ludic/packages/ludic.render3d/water.ludic

# ============================================================================
# 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.
# ============================================================================

# 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.
# 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

# 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(render3d_st: mut Render3dState) -> void {
  if render3d_st.wb_primary < 0 { return }            # no body reflects: nothing to mirror
  if render3d_st.water_refl == null {
    if r3d_env_has(render3d_st, "R3D_REFLDIV") { render3d_st.water_refl_div = Text.to_int(r3d_env(render3d_st, "R3D_REFLDIV")) }
    if render3d_st.water_refl != null { target_free(render3d_st, render3d_st.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
    render3d_st.water_refl = target_new(render3d_st, render3d_st.post_w / render3d_st.water_refl_div, render3d_st.post_h / render3d_st.water_refl_div, GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT, true, GL_LINEAR)
    render3d_st.water_saved = floats(16 * 4 + 3)
    render3d_st.water_saved_vp = view(render3d_st.water_saved, 16, 16)
    render3d_st.water_saved_ivp = view(render3d_st.water_saved, 32, 16)
  }
  # save the camera
  m4_copy(render3d_st.water_saved, render3d_st.cam_view)
  m4_copy(render3d_st.water_saved_vp, render3d_st.cam_vp)
  m4_copy(render3d_st.water_saved_ivp, render3d_st.cam_inv_vp)
  let sx = render3d_st.cam_pos[0];  let sy = render3d_st.cam_pos[1];  let sz = render3d_st.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, 2.0 * render3d_st.water_level - sy, sz)
  let refl = m4_new()
  refl[5] = -1.0
  refl[13] = 2.0 * render3d_st.water_level
  let mv = floats(16)
  m4_mul(mv, render3d_st.water_saved, refl)
  m4_copy(render3d_st.cam_view, mv)
  free(mv);  free(refl)
  let fwd = words(3);  let up = words(3);  let at = words(3)
  m4_mul(render3d_st.cam_vp, render3d_st.cam_proj, render3d_st.cam_view)
  m4_inverse(render3d_st.cam_inv_vp, render3d_st.cam_vp)
  v3_copy(render3d_st.cam_pos, eye)
  render3d_st.r3d_clip_y = render3d_st.water_level - 0.05
  target_bind(render3d_st, render3d_st.water_refl)
  gpu_depth_test(render3d_st, true)
  gpu_depth_func(render3d_st, GL_LESS)
  gpu_depth_write(render3d_st, true)
  gpu_cull(render3d_st, true)
  gpu_cull_face(render3d_st, GL_FRONT)                  # the mirror flips the winding
  gpu_clear_color(render3d_st, 0.0, 0.0, 0.0, 1.0)
  gpu_clear(render3d_st, GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
  render3d_st.sc_freeze = true
  let sb = render3d_st.sc_skip_blade
  render3d_st.sc_skip_blade = true                    # blades are invisible at this scale in a reflection
  render3d_st.ter_reflect = true
  prof_cpu_mark(render3d_st, "reflection setup")
  terrain_draw(render3d_st)
  prof_cpu_mark(render3d_st, "reflection terrain")
  r3d_scene_draw(render3d_st)
  prof_cpu_mark(render3d_st, "reflection scene")
  r3d_draw_sky(render3d_st)
  prof_cpu_mark(render3d_st, "reflection sky")
  render3d_st.ter_reflect = false
  render3d_st.sc_skip_blade = sb
  render3d_st.sc_freeze = false
  gpu_cull_face(render3d_st, GL_BACK)
  if r3d_env_has(render3d_st, "R3D_DUMP_REFL") and not render3d_st.water_dumped { render3d_st.water_dumped = true;  tex_dump(render3d_st, render3d_st.water_refl.color, render3d_st.water_refl.w, render3d_st.water_refl.h, "build/dbg_refl.ppm") }
  # restore
  render3d_st.r3d_clip_y = -2147483600.0
  m4_copy(render3d_st.cam_view, render3d_st.water_saved)
  m4_copy(render3d_st.cam_vp, render3d_st.water_saved_vp)
  m4_copy(render3d_st.cam_inv_vp, render3d_st.water_saved_ivp)
  v3_set(render3d_st.cam_pos, sx, sy, sz)
  free(eye);  free(fwd);  free(up);  free(at)
  gpu_fb_bind(render3d_st, 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.
function water_reflect_visible(render3d_st: mut Render3dState) -> bool {
  if render3d_st.wb_primary < 0 { return false }
  if render3d_st.wb_refl_always < 0 { render3d_st.wb_refl_always = 0;  if r3d_env_has(render3d_st, "R3D_REFL_ALWAYS") { render3d_st.wb_refl_always = 1 } }
  if render3d_st.wb_refl_always == 1 or render3d_st.ter_heights == null { return true }
  if render3d_st.wb_ncells < 0 { let t0 = gl_now_us();  water_cells_build(render3d_st);  render3d_st.wb_build_us = gl_now_us() - t0 }
  if render3d_st.wb_dbg < 0 { render3d_st.wb_dbg = 0;  if r3d_env_has(render3d_st, "R3D_REFL_DBG") { render3d_st.wb_dbg = 1 } }
  if render3d_st.wb_dbg == 1 {
    # R3D_REFL_DBG: once, what the test is made of and how much of it is in view
    render3d_st.wb_dbg = 2
    var seen = 0
    var hidden = 0
    for i in 0 .. render3d_st.wb_ncells { if wb_cell_visible(render3d_st, i) { seen += 1;  if wb_cell_occluded(render3d_st, i) { hidden += 1 } } }
    print(`water reflection test: {render3d_st.wb_ncells} wet rectangles in {render3d_st.wb_nblocks} blocks (built in {render3d_st.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 .. render3d_st.wb_nblocks {
    let o = b * 6
    if not wb_rect_visible(render3d_st, float_from_bits(render3d_st.wb_blocks[o]), float_from_bits(render3d_st.wb_blocks[o + 1]), float_from_bits(render3d_st.wb_blocks[o + 2]), float_from_bits(render3d_st.wb_blocks[o + 3])) { continue }
    for i in render3d_st.wb_blocks[o + 4] .. render3d_st.wb_blocks[o + 5] {
      if not wb_cell_visible(render3d_st, i) { continue }
      if checked >= 16 { return true }
      checked += 1
      if not wb_cell_occluded(render3d_st, 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(render3d_st: Render3dState, x0: float, z0: float, x1: float, z1: float) -> bool {
  if render3d_st.cam_planes == null { return true }
  for p in 0 .. 4 {
    let q = p * 4
    let a = render3d_st.cam_planes[q];  let c = render3d_st.cam_planes[q + 2]
    let by = render3d_st.cam_planes[q + 1] * render3d_st.water_level + render3d_st.cam_planes[q + 3]
    let ax0 = a * x0;  let ax1 = a * x1;  let cz0 = c * z0;  let cz1 = c * z1
    if ax0 + cz0 + by < 0.0 and ax1 + cz0 + by < 0.0 and ax0 + cz1 + by < 0.0 and ax1 + cz1 + by < 0.0 { return false }
  }
  return true
}
function wb_cell_visible(render3d_st: Render3dState, i: int) -> bool {
  let o = i * 4
  return wb_rect_visible(render3d_st, render3d_st.wb_cells[o], render3d_st.wb_cells[o + 1], render3d_st.wb_cells[o + 2], render3d_st.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(render3d_st: mut Render3dState, x: float, z: float) -> bool {
  if terrain_height(render3d_st, x, z) > render3d_st.water_level + 0.05 { return true }
  if not cam_sphere_visible(render3d_st, x, render3d_st.water_level, z, 0.5) { return true }
  let ey = render3d_st.cam_pos[1]
  if not (ey > render3d_st.water_level) { return false }
  let dx = x - render3d_st.cam_pos[0];  let dz = z - render3d_st.cam_pos[2]
  let margin = 0.5 + Math.sqrt(dx * dx + dz * dz) * 0.004
  for k in 1 .. 8 {
    let t = float(k) / 8.0
    let sy = ey + (render3d_st.water_level - ey) * t
    if terrain_height(render3d_st, render3d_st.cam_pos[0] + dx * t, render3d_st.cam_pos[2] + dz * t) > 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(render3d_st: mut Render3dState, i: int) -> bool {
  let o = i * 4
  let x0 = render3d_st.wb_cells[o];  let z0 = render3d_st.wb_cells[o + 1];  let x1 = render3d_st.wb_cells[o + 2];  let z1 = render3d_st.wb_cells[o + 3]
  let cx = (x0 + x1) * 0.5;  let cz = (z0 + z1) * 0.5
  let ox = (x1 - x0) * 0.45;  let oz = (z1 - z0) * 0.45
  if not wb_point_hidden(render3d_st, cx, cz) { return false }
  if not wb_point_hidden(render3d_st, cx - ox, cz - oz) { return false }
  if not wb_point_hidden(render3d_st, cx + ox, cz - oz) { return false }
  if not wb_point_hidden(render3d_st, cx - ox, cz + oz) { return false }
  return wb_point_hidden(render3d_st, cx + ox, cz + oz)
}
function wb_cell_add(render3d_st: mut Render3dState, x0: float, z0: float, x1: float, z1: float) -> void {
  let o = render3d_st.wb_ncells * 4
  render3d_st.wb_cells[o] = x0;  render3d_st.wb_cells[o + 1] = z0;  render3d_st.wb_cells[o + 2] = x1;  render3d_st.wb_cells[o + 3] = z1
  render3d_st.wb_ncells += 1
}
function wb_block_add(render3d_st: mut Render3dState, x0: float, z0: float, x1: float, z1: float, first: int) -> void {
  if render3d_st.wb_ncells <= first { return }
  let o = render3d_st.wb_nblocks * 6
  render3d_st.wb_blocks[o] = float_bits(x0);  render3d_st.wb_blocks[o + 1] = float_bits(z0);  render3d_st.wb_blocks[o + 2] = float_bits(x1);  render3d_st.wb_blocks[o + 3] = float_bits(z1)
  render3d_st.wb_blocks[o + 4] = first;  render3d_st.wb_blocks[o + 5] = render3d_st.wb_ncells
  render3d_st.wb_nblocks += 1
}
function wb_wet(render3d_st: mut Render3dState, x: float, z: float, off: float) -> bool {
  if terrain_height(render3d_st, x, z) < render3d_st.water_level { return true }
  if off == 0.0 { return false }
  if terrain_height(render3d_st, x - off, z - off) < render3d_st.water_level { return true }
  if terrain_height(render3d_st, x + off, z - off) < render3d_st.water_level { return true }
  if terrain_height(render3d_st, x - off, z + off) < render3d_st.water_level { return true }
  return terrain_height(render3d_st, x + off, z + off) < render3d_st.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
@alloc_ok("a world being set up (a stream, a layer, water, post, a bake): the map loading or swapping, not a frame")
function water_cells_build(render3d_st: mut Render3dState) -> void {
  let bx0 = render3d_st.water_cx - render3d_st.water_ex;  let bx1 = render3d_st.water_cx + render3d_st.water_ex
  let bz0 = render3d_st.water_cz - render3d_st.water_ez;  let bz1 = render3d_st.water_cz + render3d_st.water_ez
  let th = float(render3d_st.TERRAIN_HALF)
  let tx0 = Math.max(bx0, render3d_st.ter_ox - th);  let tx1 = Math.min(bx1, render3d_st.ter_ox + th)
  let tz0 = Math.max(bz0, render3d_st.ter_oz - th);  let tz1 = Math.min(bz1, render3d_st.ter_oz + th)
  let inside = tx1 > tx0 and tz1 > tz0
  var cell = 32.0
  var nx = 0
  var nz = 0
  if inside {
    let span = Math.max(tx1 - tx0, tz1 - tz0)
    if span / cell > 512.0 { cell = span / 512.0 }
    nx = int((tx1 - tx0) / cell) + 1
    nz = int((tz1 - tz0) / cell) + 1
  }
  if render3d_st.wb_cells != null { free(render3d_st.wb_cells) }
  if render3d_st.wb_blocks != null { free(render3d_st.wb_blocks) }
  render3d_st.wb_cells = floats((nx * nz + 64 * 64) * 4)
  let nbx = (nx + WB_BLOCK - 1) / WB_BLOCK
  let nbz = (nz + WB_BLOCK - 1) / WB_BLOCK
  render3d_st.wb_blocks = words((nbx * nbz + 1) * 6)
  render3d_st.wb_ncells = 0
  render3d_st.wb_nblocks = 0
  let off = cell * 0.45
  let half = cell * 0.5
  for bz in 0 .. nbz {
    for bx in 0 .. nbx {
      let first = render3d_st.wb_ncells
      var iz = bz * WB_BLOCK
      while iz < (bz + 1) * WB_BLOCK and iz < nz {
        let z0 = tz0 + float(iz) * cell
        var ix = bx * WB_BLOCK
        while ix < (bx + 1) * WB_BLOCK and ix < nx {
          let x0 = tx0 + float(ix) * cell
          if wb_wet(render3d_st, x0 + half, z0 + half, off) { wb_cell_add(render3d_st, x0, z0, x0 + cell, z0 + cell) }
          ix += 1
        }
        iz += 1
      }
      let x0 = tx0 + float(bx * WB_BLOCK) * cell;  let z0 = tz0 + float(bz * WB_BLOCK) * cell
      wb_block_add(render3d_st, x0, z0, x0 + float(WB_BLOCK) * cell, z0 + float(WB_BLOCK) * cell, first)
    }
  }
  let first = render3d_st.wb_ncells
  let cw = (bx1 - bx0) / 64.0
  let ch = (bz1 - bz0) / 64.0
  for iz in 0 .. 64 {
    let z0 = bz0 + float(iz) * ch;  let z1 = z0 + ch
    for ix in 0 .. 64 {
      let x0 = bx0 + float(ix) * cw;  let x1 = x0 + cw
      # inside the height map's rectangle: the fine cells above cover it
      if inside and not (x0 < tx0) and not (x1 > tx1) and not (z0 < tz0) and not (z1 > tz1) { continue }
      if wb_wet(render3d_st, x0 + cw * 0.5, z0 + ch * 0.5, 0.0) { wb_cell_add(render3d_st, x0, z0, x1, z1) }
    }
  }
  wb_block_add(render3d_st, bx0, bz0, bx1, bz1, first)
}

# the program and the plane are the process's, built once; the bodies are the map's
@alloc_ok("a world being set up (a stream, a layer, water, post, a bake): the map loading or swapping, not a frame")
function water_setup(render3d_st: mut Render3dState) -> void {
  if render3d_st.water_prog != 0 { return }
  render3d_st.water_mesh = mesh_grid(render3d_st, 2, 0.5)
  render3d_st.water_prog = r3d_program(render3d_st, "water.vert", "water.frag", "")
  render3d_st.wb_level = floats(WATER_MAX);  render3d_st.wb_cx = floats(WATER_MAX);  render3d_st.wb_cz = floats(WATER_MAX)
  render3d_st.wb_ex = floats(WATER_MAX);  render3d_st.wb_ez = floats(WATER_MAX);  render3d_st.wb_reflect = words(WATER_MAX)
}
function water_bodies_clear(render3d_st: mut Render3dState) -> void {
  render3d_st.wb_n = 0
  render3d_st.wb_primary = -1
  render3d_st.wb_ncells = -1
  render3d_st.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(render3d_st: mut Render3dState, level: float, cx: float, cz: float, ex: float, ez: float, reflect: bool) -> int {
  water_setup(render3d_st)
  if render3d_st.wb_n >= WATER_MAX { return -1 }
  let i = render3d_st.wb_n
  render3d_st.wb_level[i] = level;  render3d_st.wb_cx[i] = cx;  render3d_st.wb_cz[i] = cz;  render3d_st.wb_ex[i] = ex;  render3d_st.wb_ez[i] = ez
  render3d_st.wb_reflect[i] = 0
  if reflect { render3d_st.wb_reflect[i] = 1 }
  render3d_st.wb_n += 1
  render3d_st.water_on = true
  if reflect and render3d_st.wb_primary < 0 {
    render3d_st.wb_primary = i
    render3d_st.wb_ncells = -1
    render3d_st.water_level = level;  render3d_st.water_cx = cx;  render3d_st.water_cz = cz;  render3d_st.water_ex = ex;  render3d_st.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(render3d_st: mut Render3dState, level: float, cx: float, cz: float, ex: float, ez: float) -> void {
  water_bodies_clear(render3d_st)
  water_body_add(render3d_st, level, cx, cz, ex, ez, true)
}

# call after the opaque pass, before the sky: blends over the resolved depth
function water_draw(render3d_st: mut Render3dState, depth_tex: int) -> void {
  if not render3d_st.water_on or render3d_st.wb_n == 0 { return }
  let p = render3d_st.water_prog
  gpu_use_program(render3d_st, p)
  u_mat4(render3d_st, gpu_uniform(render3d_st, p, "u_view"), render3d_st.cam_view)
  u_mat4(render3d_st, gpu_uniform(render3d_st, p, "u_proj"), render3d_st.cam_proj)
  u_mat4(render3d_st, gpu_uniform(render3d_st, p, "u_inv_vp"), render3d_st.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(render3d_st, gpu_uniform(render3d_st, p, "u_screen"), float(render3d_st.post_w), float(render3d_st.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 = render3d_st.wt_wade_x
  let wz = render3d_st.wt_wade_z
  let ws = render3d_st.wt_wade_s
  u_f3(render3d_st, gpu_uniform(render3d_st, p, "u_wade"), wx, wz, ws)
  var ron = 0.0
  if render3d_st.water_refl != null and render3d_st.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(render3d_st, p, "u_refl", 1, render3d_st.water_refl.color);  ron = 1.0
    # the parameter and the chain are the BOUND texture's, and binding a sampler by name does not
    # bind it: without this they went to whatever was bound last - a BC7 kit texture since 23.3,
    # which the mip blits then drew into (Metal: "BC7 is not color renderable")
    gpu_tex_bind(render3d_st, GPU_TEX2D, render3d_st.water_refl.color)
    gpu_tex_param(render3d_st, GPU_TEX2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR)
    gpu_tex_mips(render3d_st, GPU_TEX2D)
  }
  r3d_bind_2d(render3d_st, p, "u_depth", 0, depth_tex)
  r3d_bind_2d(render3d_st, p, "u_scene", 2, render3d_st.post_scene.color)
  sky_bind_lighting(render3d_st, p)
  shadow_bind(render3d_st, p)
  fog_bind(render3d_st, 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(render3d_st, false)
  gpu_blend_func(render3d_st, 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(render3d_st, true)
  gpu_cull(render3d_st, 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 .. render3d_st.wb_n {
    u_f(render3d_st, gpu_uniform(render3d_st, p, "u_level"), render3d_st.wb_level[i])
    u_f2(render3d_st, gpu_uniform(render3d_st, p, "u_center"), render3d_st.wb_cx[i], render3d_st.wb_cz[i])
    u_f2(render3d_st, gpu_uniform(render3d_st, p, "u_extent"), render3d_st.wb_ex[i], render3d_st.wb_ez[i])
    var r = 0.0
    if i == render3d_st.wb_primary { r = ron }
    u_f(render3d_st, gpu_uniform(render3d_st, 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 = 1.0
    if i == render3d_st.wb_primary and Math.max(render3d_st.wb_ex[i], render3d_st.wb_ez[i]) > 10000.0 { clip = 0.0 }
    u_f(render3d_st, gpu_uniform(render3d_st, p, "u_clip_ellipse"), clip)
    mesh_draw(render3d_st, render3d_st.water_mesh)
  }
  gpu_blend(render3d_st, false)
}