# ============================================================================
# water.ludic — still water for the valley floor: a level plane over a region,
# drawn after the opaque scene, showing only where the ground lies below it.
# Sky reflection with fresnel, sun glitter, scrolling ripple normals, a depth
# tinted body read from the scene depth, and soft shores.
# ============================================================================

var water_mesh: Mesh = null
var water_prog: int = 0
var water_level: int = 0
var water_cx: int = 0
var water_cz: int = 0
var water_ex: int = 0
var water_ez: int = 0
var water_on: bool = false
# Where a body is standing in the water and how hard it is disturbing it. The game sets it;
# strength 0 means nobody is in the water and the whole term is skipped.
var wt_wade_x: int = 0
var wt_wade_z: int = 0
var wt_wade_s: int = 0
var water_refl: Target = null            # the world mirrored in the surface, half resolution
var water_refl_div: int = 2              # R3D_REFLDIV overrides: 2 = half res, 4 = quarter
var water_saved: words = null            # the real camera's matrices, restored after the pass
var water_dumped: bool = false
# Several still-water planes, each at its own level over its own bounds: the sea round an
# island and a lake a hundred metres above it cannot be one surface. Each draws the same way;
# only one - the first added with `reflect` - gets the planar reflection pass, because every
# mirrored plane is another full scene pass. water_level / water_cx ... mirror that one, so
# code written against a single plane still reads the surface that reflects.
const WATER_MAX: int = 8
var wb_n: int = 0
var wb_level: words = null
var wb_cx: words = null
var wb_cz: words = null
var wb_ex: words = null
var wb_ez: words = null
var wb_reflect: words = null
var wb_primary: int = -1               # the body the reflection pass mirrors, or -1

# Render the scene through a camera mirrored in the water plane into water_refl,
# clipping everything below the surface; terrain, scattered layers and sky.
function water_reflection_pass() -> void {
  if wb_primary < 0 { return }            # no body reflects: nothing to mirror
  if water_refl == null {
    if r3d_env_has("R3D_REFLDIV") { water_refl_div = Text.to_int(r3d_env("R3D_REFLDIV")) }
    if water_refl != null { target_free(water_refl) }
    # sized from the scene target, not the window: with a render scale below 1 the frame
    # this reflection is composited into is smaller than the drawable, and a reflection
    # rendered at the window's size would be paying for pixels the water never samples
    water_refl = target_new(post_w / water_refl_div, post_h / water_refl_div, GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT, true, GL_LINEAR)
    water_saved = words(16 * 4 + 3)
  }
  # save the camera
  m4_copy(water_saved, cam_view)
  m4_copy(mem_off(water_saved, 64), cam_vp)
  m4_copy(mem_off(water_saved, 128), cam_inv_vp)
  let sx = cam_pos[0];  let sy = cam_pos[1];  let sz = cam_pos[2]
  # the mirrored camera: view' = view * R, R reflecting y about the surface (y' = 2L - y).
  # R has determinant -1, so the winding flips (front faces culled below) and the image
  # lands exactly where the main camera's pixels expect the reflection.
  let eye = v3_new(sx, f_sub(f_mul(F_TWO, water_level), sy), sz)
  let refl = m4_new()
  refl[5] = f_neg1()
  refl[13] = f_mul(F_TWO, water_level)
  let mv = words(16)
  m4_mul(mv, water_saved, refl)
  m4_copy(cam_view, mv)
  free(mv);  free(refl)
  let fwd = words(3);  let up = words(3);  let at = words(3)
  m4_mul(cam_vp, cam_proj, cam_view)
  m4_inverse(cam_inv_vp, cam_vp)
  v3_copy(cam_pos, eye)
  r3d_clip_y = f_sub(water_level, fl(0.05))
  target_bind(water_refl)
  gpu_depth_test(true)
  gpu_depth_func(GL_LESS)
  gpu_depth_write(true)
  gpu_cull(true)
  gpu_cull_face(GL_FRONT)                  # the mirror flips the winding
  gpu_clear_color(0.0, 0.0, 0.0, 1.0)
  gpu_clear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
  sc_freeze = true
  let sb = sc_skip_blade
  sc_skip_blade = true                    # blades are invisible at this scale in a reflection
  ter_reflect = true
  prof_cpu_mark("reflection setup")
  terrain_draw()
  prof_cpu_mark("reflection terrain")
  scene_draw()
  prof_cpu_mark("reflection scene")
  r3d_draw_sky()
  prof_cpu_mark("reflection sky")
  ter_reflect = false
  sc_skip_blade = sb
  sc_freeze = false
  gpu_cull_face(GL_BACK)
  if r3d_env_has("R3D_DUMP_REFL") and not water_dumped { water_dumped = true;  tex_dump(water_refl.color, water_refl.w, water_refl.h, "build/dbg_refl.ppm") }
  # restore
  r3d_clip_y = 0xCF000000
  m4_copy(cam_view, water_saved)
  m4_copy(cam_vp, mem_off(water_saved, 64))
  m4_copy(cam_inv_vp, mem_off(water_saved, 128))
  v3_set(cam_pos, sx, sy, sz)
  free(eye);  free(fwd);  free(up);  free(at)
  gpu_fb_bind(0)
}

# Is any of the mirrored water in view? The reflection pass is a second copy of the terrain, the
# vegetation and the actors - 170-260 draws - and it ran on every frame of a map with a lake, looking
# straight down at a meadow included, where no pixel samples it. The mirrored body's bounds are cut
# into rectangles (water_cells_build) that count where the ground lies below the water, and the pass
# runs when one of those rectangles meets the view frustum and its water is not all dry where it shows,
# outside the frame or behind the ground (wb_cell_occluded). Past 16 rectangles in view it runs without
# asking, so it errs on the side of running. R3D_REFL_ALWAYS=1 runs it on every frame, for comparing.
# Mac, the five shot viewpoints: looking down at the meadow (c) 225 reflection draws -> none; every view
# with the lake in it unchanged, byte-identical frames.
var wb_cells: words = null             # x0, z0, x1, z1 of each rectangle with water showing
var wb_ncells: int = -1                # -1: not built for the current mirrored body
var wb_blocks: words = null            # x0, z0, x1, z1, first cell, cells past the last - of each block
var wb_nblocks: int = 0
var wb_refl_always: int = -1
var wb_dbg: int = -1
var wb_build_us: long = 0              # how long the last water_cells_build took (R3D_REFL_DBG prints it)
function water_reflect_visible() -> bool {
  if wb_primary < 0 { return false }
  if wb_refl_always < 0 { wb_refl_always = 0;  if r3d_env_has("R3D_REFL_ALWAYS") { wb_refl_always = 1 } }
  if wb_refl_always == 1 or ter_heights == null { return true }
  if wb_ncells < 0 { let t0 = gl_now_us();  water_cells_build();  wb_build_us = gl_now_us() - t0 }
  if wb_dbg < 0 { wb_dbg = 0;  if r3d_env_has("R3D_REFL_DBG") { wb_dbg = 1 } }
  if wb_dbg == 1 {
    # R3D_REFL_DBG: once, what the test is made of and how much of it is in view
    wb_dbg = 2
    var seen = 0
    var hidden = 0
    for i in 0 .. wb_ncells { if wb_cell_visible(i) { seen += 1;  if wb_cell_occluded(i) { hidden += 1 } } }
    print(`water reflection test: {wb_ncells} wet rectangles in {wb_nblocks} blocks (built in {wb_build_us} us), {seen} in view, {hidden} of them behind the ground`)
  }
  # A rectangle in the frustum can still be behind the ground or dry where it shows: standing on a shore
  # above the lake and looking down at your feet puts water inside the view and none of it on screen.
  # The first 16 in view are checked against the height field; past that the pass simply runs.
  var checked = 0
  for b in 0 .. wb_nblocks {
    let o = b * 6
    if not wb_rect_visible(wb_blocks[o], wb_blocks[o + 1], wb_blocks[o + 2], wb_blocks[o + 3]) { continue }
    for i in wb_blocks[o + 4] .. wb_blocks[o + 5] {
      if not wb_cell_visible(i) { continue }
      if checked >= 16 { return true }
      checked += 1
      if not wb_cell_occluded(i) { return true }
    }
  }
  return false
}
# A flat rectangle at the water's level against the view's side planes: hidden when all four corners
# lie outside one plane. (A bounding sphere was the first version: a 156 m cell's sphere reached into
# the view from a lake the camera had its back to, and the pass never skipped.)
function wb_rect_visible(x0: int, z0: int, x1: int, z1: int) -> bool {
  if cam_planes == null { return true }
  for p in 0 .. 4 {
    let q = p * 4
    let a = cam_planes[q];  let c = cam_planes[q + 2]
    let by = f_add(f_mul(cam_planes[q + 1], water_level), cam_planes[q + 3])
    let ax0 = f_mul(a, x0);  let ax1 = f_mul(a, x1);  let cz0 = f_mul(c, z0);  let cz1 = f_mul(c, z1)
    if f_ls(f_add(f_add(ax0, cz0), by), F_ZERO) and f_ls(f_add(f_add(ax1, cz0), by), F_ZERO) and f_ls(f_add(f_add(ax0, cz1), by), F_ZERO) and f_ls(f_add(f_add(ax1, cz1), by), F_ZERO) { return false }
  }
  return true
}
function wb_cell_visible(i: int) -> bool {
  let o = i * 4
  return wb_rect_visible(wb_cells[o], wb_cells[o + 1], wb_cells[o + 2], wb_cells[o + 3])
}
# Is the water at (x, z) out of sight - dry ground there, outside the frame, or behind the ground? The
# sight line is sampled at seven points short of both ends, with half a metre (and a little more with
# distance) of margin, so a far ridge the drawn terrain rounds off never hides real water. A camera at
# or under the surface hides nothing behind the ground.
function wb_point_hidden(x: int, z: int) -> bool {
  if f_gt(terrain_height(x, z), f_add(water_level, fl(0.05))) { return true }
  if not cam_sphere_visible(x, water_level, z, F_HALF) { return true }
  let ey = cam_pos[1]
  if not f_gt(ey, water_level) { return false }
  let dx = f_sub(x, cam_pos[0]);  let dz = f_sub(z, cam_pos[2])
  let margin = f_add(F_HALF, f_mul(f_sqrt(f_add(f_mul(dx, dx), f_mul(dz, dz))), fl(0.004)))
  for k in 1 .. 8 {
    let t = fr(k, 8)
    let sy = f_add(ey, f_mul(f_sub(water_level, ey), t))
    if f_gt(terrain_height(f_add(cam_pos[0], f_mul(dx, t)), f_add(cam_pos[2], f_mul(dz, t))), f_add(sy, margin)) { return true }
  }
  return false
}
# every point the wet test sampled (the centre and four near the corners) is out of sight
function wb_cell_occluded(i: int) -> bool {
  let o = i * 4
  let x0 = wb_cells[o];  let z0 = wb_cells[o + 1];  let x1 = wb_cells[o + 2];  let z1 = wb_cells[o + 3]
  let cx = f_mul(f_add(x0, x1), F_HALF);  let cz = f_mul(f_add(z0, z1), F_HALF)
  let ox = f_mul(f_sub(x1, x0), fl(0.45));  let oz = f_mul(f_sub(z1, z0), fl(0.45))
  if not wb_point_hidden(cx, cz) { return false }
  if not wb_point_hidden(f_sub(cx, ox), f_sub(cz, oz)) { return false }
  if not wb_point_hidden(f_add(cx, ox), f_sub(cz, oz)) { return false }
  if not wb_point_hidden(f_sub(cx, ox), f_add(cz, oz)) { return false }
  return wb_point_hidden(f_add(cx, ox), f_add(cz, oz))
}
function wb_cell_add(x0: int, z0: int, x1: int, z1: int) -> void {
  let o = wb_ncells * 4
  wb_cells[o] = x0;  wb_cells[o + 1] = z0;  wb_cells[o + 2] = x1;  wb_cells[o + 3] = z1
  wb_ncells += 1
}
function wb_block_add(x0: int, z0: int, x1: int, z1: int, first: int) -> void {
  if wb_ncells <= first { return }
  let o = wb_nblocks * 6
  wb_blocks[o] = x0;  wb_blocks[o + 1] = z0;  wb_blocks[o + 2] = x1;  wb_blocks[o + 3] = z1
  wb_blocks[o + 4] = first;  wb_blocks[o + 5] = wb_ncells
  wb_nblocks += 1
}
function wb_wet(x: int, z: int, off: int) -> bool {
  if f_ls(terrain_height(x, z), water_level) { return true }
  if off == 0 { return false }
  if f_ls(terrain_height(f_sub(x, off), f_sub(z, off)), water_level) { return true }
  if f_ls(terrain_height(f_add(x, off), f_sub(z, off)), water_level) { return true }
  if f_ls(terrain_height(f_sub(x, off), f_add(z, off)), water_level) { return true }
  return f_ls(terrain_height(f_add(x, off), f_add(z, off)), water_level)
}
# Over the height map, 32 m rectangles (at most 512 a side) tested at five points and kept in blocks of
# 8 x 8, so a block out of view skips its rectangles in one test - looking away from the water was a
# walk of every rectangle, every frame. The body beyond the map (a sea runs far past it) is 64 x 64
# coarse rectangles tested at their centre, in one last block, which only ever matter kilometres away.
const WB_BLOCK: int = 8
function water_cells_build() -> void {
  let bx0 = f_sub(water_cx, water_ex);  let bx1 = f_add(water_cx, water_ex)
  let bz0 = f_sub(water_cz, water_ez);  let bz1 = f_add(water_cz, water_ez)
  let th = fi(TERRAIN_HALF)
  let tx0 = f_max(bx0, f_sub(ter_ox, th));  let tx1 = f_min(bx1, f_add(ter_ox, th))
  let tz0 = f_max(bz0, f_sub(ter_oz, th));  let tz1 = f_min(bz1, f_add(ter_oz, th))
  let inside = f_gt(tx1, tx0) and f_gt(tz1, tz0)
  var cell = fi(32)
  var nx = 0
  var nz = 0
  if inside {
    let span = f_max(f_sub(tx1, tx0), f_sub(tz1, tz0))
    if f_gt(f_div(span, cell), fi(512)) { cell = f_div(span, fi(512)) }
    nx = f_to_int(f_div(f_sub(tx1, tx0), cell)) + 1
    nz = f_to_int(f_div(f_sub(tz1, tz0), cell)) + 1
  }
  if wb_cells != null { free(wb_cells) }
  if wb_blocks != null { free(wb_blocks) }
  wb_cells = words((nx * nz + 64 * 64) * 4)
  let nbx = (nx + WB_BLOCK - 1) / WB_BLOCK
  let nbz = (nz + WB_BLOCK - 1) / WB_BLOCK
  wb_blocks = words((nbx * nbz + 1) * 6)
  wb_ncells = 0
  wb_nblocks = 0
  let off = f_mul(cell, fl(0.45))
  let half = f_mul(cell, F_HALF)
  for bz in 0 .. nbz {
    for bx in 0 .. nbx {
      let first = wb_ncells
      var iz = bz * WB_BLOCK
      while iz < (bz + 1) * WB_BLOCK and iz < nz {
        let z0 = f_add(tz0, f_mul(fi(iz), cell))
        var ix = bx * WB_BLOCK
        while ix < (bx + 1) * WB_BLOCK and ix < nx {
          let x0 = f_add(tx0, f_mul(fi(ix), cell))
          if wb_wet(f_add(x0, half), f_add(z0, half), off) { wb_cell_add(x0, z0, f_add(x0, cell), f_add(z0, cell)) }
          ix += 1
        }
        iz += 1
      }
      let x0 = f_add(tx0, f_mul(fi(bx * WB_BLOCK), cell));  let z0 = f_add(tz0, f_mul(fi(bz * WB_BLOCK), cell))
      wb_block_add(x0, z0, f_add(x0, f_mul(fi(WB_BLOCK), cell)), f_add(z0, f_mul(fi(WB_BLOCK), cell)), first)
    }
  }
  let first = wb_ncells
  let cw = f_div(f_sub(bx1, bx0), fi(64))
  let ch = f_div(f_sub(bz1, bz0), fi(64))
  for iz in 0 .. 64 {
    let z0 = f_add(bz0, f_mul(fi(iz), ch));  let z1 = f_add(z0, ch)
    for ix in 0 .. 64 {
      let x0 = f_add(bx0, f_mul(fi(ix), cw));  let x1 = f_add(x0, cw)
      # inside the height map's rectangle: the fine cells above cover it
      if inside and not f_ls(x0, tx0) and not f_gt(x1, tx1) and not f_ls(z0, tz0) and not f_gt(z1, tz1) { continue }
      if wb_wet(f_add(x0, f_mul(cw, F_HALF)), f_add(z0, f_mul(ch, F_HALF)), 0) { wb_cell_add(x0, z0, x1, z1) }
    }
  }
  wb_block_add(bx0, bz0, bx1, bz1, first)
}

# the program and the plane are the process's, built once; the bodies are the map's
function water_setup() -> void {
  if water_prog != 0 { return }
  water_mesh = mesh_grid(2, F_HALF)
  water_prog = r3d_program("water.vert", "water.frag", "")
  wb_level = words(WATER_MAX);  wb_cx = words(WATER_MAX);  wb_cz = words(WATER_MAX)
  wb_ex = words(WATER_MAX);  wb_ez = words(WATER_MAX);  wb_reflect = words(WATER_MAX)
}
function water_bodies_clear() -> void {
  wb_n = 0
  wb_primary = -1
  wb_ncells = -1
  water_on = false
}
# Add a plane at `level` over (cx, cz) +- (ex, ez); true `reflect` makes it the mirrored one
# if none is yet. Returns its index, or -1 once WATER_MAX are in use.
function water_body_add(level: int, cx: int, cz: int, ex: int, ez: int, reflect: bool) -> int {
  water_setup()
  if wb_n >= WATER_MAX { return -1 }
  let i = wb_n
  wb_level[i] = level;  wb_cx[i] = cx;  wb_cz[i] = cz;  wb_ex[i] = ex;  wb_ez[i] = ez
  wb_reflect[i] = 0
  if reflect { wb_reflect[i] = 1 }
  wb_n += 1
  water_on = true
  if reflect and wb_primary < 0 {
    wb_primary = i
    wb_ncells = -1
    water_level = level;  water_cx = cx;  water_cz = cz;  water_ex = ex;  water_ez = ez
  }
  return i
}
# one reflecting plane: what this function always meant, without a new mesh and program
# every time it is called
function water_init(level: int, cx: int, cz: int, ex: int, ez: int) -> void {
  water_bodies_clear()
  water_body_add(level, cx, cz, ex, ez, true)
}

# call after the opaque pass, before the sky: blends over the resolved depth
function water_draw(depth_tex: int) -> void {
  if not water_on or wb_n == 0 { return }
  let p = water_prog
  gpu_use_program(p)
  u_mat4(gpu_uniform(p, "u_view"), cam_view)
  u_mat4(gpu_uniform(p, "u_proj"), cam_proj)
  u_mat4(gpu_uniform(p, "u_inv_vp"), cam_inv_vp)
  # gl_FragCoord here runs over the scene target, which is post_w x post_h — not the
  # window. They are the same size only at a render scale of 1; at anything less, taking
  # the window's size sent the refraction and depth reads into the wrong corner of the
  # frame, and the lake showed a squashed copy of it instead of its own bed.
  u_f2(gpu_uniform(p, "u_screen"), fi(post_w), fi(post_h))
  # Read into locals first. Passing these three globals straight into the call gives the
  # shader wrong values - the whole lake churns instead of a patch of it - and a single dead
  # `let junk = wt_wade_x` above the same unchanged call is enough to make it correct again.
  # It is a codegen fault, not a fact about this shader: the values print identically either
  # way at the line above, and it is not the position in the function (it does the same bound
  # right after gpu_use_program) nor the nested gpu_uniform call (hoisting that changes
  # nothing). Verified by picture, both backends. Read a global into a local before handing it
  # to a uniform call.
  let wx = wt_wade_x
  let wz = wt_wade_z
  let ws = wt_wade_s
  u_f3(gpu_uniform(p, "u_wade"), wx, wz, ws)
  var ron = F_ZERO
  if water_refl != null and wb_primary >= 0 {
    # bind on its own unit first: generating the mip chain re-binds the texture on the active unit,
    # and it must not displace the depth texture the shader reads for the shore
    r3d_bind_2d(p, "u_refl", 1, water_refl.color);  ron = F_ONE
    gpu_tex_param(GPU_TEX2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR)
    gpu_tex_mips(GPU_TEX2D)
  }
  r3d_bind_2d(p, "u_depth", 0, depth_tex)
  r3d_bind_2d(p, "u_scene", 2, post_scene.color)
  sky_bind_lighting(p)
  shadow_bind(p)
  fog_bind(p)
  # Opaque. The surface composites the refracted bed itself, so there is nothing for
  # hardware blending to do — and an alpha was what left see-through gaps in the foam
  # and a clear band at the shore wide enough to give the plane away.
  gpu_blend(false)
  gpu_blend_func(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
  # the surface writes depth: the ambient-occlusion and temporal passes read the frame's depth,
  # and the bed 9 m below the shore would otherwise darken a band along the water line
  gpu_depth_write(true)
  gpu_cull(false)
  # every body is the same plane at its own level and bounds; only the mirrored one samples
  # the reflection - another body reading it would show the wrong world upside down
  for i in 0 .. wb_n {
    u_f(gpu_uniform(p, "u_level"), wb_level[i])
    u_f2(gpu_uniform(p, "u_center"), wb_cx[i], wb_cz[i])
    u_f2(gpu_uniform(p, "u_extent"), wb_ex[i], wb_ez[i])
    var r = F_ZERO
    if i == wb_primary { r = ron }
    u_f(gpu_uniform(p, "u_refl_on"), r)
    # Every body is clipped to the ellipse inside its bounds but an unbounded mirrored sea,
    # whose rectangle is the point. A mirrored LAKE is clipped like any other: a map whose
    # reflection belongs to its lake (the Bells in Maroon Lake) would otherwise draw that
    # lake's level over every hollow in the survey.
    var clip = F_ONE
    if i == wb_primary and f_gt(f_max(wb_ex[i], wb_ez[i]), fi(10000)) { clip = F_ZERO }
    u_f(gpu_uniform(p, "u_clip_ellipse"), clip)
    mesh_draw(water_mesh)
  }
  gpu_blend(false)
}