Field rendering and collision runtime

Field rendering and collision runtime

How the engine turns the field files into the running scene each frame: background tiles, depth, walkmesh movement, triggers and effects. The file formats themselves (.mim/.map/.id/.ca/.inf/.pmd) are documented in the Field File Format section; this page is the runtime view. Addresses for FF8_EN.exe, image base 0x400000.

Background rendering

Texture caching — the .mim is blitted into the emulated 1024×512 PSX VRAM: palettes at (0,232), tile pixels as 16 strips of 832×16 from y=256. The generic psxvram layer converts texture pages to DirectX surfaces on demand.
Tile list — Field_BG_BuildTileDrawList re-walks the raw .map records (16 bytes/tile) every frame, emitting a 16-byte sprite primitive per visible tile (with DR_TPAGE prims on texture-page changes) into double-buffered prim buffers.
Scroll and parallax — per-layer screen position = tile.xy + camera pan × parallax/256 + script scroll; .inf byte 15 is the parallax-enable mask and .inf+22 holds per-layer wrap sizes (layers wrap when scrolled out of bounds). The whole-screen pan is applied as display-environment offsets (Field_BG_UpdateScreenScroll, includes shake).
State/animation tiles (doors, lights) — tile byte 14 = state group, byte 15 = state value; a tile draws only when its value matches the group’s current state in the 4-byte/group state table ({R,G,B,state}). The RGB part is tweened by controller structs (current/target color + timer) — this is BGANIME/light-flicker. Door triggers flip the states through script entity flags.
Depth — one Z ordering table per frame (0..4095, inside the double-buffered render context): tiles insert at their .map Z, character polygons and shadows insert at GTE-projected Z — so per-tile occlusion of characters costs nothing.
FMV fields — .inf byte 14 = 1 makes Field_BG_CaptureVramForMovieMask snapshot the background and the .msk file keeps foreground tiles above the movie.

Walkmesh and movement

Triangles are 24 bytes (3 × int16 xyz verts) with a 3×int16 adjacency table and a script-lockable per-triangle blocked bitfield. Entities (612-byte structs) carry fixed-point position, current triangle, collision radius, speed scale and facing.

Movement step (Field_Walkmesh_MoveEntityStep): probes facing ±32 and straight rays with slope-attenuated speed; each ray also runs the entity-vs-entity cylinder test; the entity auto-rotates ±8 toward the free ray — that’s the wall slide.
Triangle transitions (Field_Walkmesh_ResolveMovement): 2D cross-product edge tests; leaving an edge hops to the adjacency neighbor unless it is −1 or blocked (wall + slide hint). Height always comes from the triangle plane equation — smooth slopes and stairs.
Entity collision (Field_Collision_EntityVsEntities): cylinder test on summed radii with height difference < 128; sets the touched flag consumed by TOUCH script events; through/push flags respected.

Triggers

Gateways (field exits, .inf+100, 12×32 B): line P1/P2, destination X/Y, destination walkmesh triangle, destination field id (< 0x48 = world map) and facing. A gateway fires when the player is within touch radius and the cross-product sign against the line flips between the old and new position. Spawn placement on the destination field uses the stored triangle (Field_Walkmesh_PlaceEntitiesOnLoad).
LINE triggers (script LINE/LINEON): lines live in the script-entity structs; Field_Collision_UpdateLineTriggerFlags latches WITHIN/LEAVE/CROSS/TOUCH/TALK/PUSH event flags that the script dispatcher consumes. Talk/push additionally require facing within 64/256 angle units and a button edge while stationary.
Door triggers (.inf+484, 12×16 B, modes 0–5): raise open/close request flags on the target script entity (Field_Collision_FireDoorTrigger) — sliding doors and background state flips.

Characters, shadows, effects

The .ca camera is parsed per frame; characters are posed (with head-tracking clamped to per-entity max angles) and rendered into the shared ordering table at projected Z. Circle shadows are 8 projected octagon segments with per-vertex radius/darkness. The PMD particle layer runs 16 emitters (254 B each) spawning into 128 particle slots of 32 bytes, camera-transformed as sprites (the Field_FX_* function family); save/draw-point pulses are 8 dedicated slots gated by the SetSavePoint state.

Function addresses

Function	Address	Description
`Field_MainLoop_UpdateFrame`	0x4767B0	Per-frame field update
`Field_BG_BuildTileDrawList`	0x475480	Rebuilds the background tile draw list from `.map`
`Field_BG_UpdateScreenScroll`	0x476450	Applies pan/scroll/shake display offsets
`Field_BG_UpdateScreenFade`	0x47B980	Screen fade update
`Field_BG_CaptureVramForMovieMask`	0x472A60	Snapshots background for FMV masking
`Field_Chara_UpdateEntitiesMotion`	0x4789A0	Updates character entity motion
`Field_Chara_SetModelPoseAndHeadLook`	0x472B30	Poses models and applies head-tracking
`Field_Chara_DrawCircleShadows`	0x472F20	Draws octagon circle shadows
`Field_FX_UpdateParticleEmitters`	0x473DE0	Updates the PMD particle emitters
`Field_FX_EmitterStepAndSpawn`	0x473C50	Steps and spawns particles for an emitter
`Field_FX_InitParticleSystem`	0x4743D0	Initializes the particle system
`Field_Walkmesh_MoveEntityStep`	0x479C60	Movement step and wall-slide probing
`Field_Walkmesh_ResolveMovement`	0x47A3E0	Triangle-to-triangle transition resolution
`Field_Walkmesh_HeightOnTriangle`	0x47A680	Height from the walkmesh triangle plane
`Field_Walkmesh_PlaceEntitiesOnLoad`	0x477C90	Spawns entities on their destination triangle
`Field_Collision_EntityVsEntities`	0x47A720	Entity-vs-entity cylinder collision test
`Field_Collision_UpdateLineTriggerFlags`	0x4775C0	Latches LINE trigger event flags
`Field_Collision_CheckGatewayCrossing`	0x477980	Gateway line-crossing test
`Field_Collision_CheckInfDoorTriggers`	0x47B610	Door trigger check from `.inf`
`Field_Collision_CheckTalkPushButton`	0x4777F0	Talk/push button-edge check
PSX VRAM buffer	0x1B46618	Global variable/data, not a function — emulated 1024×512 PSX VRAM
BGANIME state table	0x1A77238	Global variable/data, not a function — per-group tile state/color table

Addresses are for FF8_EN.exe (2000 PC release) as mapped in IDA (image base 0x400000).