# ============================================================================
# programs.ludic — GLSL from files. A shader file carries no #version line; the
# loader prepends "#version 410 core", any per-variant defines, and the shared
# noise.glsl + lighting.glsl chunks for fragment stages, then compiles it.
# ============================================================================

# Where the renderer's own files are. The shaders belong to this package and ship with
# it — in the Ludic checkout they are under packages/, and in an installed toolchain
# under $LUDIC_HOME/packages/ — so a game built outside the Ludic tree does not have to
# copy them in. The scanned CC0 materials are the other half: too large to ship with a
# toolchain and redistributable from their origin, so they are fetched into the project
# (`ludic assets`) and read from there.
# defines prepended to EVERY program (set before any is built): renderer-wide switches

function r3d_set_paths(render3d_st: mut Render3dState, root: string, assets: string) -> void { render3d_st.r3d_root = root;  render3d_st.r3d_assets = assets }

# The install root, as the compiler computes it: $LUDIC_HOME, else the directory of the
# `ludic` on PATH. A game running from its own tree finds this package there.
function r3d_home() -> string {
  let env = Os.env("LUDIC_HOME")
  if env != null and env != "" { return env }
  return `{Os.env("HOME")}/.ludic`
}

# Settle r3d_root on first use: the package as checked out beside the project, else the
# copy that ships with the toolchain.
function r3d_find_root(render3d_st: mut Render3dState) -> void {
  if render3d_st.r3d_root_found { return }
  render3d_st.r3d_root_found = true
  if Fs.exists(`{render3d_st.r3d_root}/shaders/lighting.glsl`) { return }
  let home = r3d_home()
  let alt = `{home}/packages/ludic.render3d`
  if Fs.exists(`{alt}/shaders/lighting.glsl`) { render3d_st.r3d_root = alt;  return }
  print(`r3d: cannot find the renderer's shaders (looked in {render3d_st.r3d_root}/shaders and {alt}/shaders)`)
}

function r3d_shader_file(render3d_st: mut Render3dState, name: string) -> string {
  r3d_find_root(render3d_st)
  let path = `{render3d_st.r3d_root}/shaders/{name}`
  let s = Fs.read_text(path)
  if s == null { print(`r3d: missing shader {path}`);  return "" }
  return s
}

function r3d_shader_src(render3d_st: mut Render3dState, name: string, defines: string, is_frag: bool) -> string {
  if render3d_st.r3d_noise_src == null { render3d_st.r3d_noise_src = r3d_shader_file(render3d_st, "noise.glsl") }
  if render3d_st.r3d_lighting_src == null { render3d_st.r3d_lighting_src = r3d_shader_file(render3d_st, "lighting.glsl") }
  # the wind goes to BOTH stages: the grass and the crowns move in the vertex shader, the water
  # ripples in the fragment one, and they have to be reading the same field or the meadow and
  # the lake disagree about the weather
  if render3d_st.r3d_wind_src == null { render3d_st.r3d_wind_src = r3d_shader_file(render3d_st, "wind.glsl") }
  var s = "#version 410 core\n" + render3d_st.r3d_global_defs + defines + render3d_st.r3d_wind_src
  if is_frag { s = s + render3d_st.r3d_noise_src + render3d_st.r3d_lighting_src }
  # a blade's colour field is worked out once per vertex, not once per pixel (grass.vert)
  else if Text.contains(defines, "#define GBLADE") { s = s + render3d_st.r3d_noise_src }
  return s + r3d_shader_file(render3d_st, name)
}

# Build a program from a vertex + fragment file pair (defines apply to both).
# R3D_PROGRAMS_LOG=<file>: append every program built (vertex, fragment, defines) - the list a
# backend that cannot compile shaders at run time (Vulkan: SPIR-V is built ahead) must cover
function r3d_program_log(render3d_st: mut Render3dState, vs: string, fs: string, defines: string) -> void {
  if render3d_st.r3d_prog_log < 0 { render3d_st.r3d_prog_log = 0;  if r3d_env_has(render3d_st, "R3D_PROGRAMS_LOG") { render3d_st.r3d_prog_log = 1 } }
  if render3d_st.r3d_prog_log == 0 { return }
  let f = file_open(r3d_env(render3d_st, "R3D_PROGRAMS_LOG"), "ab")
  if f == null { return }
  # one line per program: the defines' newlines become ';' so a variant is one line
  let defs = Text.replace(`{render3d_st.r3d_global_defs}{defines}`, "\n", ";")
  let line = `{vs}|{fs}|{defs}\n`
  file_write(f, line, len(line))
  file_close(f)
}
function r3d_program(render3d_st: mut Render3dState, vs: string, fs: string, defines: string) -> int {
  r3d_program_log(render3d_st, vs, fs, defines)
  let p = gpu_program(render3d_st, r3d_shader_src(render3d_st, vs, defines, false), r3d_shader_src(render3d_st, fs, defines, true), vs, fs, `{render3d_st.r3d_global_defs}{defines}`)
  if p == 0 { print(`r3d: program failed: {vs} + {fs}`) }
  return p
}

# Bind a texture to a unit and point a sampler uniform at it.
function r3d_bind_tex(render3d_st: mut Render3dState, prog: int, name: string, unit: int, kind: int, tex: int) -> void { gpu_bind_sampler(render3d_st, prog, name, unit, kind, tex) }
function r3d_bind_2d(render3d_st: mut Render3dState, prog: int, name: string, unit: int, tex: int) -> void { gpu_bind_sampler(render3d_st, prog, name, unit, GPU_TEX2D, tex) }

# A framebuffer with one colour texture (and optionally a depth texture).
property Target {
  fbo:   int = 0,
  color: int = 0,
  depth: int = 0,
  w:     int = 0,
  h:     int = 0
}
function target_new(render3d_st: mut Render3dState, w: int, h: int, ifmt: int, fmt: int, ty: int, with_depth: bool, filter: int) -> Target {
  let t = new Target
  t.w = w;  t.h = h
  t.fbo = gpu_fb_new(render3d_st)
  gpu_fb_bind(render3d_st, t.fbo)
  t.color = tex_target(render3d_st, w, h, ifmt, fmt, ty, filter)
  gpu_fb_color(render3d_st, 0, t.color)
  if with_depth {
    t.depth = tex_target(render3d_st, w, h, GL_DEPTH_COMPONENT32F, GL_DEPTH_COMPONENT, GL_FLOAT, GL_NEAREST)
    gpu_fb_depth(render3d_st, t.depth)
  }
  let st = gpu_fb_status(render3d_st)
  if st != GL_FRAMEBUFFER_COMPLETE { print(`r3d: framebuffer incomplete {st} ({w}x{h})`) }
  gpu_fb_bind(render3d_st, 0)
  return t
}
function target_free(render3d_st: mut Render3dState, t: Target) -> void {
  if t == null { return }
  gpu_fb_free(render3d_st, t.fbo)
  gpu_tex_free(render3d_st, t.color)
  if t.depth != 0 { gpu_tex_free(render3d_st, t.depth) }
}
function target_bind(render3d_st: mut Render3dState, t: Target) -> void {
  gpu_fb_bind(render3d_st, t.fbo)
  gpu_viewport(render3d_st, 0, 0, t.w, t.h)
}