pokecenter machines, water occlusion

lib/VoxelScene.lua

@@ -583,8 +583,40 @@ end
 -- The overworld's alone: the staged battle draws its water plain, always --
 -- its placed camera reads this pass wrong, and a stage set wants painted
 -- water anyway (see BattleScene, where the choice is argued).
+-- ------- and why the flat draw happens FIRST, every time
+--
+-- The reflective pass writes no depth -- it cannot, the depth canvas is
+-- detached for the length of it so the shader can READ it -- and it does its
+-- own depth test against that texture instead. That test asks whether
+-- something opaque is in front, and it answers correctly for every case but
+-- one: WATER IN FRONT OF WATER. Nothing puts water in the depth buffer, so
+-- no lake can hide another, and the pass simply paints them in mesh order.
+--
+-- On flat water that never mattered, because every surface lies in the one
+-- plane at its own recessed height and a farther sheet always lands farther
+-- down the screen. THE WORLD CURVE ENDS THAT. The bend drops the world by
+-- the square of its distance, so the far side of the map swings down and
+-- back up into the near field of view -- and a sheet of sea a hundred and
+-- fifty tiles away, drawn later in the same mesh, paints straight over the
+-- pond at the player's feet. That is the tall grass and the water "from the
+-- other side of the map": not a reflection of them, THEM, rasterised on top
+-- of the water in front of you.
+--
+-- So the meshes go down flat first, through the ordinary scene shader with
+-- depth writes on, and the reflective pass draws over the top of what
+-- survived. Three things fall out of it and all three are wanted: the depth
+-- buffer now holds the water surface, so the pass's own test throws the far
+-- sheet away; the reflection COPY holds it too, so a ray grazing another
+-- part of the lake reads water rather than the void behind it; and the flat
+-- draw is the same fallback this function already ended with, so a frame
+-- that cannot run the reflective pass is unchanged.
+--
+-- It costs one more rasterisation of the water meshes. Water is a small
+-- share of a frame's triangles and this is the cheapest shader in the mode.
 function VoxelScene.drawWater(draws, cast)
-  local plain = true
+  for _, d in ipairs(draws) do
+    Voxel3D.draw(d[1], d[2], d[3])
+  end
   if Water.enabled() and Voxel3D.depthReadable() then
     local mirror, depth = Voxel3D.beginWater(cast)
     local w, h = Voxel3D.size()
@@ -602,20 +634,15 @@ function VoxelScene.drawWater(draws, cast)
         Water.draw(d[1], d[2], d[3])
       end
       Water.finish()
-      plain = false
     end
     -- Unconditionally, and OUTSIDE the success branch: beginWater unbinds
     -- the shader and the depth mode BEFORE it can discover it cannot go on,
     -- so a frame that bails halfway through has to be put back together
-    -- exactly like one that succeeded -- otherwise the plain draw below (and
-    -- every pass after it) runs with no shader and no depth test.
+    -- exactly like one that succeeded -- otherwise every pass after it runs
+    -- with no shader and no depth test. (What a bail leaves on screen is the
+    -- flat draw above, which is where this function used to end anyway.)
     Voxel3D.endWater()
   end
-  if plain then
-    for _, d in ipairs(draws) do
-      Voxel3D.draw(d[1], d[2], d[3])
-    end
-  end
 end
 
 -- A stamp of everything the sun pass depends on. Nothing in it moving