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

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
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 Os.has_env("R3D_REFLDIV") { water_refl_div = Text.to_int(Os.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
  terrain_draw()
  scene_draw()
  r3d_draw_sky()
  ter_reflect = false
  sc_skip_blade = sb
  sc_freeze = false
  gpu_cull_face(GL_BACK)
  if Os.has_env("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)
}

# 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
  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
    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))
  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 but the mirrored sea is clipped to the ellipse inside its bounds
    var clip = F_ONE
    if i == wb_primary { clip = F_ZERO }
    u_f(gpu_uniform(p, "u_clip_ellipse"), clip)
    mesh_draw(water_mesh)
  }
  gpu_blend(false)
}