# ============================================================================
# post.ludic — the HDR frame and what happens to it: a 16-bit float scene
# target, a mip-chain bloom (13-tap down, tent up), and the tonemap composite
# (exposure, ACES, vignette, saturation, contrast, dither) to the screen.
# ============================================================================

const BLOOM_LEVELS: int = 6

var post_hdr: Target = null
var post_ms_fbo: int = 0          # 4x multisampled scene target, resolved into post_hdr
var post_ms_samples: int = 1      # temporal AA carries the edges; R3D_MSAA=n to compare
var post_bloom: []Target = null
var post_p_down: int = 0
var post_p_up: int = 0
var post_p_tone: int = 0
var post_fs: Mesh = null
var post_exposure: int = 0
var post_bloom_strength: int = 0
var post_vignette: int = 0
var post_saturation: int = 0
var post_contrast: int = 0
var post_w: int = 0
var post_h: int = 0
var post_auto: bool = true
var post_key: int = 0             # target mean luminance after exposure (float bits)
var post_lum: words = null
var post_mips: int = 0
var post_adapt: int = 0           # smoothed exposure (float bits)
var post_exposure_max: int = 0x41A00000   # 20: the ceiling auto-exposure may reach (night lowers it)

var post_ao: Target = null
var post_ao_blur: Target = null
var post_p_ao: int = 0
var post_p_ao_blur: int = 0
var post_ao_radius: int = 0
var post_ao_intensity: int = 0
var post_ao_strength: int = 0
var post_gi_strength: int = 0x3ECCCCCD     # 0.4
var post_no_gi: bool = false
var post_ldr: Target = null
var post_depth_copy: Target = null
var post_prev: Target = null       # last frame's scene colour, for the SSGI bounce only
var post_scene: Target = null      # this frame's scene colour before the water, for refraction
var post_frame: int = 0
var post_color_w: int = 0          # its size: the display's when DLSS upscaled it
var post_color_h: int = 0
var post_color: int = 0            # the HDR colour the rest of post reads      # the resolved depth, copied so passes can read it while drawing into the frame
var post_p_sharp: int = 0
var post_p_tone_hdr: int = 0        # the tonemap's HDR10 variant, made the first time HDR is on
var post_ldr_hdr: bool = false       # post_ldr was made for HDR10 output (10-bit)
# the LDR image is 10-bit while the output is HDR10: PQ in 8 bits bands
function post_ldr_fmt() -> int { if gpu_hdr_active() { return GL_RGB10_A2 };  return GL_RGBA8 }
var post_sharpen: int = 0
var post_grain: int = 0

# the screen-sized targets go away before post_init makes them at a new size
function post_free() -> void {
  if post_hdr == null { return }
  if post_ms_fbo != 0 { gpu_fb_free(post_ms_fbo);  post_ms_fbo = 0 }
  target_free(post_hdr);  target_free(post_ao);  target_free(post_ao_blur);  target_free(post_ldr)
  target_free(post_depth_copy);  target_free(post_prev);  target_free(post_scene)
  for i in 0 .. len(post_bloom) { target_free(post_bloom[i]) }
  post_hdr = null
}
# Multisampled scene: 1 (temporal AA alone), 2 or 4, remade at once. Vulkan draws it into
# multisampled renderbuffers and resolves them in a pass; a device that cannot take the count asked
# for gets the most it can (gpu_msaa_max).
function post_msaa_live() -> bool { return gpu_is_gl() or gpu_msaa_max() > 1 }
function post_set_msaa(n: int) -> void {
  var want = n
  if want < 1 { want = 1 }
  if not post_msaa_live() { want = 1 }
  if want > gpu_msaa_max() and gpu_msaa_max() >= 1 { want = gpu_msaa_max() }
  if want == post_ms_samples { return }
  post_ms_samples = want
  if post_hdr != null {
    let w = post_w;  let h = post_h
    post_free()
    post_init(w, h)
  }
}

function post_init(w: int, h: int) -> void {
  post_w = w;  post_h = h
  post_hdr = target_new(w, h, GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT, true, GL_LINEAR)
  if post_ms_samples > 1 {
    post_ms_fbo = gpu_fb_new()
    gpu_fb_bind(post_ms_fbo)
    let rbc = gpu_rb_new()
    gpu_rb_storage(rbc, GL_RGBA16F, w, h, post_ms_samples)
    gpu_fb_color_rb(0, rbc)
    let rbd = gpu_rb_new()
    gpu_rb_storage(rbd, GL_DEPTH_COMPONENT32F, w, h, post_ms_samples)
    gpu_fb_depth_rb(rbd)
    let st = gpu_fb_status()
    if st != GL_FRAMEBUFFER_COMPLETE { print(`r3d: msaa framebuffer incomplete {st}`);  post_ms_fbo = 0 }
    gpu_fb_bind(0)
  }
  post_bloom = new []Target
  var bw = w / 2;  var bh = h / 2
  for i in 0 .. BLOOM_LEVELS {
    push(post_bloom, target_new(max(bw, 1), max(bh, 1), GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT, false, GL_LINEAR))
    bw = bw / 2;  bh = bh / 2
  }
  if post_p_down == 0 {
    post_p_down = r3d_program("fullscreen.vert", "bloom_down.frag", "")
    post_p_up = r3d_program("fullscreen.vert", "bloom_up.frag", "")
    post_p_tone = r3d_program("fullscreen.vert", "tonemap.frag", "")
  }
  # Full resolution, not half. The occlusion is reconstructed from depth differences,
  # so on a surface seen at a grazing angle its gradient is steep in screen space; at
  # half resolution that aliased into wide, screen-crossing bands which the bilinear
  # upsample in the tonemapper then stretched over the whole ground. They read as thin
  # transparent black bars, appear only where there is depth (never on the sky), and
  # are nothing to do with the shadow map or the reflection.
  post_ao = target_new(w, h, GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT, false, GL_LINEAR)
  post_ao_blur = target_new(w, h, GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT, false, GL_LINEAR)
  if post_p_ao == 0 { post_p_ao = r3d_program("fullscreen.vert", "ssgi.frag", "");  post_p_ao_blur = r3d_program("fullscreen.vert", "ssao_blur.frag", "") }
  post_ldr = target_new(w, h, post_ldr_fmt(), GL_RGBA, GL_UNSIGNED_BYTE, false, GL_LINEAR)
  post_ldr_hdr = gpu_hdr_active()
  post_depth_copy = target_new(w, h, GL_R8, GL_RED, GL_UNSIGNED_BYTE, true, GL_NEAREST)
  post_prev = target_new(w, h, GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT, false, GL_LINEAR)
  post_scene = target_new(w, h, GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT, false, GL_LINEAR)
  if post_p_sharp == 0 { post_p_sharp = r3d_program("fullscreen.vert", "sharpen.frag", "") }
  post_sharpen = fl(1.2)
  post_grain = fl(0.025)
  post_ao_radius = fl(0.7)
  post_ao_intensity = fl(1.4)
  post_ao_strength = fl(0.8)
  post_fs = mesh_fullscreen()
  post_exposure = fl(0.36)
  post_bloom_strength = fl(0.06)
  post_vignette = fl(0.35)
  post_saturation = fl(1.04)
  post_contrast = fl(1.12)
  post_key = fl(0.19)
  post_lum = words(4)
  var m = 1;  var sz = max(w, h)
  while sz > 1 { sz = sz / 2;  m += 1 }
  post_mips = m
  post_adapt = F_ZERO
}

# Mean scene luminance from the HDR mip chain -> exposure = key / mean, eased over
# frames. The value comes back through a pixel buffer one frame late: a direct
# glGetTexImage waits for the GPU to finish the whole frame, which serialised the
# CPU and the GPU. With the fly-camera demo that cost little (the CPU had nothing
# else to do); with the game's animals, HUD and rules on the CPU it doubled the frame
# (60 ms -> 28 ms when the read went asynchronous, measured 2026-09-09).
# ... and even that asynchronous read blocked on Apple's GL (glGetTexImage into a pixel
# buffer still synchronised the texture: 50% of the CPU's frame waiting, sampled), so
# the adaptation now stays on the GPU: a 1x1 pass (adapt.frag) eases last frame's value
# toward key / mean and the tonemapper samples it. The CPU never waits for the picture.
var post_adapt_t: []Target = null
var post_adapt_i: int = 0
var post_p_adapt: int = 0
var post_adapt_reset: bool = true
function post_measure() -> void {
  gpu_tex_bind(GPU_TEX2D, post_hdr.color)
  gpu_tex_param(GPU_TEX2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR)
  gpu_tex_mips(GPU_TEX2D)
  if post_adapt_t == null {
    post_adapt_t = new []Target
    for k in 0 .. 2 { push(post_adapt_t, target_new(1, 1, GL_R32F, GL_RED, GL_FLOAT, false, GL_NEAREST)) }
    post_adapt_reset = true
  }
  if post_p_adapt == 0 { post_p_adapt = r3d_program("fullscreen.vert", "adapt.frag", "") }
  let next = 1 - post_adapt_i
  target_bind(post_adapt_t[next])
  gpu_depth_test(false)
  gpu_use_program(post_p_adapt)
  r3d_bind_2d(post_p_adapt, "u_scene", 0, post_hdr.color)
  r3d_bind_2d(post_p_adapt, "u_prev", 1, post_adapt_t[post_adapt_i].color)
  u_f(gpu_uniform(post_p_adapt, "u_lod"), fi(post_mips - 1))
  u_f(gpu_uniform(post_p_adapt, "u_key"), post_key)
  u_f(gpu_uniform(post_p_adapt, "u_max"), post_exposure_max)
  u_f(gpu_uniform(post_p_adapt, "u_rate"), fl(0.08))
  var reset = F_ZERO
  if post_adapt_reset { reset = F_ONE;  post_adapt_reset = false }
  u_f(gpu_uniform(post_p_adapt, "u_reset"), reset)
  mesh_draw(post_fs)
  post_adapt_i = next
  gpu_tex_bind(GPU_TEX2D, post_hdr.color)
  gpu_tex_param(GPU_TEX2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
}

function post_begin_scene() -> void {
  target_bind(post_hdr)
  if post_ms_fbo != 0 { gpu_fb_bind(post_ms_fbo);  gpu_multisample(true) }
  gpu_depth_test(true)
  gpu_depth_func(GL_LESS)
  gpu_depth_write(true)
  gpu_cull(true)
  gpu_cull_face(GL_BACK)
  gpu_clear_color(0.0, 0.0, 0.0, 1.0)
  gpu_clear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
}

# resolve the multisampled scene into the plain HDR target (colour + depth)
function post_resolve() -> void {
  if post_ms_fbo != 0 {
    gpu_fb_bind_read(post_ms_fbo)
    gpu_fb_bind_draw(post_hdr.fbo)
    gpu_blit(post_w, post_h, GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
  }
  # the depth copy every pass after this may read while the frame is still being drawn into
  gpu_fb_bind_read(post_hdr.fbo)
  gpu_fb_bind_draw(post_depth_copy.fbo)
  gpu_blit(post_w, post_h, GL_DEPTH_BUFFER_BIT)
  gpu_fb_bind(0)
}

# There is no temporal anti-aliasing. It was reprojecting every pixel through the
# scene depth, which on water is the surface plane while the pixel's content is the
# reflection behind it — so the mirror image was fetched from the wrong place and, at
# 0.92 history, dragged several frames behind the camera as it turned. Geometry edges
# and the alpha-tested vegetation are covered by the 4x MSAA + alpha-to-coverage the
# scene already renders with, and the projection is no longer jittered, so nothing is
# left needing a temporal resolve.

# The lake bed, as drawn, before any water goes over it. Water reads this to refract and
# then absorb it, which is what makes the surface read as a body of water rather than a
# sheet laid over the ground: the bottom is seen THROUGH the water, tinted and dimmed by
# how far the light travelled, instead of being the dry terrain showing through an alpha.
function post_capture_scene() -> void {
  gpu_fb_bind_read(post_hdr.fbo)
  gpu_fb_bind_draw(post_scene.fbo)
  gpu_blit(post_w, post_h, GL_COLOR_BUFFER_BIT)
  gpu_fb_bind(post_hdr.fbo)
  gpu_viewport(0, 0, post_w, post_h)
}

# Keep a copy of the finished scene colour: the SSGI bounce reads last frame's colour.
function post_capture_prev() -> void {
  gpu_fb_bind_read(post_hdr.fbo)
  gpu_fb_bind_draw(post_prev.fbo)
  gpu_blit(post_w, post_h, GL_COLOR_BUFFER_BIT)
  gpu_fb_bind(0)
  post_frame += 1
}

function post_ssao_pass() -> void {
  gpu_depth_test(false)
  gpu_blend(false)
  target_bind(post_ao)
  gpu_use_program(post_p_ao)
  r3d_bind_2d(post_p_ao, "u_depth", 0, post_hdr.depth)
  r3d_bind_2d(post_p_ao, "u_prev_color", 1, post_prev.color)
  u_f(gpu_uniform(post_p_ao, "u_frame"), fi(post_frame % 64))
  u_mat4(gpu_uniform(post_p_ao, "u_inv_proj"), cam_inv_proj)
  u_mat4(gpu_uniform(post_p_ao, "u_proj"), cam_proj)
  u_f2(gpu_uniform(post_p_ao, "u_texel"), fr(1, post_w), fr(1, post_h))
  u_f(gpu_uniform(post_p_ao, "u_radius"), post_ao_radius)
  u_f(gpu_uniform(post_p_ao, "u_intensity"), post_ao_intensity)
  mesh_draw(post_fs)
  target_bind(post_ao_blur)
  gpu_use_program(post_p_ao_blur)
  r3d_bind_2d(post_p_ao_blur, "u_ao", 0, post_ao.color)
  r3d_bind_2d(post_p_ao_blur, "u_depth", 1, post_hdr.depth)
  u_f2(gpu_uniform(post_p_ao_blur, "u_texel"), fr(1, post_ao.w), fr(1, post_ao.h))
  mesh_draw(post_fs)
}

function post_bloom_pass() -> void {
  gpu_depth_test(false)
  gpu_blend(false)
  var src = post_color
  var sw = post_color_w;  var sh = post_color_h
  gpu_use_program(post_p_down)
  for i in 0 .. BLOOM_LEVELS {
    let t = post_bloom[i]
    target_bind(t)
    r3d_bind_2d(post_p_down, "u_src", 0, src)
    u_f2(gpu_uniform(post_p_down, "u_texel"), fr(1, sw), fr(1, sh))
    var th = f_neg1()
    if i == 0 { th = fl(1.2) }
    u_f(gpu_uniform(post_p_down, "u_threshold"), th)
    mesh_draw(post_fs)
    src = t.color;  sw = t.w;  sh = t.h
  }
  gpu_use_program(post_p_up)
  gpu_blend(true)
  gpu_blend_func(GL_ONE, GL_ONE)
  var i = BLOOM_LEVELS - 1
  while i > 0 {
    let from = post_bloom[i]
    let to = post_bloom[i - 1]
    target_bind(to)
    r3d_bind_2d(post_p_up, "u_src", 0, from.color)
    u_f2(gpu_uniform(post_p_up, "u_texel"), fr(1, from.w), fr(1, from.h))
    u_f(gpu_uniform(post_p_up, "u_radius"), F_ONE)
    mesh_draw(post_fs)
    i -= 1
  }
  gpu_blend(false)
}

function post_tonemap(color_tex: int) -> void {
  var prog = post_p_tone
  if gpu_hdr_active() {
    if post_p_tone_hdr == 0 { post_p_tone_hdr = r3d_program("fullscreen.vert", "tonemap.frag", "#define HDR10\n") }
    prog = post_p_tone_hdr
  }
  if post_ldr_hdr != gpu_hdr_active() {
    let w = post_ldr.w;  let h = post_ldr.h
    target_free(post_ldr)
    post_ldr = target_new(w, h, post_ldr_fmt(), GL_RGBA, GL_UNSIGNED_BYTE, false, GL_LINEAR)
    post_ldr_hdr = gpu_hdr_active()
  }
  if post_auto { post_measure() }
  target_bind(post_ldr)
  gpu_depth_test(false)
  gpu_use_program(prog)
  r3d_bind_2d(prog, "u_hdr", 0, color_tex)
  r3d_bind_2d(prog, "u_bloom", 1, post_bloom[0].color)
  r3d_bind_2d(prog, "u_ao", 2, post_ao_blur.color)
  u_f(gpu_uniform(prog, "u_ao_strength"), post_ao_strength)
  u_f(gpu_uniform(prog, "u_gi_strength"), post_gi_strength)
  u_f(gpu_uniform(prog, "u_exposure"), post_exposure)
  var auto = F_ZERO
  if post_auto and post_adapt_t != null { auto = F_ONE;  r3d_bind_2d(prog, "u_adapt", 3, post_adapt_t[post_adapt_i].color) }
  u_f(gpu_uniform(prog, "u_auto"), auto)
  u_f(gpu_uniform(prog, "u_bloom_strength"), post_bloom_strength)
  u_f(gpu_uniform(prog, "u_vignette"), post_vignette)
  u_f(gpu_uniform(prog, "u_saturation"), post_saturation)
  u_f(gpu_uniform(prog, "u_contrast"), post_contrast)
  u_f3(gpu_uniform(prog, "u_wb"), fl(1.02), F_ONE, fl(0.97))
  u_f3(gpu_uniform(prog, "u_lift"), fl(0.004), fl(0.004), fl(0.012))
  u_f3(gpu_uniform(prog, "u_gain"), fl(0.99), fl(0.995), fl(1.0))
  # the HDR10 variant's display calibration (the SDR program has none of these, and -1 sets nothing)
  u_f(gpu_uniform(prog, "u_hdr_peak"), r3d_hdr_peak_nits())
  u_f(gpu_uniform(prog, "u_hdr_paper"), r3d_hdr_paper_nits())
  u_f(gpu_uniform(prog, "u_hdr_black"), r3d_hdr_black_nits())
  mesh_draw(post_fs)
  # sharpen + grain onto the screen
  gpu_fb_bind(gpu_screen_fb())
  gpu_viewport(0, 0, gl_w, gl_h)
  gpu_use_program(post_p_sharp)
  r3d_bind_2d(post_p_sharp, "u_src", 0, post_ldr.color)
  u_f2(gpu_uniform(post_p_sharp, "u_texel"), fr(1, post_ldr.w), fr(1, post_ldr.h))
  u_f(gpu_uniform(post_p_sharp, "u_amount"), post_sharpen)
  # R3D_NOGRAIN=1: no film grain, so two frames of a still camera can be compared for what else moves
  var grain = post_grain
  if r3d_env_has("R3D_NOGRAIN") { grain = F_ZERO }
  u_f(gpu_uniform(post_p_sharp, "u_grain"), grain)
  u_f(gpu_uniform(post_p_sharp, "u_time"), r3d_time)
  mesh_draw(post_fs)
}