.05 * boominess, 1.25)
  for _=1,boominess do
   local angle = rnd(1)
-  local butts = {0, sin(angle), 0}
-  butts[0] = cos(angle)
-  spark(sp,x+4,y+4,butts,boombase+rnd(boombonus),1, true)
+  spark(sp,x+4,y+4,cos(angle), sin(angle),boombase+rnd(boombonus),1, true)
  end
  return
 end
@@ -1822,17 +1791,16 @@ function spark_particle:draw()
  pset(self.x,self.y,self.sprs[self.sidx])
 end
 
-function spark(sprs, x, y, butts, thrust, odds, fg)
+function spark(sprs, x, y, dx, dy, odds, fg)
  if (sprs==nil or flr(rnd(odds)) ~= 0) return
- thrust *= 2.5
  local target = fg and intangibles_fg or intangibles_bg
  target:push_back(spark_particle.new{
   x = x + rnd(4) - 2,
   y = y + rnd(4) - 2,
   sprs = sprs,
   sidx = 1,
-  dx = (butts[0] - butts[1]) * thrust + rnd(2) - 1,
-  dy = (butts[2] - butts[3]) * thrust + rnd(2) - 1,
+  dx = dx + rnd(2) - 1,
+  dy = dy + rnd(2) - 1,
  })
 end
 -->8