feat(mods): expose opt-in final-frame output hooks

docs/mod-api-gen2-compat.md

@@ -546,11 +546,13 @@ gains a field instead of the name gaining a prefix.
   each row's decision in `evolution.check`. The hook passes `data` where Gen 1
   passes `game`; positions 2-4 (mon, row, trigger) match.
 - *The frame (`src/core/Game2.lua`):* hooks `input.step`, `input.pointer`,
-  `render.zones`, `render.compose`, `render.letterbox`, `render.hud`. Each sits
+  `render.zones`, `render.compose`, `render.output_enabled`, `render.output`,
+  `render.letterbox`, `render.hud`. Each sits
   at the same moment `src/core/Game.lua` and `src/render/Renderer.lua` raise it
   -- the logic tick before the pad is read, a pointer the touch overlay gets
   first refusal on, the palette zone list handed to the present pass, the
-  letterbox, and the finished playfield rect -- and carries the same payload.
+  composed frame before GBCFX, the letterbox, and the finished playfield rect
+  -- and carries the same payload.
   `render.hud`'s `gameX` / `gameY` really is where Gold's dialogue boxes and
   menus land, because `Chrome.fitScale` / `fitOrigin` and `World:fitScale`
   compute the same number. `render.zones` is handed `nil` in GBC mode (Gold

docs/modding.md

@@ -440,6 +440,20 @@ oldest queued event as `"action,x,y"` in submitted-frame coordinates, or `nil`.
 This is what lets a mod lay the two passes out as two stacked Game Boy screens,
 or push one onto a second screen, without the engine knowing the layout.
 
+`render.output_enabled` and `render.output` are the later, whole-window seam
+for mods that need the engine's normal composite rather than its separate
+layers. It runs after registered present pipelines and before GBCFX,
+`render.hud`, and touch controls. A mod wraps both hooks: the first returns
+`true` only while output ownership is needed, and the second receives
+`(next, ctx)` with `canvas`, `width`, `height`, `gameX`, `gameY`, `gameWidth`,
+`gameHeight`, `scale`, `dpiX`,
+`dpiY`, and `generation`. Returning `true` from `render.output` takes over the
+window; calling `next(ctx)` keeps the normal presentation. Both hooks default
+to `false`. Enabling the seam requires a full-window canvas for that frame.
+With no `render.output` subscriber, or while `render.output_enabled` is false,
+the existing presentation path is unchanged. `render.compose` takes precedence
+when it owns the frame.
+
 `screen.render_visible` receives `(next, state)` while the main screen is being
 composed. Return `false` to omit that state from drawing, opacity selection and
 palette-zone ownership. The state remains on the stack and keeps its normal

src/core/Game2.lua

@@ -73,7 +73,7 @@ end
 --
 -- Gold composites its own frame (Game2:draw / drawScene) and pumps its own pad
 -- (the FixedStep callback in Game2:load), so none of it goes through
--- src/render/Renderer.lua or src/core/Game.lua.  That explains why the six
+-- src/render/Renderer.lua or src/core/Game.lua.  That explains why the eight
 -- hooks below never used to fire here; it is not a reason they should not.  A
 -- hook is a contract about a MOMENT in the frame, and Gold has every one of
 -- these moments -- so each is raised under the Gen 1 NAME with the Gen 1
@@ -83,6 +83,7 @@ end
 --   input.pointer    uncaptured pointer events       (src/core/Game.lua:887)
 --   render.zones     the palette pass, pre-blit      (src/core/Game.lua:505)
 --   render.compose   the whole-window composite      (Renderer.lua:759)
+--   render.output*   the normal composed frame       (Renderer.lua:1063)
 --   render.letterbox the void around the 160x144 blit (Renderer.lua:840)
 --   render.hud       screen-space UI over the frame  (src/core/Game.lua:521)
 --
@@ -1382,12 +1383,14 @@ function Game2:draw()
   local zoned = type(zones) == "table" and zones[1] ~= nil
 
   -- A present canvas is paid for only when something reads it: the zone pass,
-  -- GBC FX, a mod post-process, or a render.compose subscriber about to be
+  -- GBC FX, a mod post-process, render.compose, or an enabled render.output
-  -- handed the finished frame.  With none of them the frame draws straight to
+  -- subscriber. With none of them the frame draws straight to the screen
-  -- the screen exactly as it always did.
+  -- exactly as it always did.
   local composing = ModRuntime.wantsHook("render.compose")
+  local hasOutputHook = ModRuntime.wantsHook("render.output")
+    and ModRuntime.call("render.output_enabled", function() return false end) == true
   local scene = nil
-  if zoned or fx or composing or Pipelines.wantsPresent() then
+  if zoned or fx or composing or Pipelines.wantsPresent() or hasOutputHook then
     scene = self:presentCanvas(1, w, h)
   end
   if not scene then
@@ -1419,7 +1422,7 @@ function Game2:draw()
   -- untinted one.  On its own the tint rides the final blit and no second
   -- canvas is paid for.
   local source = scene
-  local reread = fx or Pipelines.wantsPresent()
+  local reread = fx or Pipelines.wantsPresent() or hasOutputHook
   if zoned and reread then
     local tinted = self:presentCanvas(2, w, h)
     if tinted then
@@ -1439,9 +1442,18 @@ function Game2:draw()
     -- Post-process pipelines run over the finished composite and before GBC
     -- FX.  Each hands back a canvas; with none registered this returns `source`
     -- unchanged and the frame is byte-identical (Renderer.lua:1058).
-    local scale, _, _, dpi = self:frameFit(w, h)
+    local scale, ox, oy, dpi = self:frameFit(w, h)
     source = Pipelines.present(source, { width = w, height = h, scale = scale,
       dpi = dpi, dpiX = dpi, dpiY = dpi }) or source
+    local outputHandled = hasOutputHook
+      and ModRuntime.call("render.output", function() return false end, {
+        canvas = source, width = w, height = h,
+        gameX = ox, gameY = oy,
+        gameWidth = 160 * scale, gameHeight = 144 * scale,
+        scale = scale, dpiX = dpi, dpiY = dpi,
+        generation = 2,
+      }) == true
+    if not outputHandled then
       if fx then
         GBCFX.present(source, self:pixelScale(w, h))
       else
@@ -1450,6 +1462,7 @@ function Game2:draw()
         G.setShader()
       end
     end
+  end
   G.pop()
   G.setColor(1, 1, 1, 1)
   self:drawHud(w, h)

src/render/Renderer.lua

@@ -768,11 +768,12 @@ function Renderer:endFrame(zones, worldZones)
     end
   end
 
-  -- A post-process pipeline needs the whole composite in a canvas for the
+  -- Post-process pipelines, GBC FX and an enabled final-output owner need the
-  -- same reason GBC FX does, so either one alone is enough to take the
+  -- whole composite in a canvas. With none of them, the frame draws straight
-  -- present path; with neither, the frame draws straight to the screen
+  -- to the screen exactly as it always did.
-  -- exactly as it always did.
+  local hasOutputHook = Runtime.wantsHook("render.output")
-  local needPresent = GBCFX.active() or Pipelines.wantsPresent()
+    and Runtime.call("render.output_enabled", function() return false end) == true
+  local needPresent = GBCFX.active() or Pipelines.wantsPresent() or hasOutputHook
   local present = nil
   if needPresent then
     if not self.presentCanvas or self.presentCanvas:getWidth() ~= ww
@@ -1057,6 +1058,16 @@ function Renderer:endFrame(zones, worldZones)
     -- this returns `present` unchanged and the frame is byte-identical.
     local composed = Pipelines.present(present,
       { width = ww, height = wh, scale = Sp, dpi = dpiY, dpiX = dpiX, dpiY = dpiY }) or present
+    local outputHandled = hasOutputHook
+      and Runtime.call("render.output", function() return false end, {
+        canvas = composed,
+        width = ww, height = wh,
+        gameX = ox, gameY = oy,
+        gameWidth = vpw, gameHeight = vph,
+        scale = Sp, dpiX = dpiX, dpiY = dpiY,
+        generation = 1,
+      }) == true
+    if not outputHandled then
       if GBCFX.active() then
         -- shader grid/shadow math is in framebuffer pixels
         GBCFX.present(composed, Sp)
@@ -1067,6 +1078,7 @@ function Renderer:endFrame(zones, worldZones)
         love.graphics.draw(composed, 0, 0)
       end
     end
+  end
   self.worldActive = false
   self.uprightActive = false
   self.worldOverride = nil

tests/engine/gate_gen2_mod_api.lua

@@ -434,7 +434,8 @@ local GEN2_HOOKS = {
   -- pointer with the touch overlay given first refusal, the palette zone list
   -- handed to the present pass, the letterbox and the HUD rect.
   "input.step", "input.pointer",
-  "render.zones", "render.compose", "render.letterbox", "render.hud",
+  "render.zones", "render.compose", "render.output_enabled", "render.output",
+  "render.letterbox", "render.hud",
 }
 
 local function assertShared(name, sites, kind)

tests/engine/gen2_render_output_seam.lua

@@ -0,0 +1,47 @@
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+local T = require("tests.modkit")
+local Game2 = require("src.core.Game2")
+local Runtime = require("src.mods.Runtime")
+local Hooks = require("src.mods.Hooks")
+
+local savedHooks = Runtime.hooks
+local hooks = Hooks.new()
+Runtime.hooks = hooks
+
+local received
+hooks:wrap("render.output", function(_, context)
+  received = context
+  return true
+end, 0, "test")
+hooks:wrap("render.output_enabled", function() return false end, 0, "test")
+
+local canvas = love.graphics.newCanvas(640, 480)
+local presentCalls = 0
+local game = setmetatable({
+  frameFit = function() return 3, 80, 24, 1, 480, 432 end,
+  presentCanvas = function() presentCalls = presentCalls + 1 return canvas end,
+  drawScene = function() end,
+  drawHud = function() end,
+}, Game2)
+
+Game2.draw(game)
+T.eq(received, nil, "a disabled Gold output hook does not run")
+T.eq(presentCalls, 0, "a disabled Gold output hook keeps the direct path")
+
+hooks:wrap("render.output_enabled", function() return true end, 10, "test")
+Game2.draw(game)
+T.check(received ~= nil, "Gold raises render.output for an enabled subscriber")
+T.eq(received and received.canvas, canvas,
+  "Gold hands render.output the finished present canvas")
+T.eq(received and received.generation, 2,
+  "Gold identifies the output context without changing Gen 1")
+T.eq(received and received.gameX, 80, "Gold output carries the fitted game X")
+T.eq(received and received.gameY, 24, "Gold output carries the fitted game Y")
+T.eq(received and received.gameWidth, 480,
+  "Gold output carries the fitted game width")
+T.eq(received and received.gameHeight, 432,
+  "Gold output carries the fitted game height")
+
+Runtime.hooks = savedHooks
+T.finish("gen2 render output seam")

tests/mod_graphics_tests.lua

@@ -987,6 +987,33 @@ check(fallback.style == "doublecircle",
       "a hook naming an unregistered style falls back to the vanilla bits")
 Runtime.install(Events.new(), Hooks.new(), {})
 
+-- ------- gated final-output ownership
+
+local outputHooks = Hooks.new()
+Runtime.install(Events.new(), outputHooks, {})
+local outputCalls, outputContext = 0, nil
+outputHooks:wrap("render.output", function(nextLink, context)
+  outputCalls, outputContext = outputCalls + 1, context
+  return true
+end, 0, "test")
+outputHooks:wrap("render.output_enabled", function() return false end, 0, "test")
+Renderer:init()
+Renderer.presentCanvas = nil
+Renderer:beginFrame(false)
+Renderer:endFrame(nil, nil)
+check(outputCalls == 0 and Renderer.presentCanvas == nil,
+      "a disabled output hook leaves the direct render path untouched")
+
+outputHooks:wrap("render.output_enabled", function() return true end, 10, "test")
+Renderer:init()
+Renderer.presentCanvas = nil
+Renderer:beginFrame(false)
+Renderer:endFrame(nil, nil)
+check(outputCalls == 1 and outputContext and outputContext.canvas,
+      "an enabled output hook receives the finished frame")
+check(outputContext and outputContext.generation == 1,
+      "the output context identifies the active generation")
+
 -- ------- asset transforms
 
 local function seedTransform(id, source)