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Demo / attract mode (shareware)

This page documents the classic shareware demo/attract loop implemented in crimsonland.exe. The same code exists in the v1.9.93 codebase but is normally gated by game_is_full_version() (the DRM-free builds don’t enter the loop on their own).

The demo loop is useful for reimplementation because it exercises:

  • Gameplay state 9 (creatures/projectiles/players) without needing menu work.
  • A deterministic set of setup variants (demo_setup_variant_*).
  • A self-contained “upsell” overlay that drives a timer and transitions back to menu state 0 (classic behavior; out of scope for our rewrite, since the storefront is defunct).

Entry points

Boot handoff: logos → demo

In the logo sequence, once the logo timer passes the theme trigger (~14s), the shareware build:

  • mutes the intro track
  • plays music_track_crimsonquest_id
  • calls demo_mode_start() (0x00403390)

Full builds instead play music_track_crimson_theme_id and proceed to the menu.

See: docs/boot-sequence.md (handoff section).

Runtime entry: trial/attract trigger

The main loop (console_hotkey_update) contains a shareware-only path that starts demo_mode_start() and switches music to shortie_monk (exact trigger still TBD; see decompile around 0x0040cf06).

Core loop model

At a high level:

  • Demo mode runs in gameplay state 9.
  • demo_mode_active gates HUD and input behavior.
  • demo_mode_start() resets the session and picks a setup variant.
  • A per-frame overlay (demo_purchase_screen_update) is rendered on top and can transition to menu state 0.

Main loop integration (state 9)

In the per-frame dispatcher:

  • If game_state_id == 9:
  • If demo_purchase_screen_active is 0: run gameplay_update_and_render().
  • Else: skip gameplay and clear the screen.
  • If demo_mode_active != 0: always run demo_purchase_screen_update() on top.

This is why the demo cycle includes a “purchase interstitial” variant: it flips demo_purchase_screen_active to suppress gameplay and show only the upsell screen for a fixed time. In the rewrite, the interstitial + upsell overlay are intentionally skipped; the loop cycles gameplay variants and returns to menu.

Timing: quest_spawn_timeline + demo_time_limit_ms

Two globals define the cycle timing:

  • quest_spawn_timeline (0x00486fd0): a generic “mode timeline” counter (ms). Reset to 0 by demo_mode_start().
  • demo_time_limit_ms (0x004712f0): demo timer limit used as:
  • ~4–5s per gameplay variant (4000/5000)
  • ~10s for the interstitial (10000)
  • ~16s when the user triggers the purchase screen (16000)

Mode-specific update hooks use these:

  • survival_update() and rush_mode_update():
  • if demo_mode_active and quest_spawn_timeline > demo_time_limit_ms: call demo_mode_start().
  • demo_purchase_screen_update():
  • when the purchase screen is active, it increments quest_spawn_timeline itself and restarts via demo_mode_start() when it exceeds demo_time_limit_ms.

demo_mode_start (0x00403390)

High-confidence pseudocode (decompile + callsite xrefs):

if (game_state_id != 9) game_state_set(9);

demo_purchase_screen_active = 0;
demo_mode_active = 1;

gameplay_reset_state();
config.game_mode = 1; // survival

switch (demo_variant_index) {
  case 0: demo_setup_variant_0(); break;
  case 1: demo_setup_variant_1(); break;
  case 2: demo_setup_variant_2(); break;
  case 3: demo_setup_variant_3(); break;
  case 4: demo_setup_variant_0(); break;
  case 5: demo_purchase_interstitial_begin(); break; // 0x00403370
}

quest_spawn_timeline = 0;
screen_fade_ramp_flag = 0; // DAT_0048702c
demo_variant_index = (demo_variant_index + 1) % 6;

Setup variants (demo_setup_variant_*)

The variants are small, deterministic setup functions that:

  • set config.player_count
  • optionally call terrain_generate(desc)
  • spawn a fixed set of creatures via creature_spawn_template(spawn_id, pos_xy, heading)
  • position players and assign starting weapons
  • set demo_time_limit_ms

Variant 0 — demo_setup_variant_0 (0x00402ed0)

  • player_count = 2
  • demo_time_limit_ms = 4000
  • Spawns template 0x38 in two columns (x≈128/192 and x≈798/862), y=256..1632 step 80.
  • Player positions: P1 (448,384), P2 (546,654).
  • Weapon: 0x0b (Rocket Launcher) for both.
  • Uses heading = -100.0 for spawns (likely a sentinel; exact semantics TBD).

Variant 1 — demo_setup_variant_1 (0x004030f0)

  • player_count = 2
  • terrain_generate(&DAT_00484914) (this points into the quest metadata table; see docs/crimsonland-exe/terrain.md).
  • demo_time_limit_ms = 5000
  • Spawns 20× template 0x34 plus ~13× template 0x35 at random positions:
  • x = rand()%200 + 32 (or %30 + 32 for template 0x35)
  • y = rand()%899 + 64
  • heading = -100.0
  • Player positions: P1 (490,448), P2 (480,576).
  • Weapon: 0x05 (Gauss Gun) for both.
  • Forces bonus_weapon_power_up_timer = 15.0.

Variant 2 — demo_setup_variant_2 (0x00402fe0)

  • player_count = 1
  • demo_time_limit_ms = 5000
  • Spawns template 0x41 in columns at y=128..788 step 60, with x offsets:
  • x = 32, 128, -64, 768 (alternating by row parity)
  • heading = -100.0
  • Weapon: 0x15 (Ion Minigun).

Variant 3 — demo_setup_variant_3 (0x00403250)

  • player_count = 1
  • terrain_generate(&quest_selected_meta) (uses the currently selected quest descriptor).
  • demo_time_limit_ms = 4000
  • Spawns random templates 0x24 and 0x25 at positions similar to variant 1.
  • Player position: (512,512).
  • Weapon: 0x12 (Pulse Gun).
  • Uses heading = 0.0 for spawns.

Variant 5 — purchase interstitial — demo_purchase_interstitial_begin (0x00403370)

  • demo_time_limit_ms = 10000
  • demo_purchase_screen_active = 1 (so the main loop skips gameplay and only renders the upsell overlay)

Rewrite note: Out of scope (storefront defunct). The rewrite omits this variant and the upsell overlay entirely.

Upsell overlay (demo_purchase_screen_update / 0x0040b740)

Rewrite note: Out of scope (storefront defunct). We only implement the demo loop; no purchase screen or "Buy Now" flow.

This runs whenever demo_mode_active != 0:

  • When demo_purchase_screen_active == 0
  • Shows a rotating “Want more …” message (demo_upsell_message_index).

  • On user input, activates the full purchase screen:

    • demo_purchase_screen_active = 1
    • demo_time_limit_ms = 16000

  • When demo_purchase_screen_active != 0

  • Renders the full-screen purchase UI (backplasma + mockup + logo, feature list).
  • Buttons:
    • Purchase: sets shareware_offer_seen_latch and opens the purchase URL (then requests quit).
    • Maybe later: starts a transition back to menu state 0 and resumes crimson_theme.
  • Increments quest_spawn_timeline itself and restarts the demo via demo_mode_start() once quest_spawn_timeline > demo_time_limit_ms.

Exiting demo mode (returning to menu)

When the upsell overlay triggers a transition to state 0, the UI transition manager (ui_elements_update_and_render @ 0x0041a530) does two demo-specific things:

  • If demo_mode_active and game_state_pending == 0, it calls terrain_generate_random() right before game_state_set(0) (so the menu background changes).
  • Once the menu transition finishes, it clears demo_mode_active and reloads presets (config_load_presets()).

Player behavior in demo mode (autoplay)

player_update @ 0x004136b0 treats demo_mode_active as a control-scheme override and routes through the same logic as the “auto-aim” control mode:

  • Maintains player_auto_target (player+0x2fc) as the nearest living creature with a 64-unit hysteresis.
  • Aiming is biased by arena center:
  • if no valid target: aim away from (512,512)
  • if within 300 units of center: aim at the target; otherwise aim relative to center

The exact firing behavior in this mode still needs confirmation (movement/aim are clearly autonomous; the fire gating should be verified with a runtime probe).