Environment rendering

The environment browser contains 240 recorded 320 × 200 frames produced by the original DBSIM renderer: ten views/layer combinations for each of the 24 supplied WLD descriptors. They are controlled background captures, without cockpit, terrain models, buildings or actors. tools/native_environment.py supplies the established resource/VGA harness, original Mode-X dispatch table, explicit camera and preference inputs. tools/capture_environment.py regenerates the frames and cloud sequence.

The original background entry 0x25b68 draws sky/ground and the horizon panorama, then clouds, then optional ground marks, then updates the view-dependent palette band. Ordinary scenery and actors follow in a separate pass.

Resource selection

0x251c4 selects WORLD(terrain*6 + time*2 + visibility).WLD and the even WORLD(terrain*6 + time*2).DPL palette. Terrain is desert, temperate, ice or urban; time is day, dusk or night; visibility is normal or low. These are selected mission conditions, not a continuous day/night cycle.

The WLD's five strings bind, in order:

Low-visibility descriptors omit the horizon panorama. All supplied descriptors request twenty clouds and 250 ground-mark slots. worlds.json preserves every field and the full resource names. The twelve opening signed words contain horizon-band width; sky palette start, step and count; ground palette start, step and count; horizon offset; ground-mark colour; a retained word at offset 18; and the two palette endpoints used by the view-dependent reflection band. The word at offset 18 is passed to 0x6cf8, which selects the secondary ground-effect model FLAT.DTS (zero) or FLAT2.DTS (nonzero); it is not part of the background palette-cycle pointer.

Sky and distant horizon

0x26264/0x2627f build the rolled horizon from camera pitch, roll and viewport settings. 0x2650b and 0x267d7 draw the palette bands. The lower-detail polygons already have independent full-frame checks in check_background_raster.py.

0x26ac5 scrolls the panorama's bitmap strip according to unsigned heading, wrapping across the DBA's frames. It uses plain bitmap drawing for zero roll and rotated bitmap drawing otherwise. The panorama overlays the background bands/ground texture; it is not terrain geometry placed at a finite distance. Preference byte 0xbd565 independently enables it.

Ground detail

The preference initializer 0x4afe8 establishes threshold 240 at 0x956be. Ground-detail byte 0xbd567 selects three cases:

• Below 240: gradient ground plus a fraction of the 250 generated marks. The active count is floor(250 * detail / 240).
• Exactly 240: gradient ground, without marks or the ground texture.
• Above 240: the projected TRENCHES.64K texture, when the sky object's texture-enable flag is set. Values 241–255 select the same texture path.

0x29120, 0x28fbc and assembly sampler 0x2991d perform the high-detail projection and palette translation. The 256 × 256 source uses indices F0–FF. Camera heading rotates its sampling axes; camera height and horizon position control perspective. World X/Y wrap to their low sixteen bits. Translating the camera by 65,536 units in both axes produces an identical cloud-disabled background in all 24 native captures.

The texture has its own fifteen distance-translation rows. 0x28de8 builds these from the WLD ground band; TEX/TEX_LO select the row by distance. This is separate from the model textures discussed in LIGHTING.md: those retain brightness with object distance, whereas this ground texture does receive its own distance treatment.

Ground marks (0x26edd, 0x26fdd) are generated with the secondary RNG around the initial camera, at Z=0. Points more than 70,000 units away after camera movement are reflected around the old/new camera midpoint to recycle the field. Within 30,000 units a mark gains a second pixel; within 20,000 it gains three more, with two darker palette entries. They are not authored map objects.

The banked full-screen inspection fixtures retain some pixels that the original background routine leaves untouched (counts are recorded per frame). The capture clears these to black, so their gaps remain visible. This establishes the isolated routine's coverage under this viewport; it does not establish that the same pixels are visible through the actual cockpit or in every game view.

Clouds and update clocks

The cloud object uses vtable 0x928f6; 0x27c00 initializes its random field and wind, and 0x27d78 advances/draws it. Cloud-detail byte 0xbd566 controls the active count: floor(20 * (detail + 1) / 256). Initialization still takes place when that count is zero, so disabling clouds does not remove all their initial secondary-RNG consumption.

Wind is chosen once using the secondary RNG. The native code chooses a speed from 50–149 and an angle, then produces the horizontal fixed-point components. Each draw adds that vector to the active clouds. It does not multiply by the simulation's Q8 frame ratio. Clouds recycle around a moving camera with hysteresis. Texture choice and visibility/distance behavior remain original methods, not browser particle approximations.

The retained animation records 120 calls, sampling every fourth. Its 100 ms GIF delay is chosen for inspection and is explicitly not a measured game rate. All gallery comparisons restore the initialized cloud/point field so that changing layers does not accidentally advance the wind. Capture seed 17 means 17 warm-up steps of the original secondary generator, not a recovered TAP seed.

Palette changes and optional cycles

0x25fe1 changes palette entries 64–79 with camera pitch when its gate is enabled. It interpolates sixteen endpoints between the WLD's two selected colours, chooses min(15, uint16(pitch + 8192) >> 10), and builds a ramp from the cached original colour 64 to that endpoint. The override at 0x928ee can supply one band directly, after which it resets to -1. Damage's impact mode uses colour 98 instead, alongside the separate impact palette swap.

The original fixed-point interpolation truncates signed Q8 component increments and shifts each accumulated component separately. check_environment_palette.py independently matches ten pitch inputs, the one-shot override and impact mode for all twelve supplied palettes. These are palette responses to view and damage, not a clock that changes the mission's time of day.

0x2e17c starts the player's impact flash for 60 UI-clock units; 0x2e1d7 toggles it at secondary-RNG intervals below ten and displaces the cockpit panel. View mode 4 suppresses it. The palette paths are also gated while the separate cockpit/view fade routines own the palette.

The renderer retains optional WORLD*.CYC support, but none of these files exists in the supplied volumes. Each six-byte record contains start index, colour count and period; 0x281cc registers at most five. 0x28260, called at frame presentation, acts only when next_due < clock, then schedules clock + period, discarding overshoot. It rotates from the current mutable palette by an increasing offset; its first event uses offset zero. A labelled synthetic four-colour record independently verifies that behavior and removal. No artificial cycles are added to the real world previews. The unused file loader advances its record pointer by twelve while allocating six bytes per record; this legacy inconsistency is retained in the notes, not exercised with invented multi-record game content.

Remaining composition work concerns moving actors, effects and full recorded mission replay. These environment captures do not claim that end-to-end loop.

Main-view cloud animation and complete horizon inspection

The world browser now animates the selected camera view directly, with pause and frame scrubbing. export_environment_browser.py records thirty frames for each of eight cloud-enabled views/layer settings in all 24 worlds: 5,760 frames. Each displayed frame represents four original cloud draws; the chosen 100 ms playback delay remains an inspection speed, not a measured game rate.

The exporter restores a cached native background, sets the original camera and calls native cloud entry 0x27d78. Unsampled calls execute the original movement and omit drawing only; the camera is stationary. First and last images of every sequence are compared pixel-for-pixel with the complete environment entry. The first also matches its existing capture. check_environment_browser.py verifies every saved atlas frame and checks the original stills and palettes.

The full 360° option unfolds the four 320-pixel horizon sections, over original level sky/ground bands, into a 1,280 × 200 strip. Original heading scroll moves the strip right as heading increases, so the contiguous stored order is captured at headings 0°, 270°, 180° and 90°. It is an inspection layout, not a perspective camera stretched across 360°. Clouds and perspective ground remain in the camera views; low-visibility worlds correctly show bands without a horizon bitmap.

The old quarter-turn choices were a small set of recorded viewpoints, not a limit imposed by the game. The earlier temperate-only cloud GIF remains an archived reference, but has been removed as a separate viewer panel.

Native horizon integration

The C++ flight view now draws the original panorama over the established sky/ ground bands and respects the shell's horizon-detail setting. Its placement retains unsigned-heading wrap, the original fixed 320-pixel strip walk, pitch/ roll offsets and separate level/rotated bitmap paths. Rotated quads use geometric width/height but source texture endpoints width-1/height-1; the original affine mapper handles their transparency and cockpit scan direction.

capture_panorama.py records 576 original full frames and every bitmap placement across all 24 worlds, varied heading/pitch/roll and rectangular viewports. capture_cockpit_panorama.py adds 96 complete frames through all 32 original cockpit windows/masks. Native C++ matches all pixels and recorded placements. The captures run original background and bitmap code with file/heap/VGA transport supplied; cloud, ground-mark and high-detail ground-texture layers are excluded from this fixture and covered by the combined environment comparisons below.

The original panorama loop assumes a positive horizontal stride. Inverted or exact quarter-turn roll can make its progression invalid; native placement reports that domain rather than looping indefinitely. These probes cover the ordinary positive-stride roll range, not that invalid original endpoint.

Native cloud and mark integration

The native implementation now preserves the original cloud and mark fields, not just their appearance. capture_ground_marks.py records 224 complete frames and every point/anchor/RNG state across four terrain families. capture_clouds.py records 144 full frames / 501 draws, with positions, hysteresis flags, wind, texture choice and complete RNG states. Native output matches every record, including both cloud faces, near clipping and original cockpit masks.

Clouds consume eight random ring offsets inherited from their base class, but the derived distance callback at 0x25a50 is empty. These offsets do not change their geometry. All twenty slots recycle with camera movement even when inactive; wind moves only the active subset. Marks differ: only active slots recycle, and detail >= 240 retains their previous anchor and active count. Both fields still initialize at zero detail, so their initial random draws must be preserved.

Ground projection context correction

The high-detail ground sampler reads the viewport's stored origin directly, whereas sky, horizon and clouds use the derived projection centre. Original 0x5bf68 establishes centre = bounds.top_left - origin. The earlier isolated environment harness supplied the derived centre but left that origin zero; this compressed the ground perspective in its high-detail previews. The harness now supplies the matching (-160,-100) origin for its full-screen camera, and all 24 complete horizons and 5,760 original cloud-animation frames have been regenerated and verified. Cockpit captures additionally derive the origin from each authored window. Geometry/model analysis is separate.

The new ground-texture comparison also preserves the original cached scanlines: height, pitch, row-count growth and horizontal scroll invalidate the cache; viewport, projection shift and shorter row counts do not. Its scratch-bitmap stride survives a return from banked to level view. These are renderer state, not an opportunity to replace the original with a generic perspective texture.

Complete native environment comparison

capture_environment_composition.py executes the entire original 0x25b68 environment draw with all layers and reflection updates enabled. Native output matches all 288 frames across 24 worlds, full visual RNG state and palette entries 64..79. Cameras, viewport masks, detail thresholds, panorama toggles and projection offsets vary sequentially. The isolated ground sampler additionally matches 480 full frames and scratch bitmaps. Reflection checks cover 144 original pitch, one-shot override and impact palettes. Impact timing, camera disturbance and the full simulator frame owner are integrated; see the impact checks below and RUNTIME.md.

Cockpit impact flash and displacement

Player torso/head damage that changes its condition band calls DBSIM 0x2e17c. This is a cockpit effect, not a general world-camera rotation: the outside projection stays fixed while the retained panel, clipping spans and widgets move vertically. Initial displacement stays within five pixels (upward on the forward and side views, downward on the lower panel). Forward/lower views expose adjacent artwork in the shared VGA surface; side views clear the exposed strip to index 63. Original frames for all four views are in analysis/cockpits/impact/index.html.

The effect owns a 60-unit UI-clock deadline. Repeated damage extends it without restarting the random sequence. Each active update chooses an unsigned 16-bit secondary-RNG value modulo five for motion. A strict clock > next-toggle test swaps palettes and draws a new modulo-ten interval. Expiry is cleared first; restoration happens on the next update. Mode 4 suppresses the effect. The authored IMPACT1.DPL is loaded unchanged; reflection entries 64–79 still use the separately cached base/impact endpoint, and shield indicator colours continue to update.

Original 0x243d4/0x24564/0x24750 move the two VGA page origins, subtract displacement from both rectangular and span-list scene clips, and translate the widget owner. View changes restore the old view (0x222c0), then resume with a ten-pixel range (0x242f6); external view cancels that resumption. Palette ownership and a pending view transition have separate gates.

capture_cockpit_impact.py records 5,005 original calls over 50 scenarios. The native owner agrees on both clocks, palette identities/flags, page origins, clip regions, widget translation and every secondary-RNG word, including repeated hits, view changes, suppressed effects, zero-clock sentinels and unsigned wrap. Graphical page save/copy and widget translation are explicit capture boundaries; original clip mutation executes unchanged. Separate initialized-original captures show complete images in each view. Whole-game frame scheduling is compared in the complete replays described in RUNTIME.md, alongside these controlled impact updates.

Cockpit layout offset at the environment call

Original 25b68 passes afa9c/afaa0 to 26264. These are the authored VUE instrument origins, independently of the already shifted world projection centre. Forward uses (0,0), side panels use (+320,0) and (-320,0), and lower views retain their authored vertical offset. The side-view camera capture in analysis/cockpits/view-camera.json records both fields. Supplying only the shifted projection centre leaves part of the side-panel sky unpainted; the native mission caller has been corrected to supply both original inputs.

World-selected ground-effect models

World descriptor word 18 selects FLAT.DTS when zero and FLAT2.DTS otherwise (original loader 6cf8). The mission effect owner now uses that selector for both HERC ground attachments and secondary explosion models. Previously it always loaded FLAT.DTS, leaving bright orange shadows in worlds that require FLAT2's palette index 224 instead of 240.

Three independent original DEMO2 regions cover the corrected shadow in the centre and at both viewport edges (frames 900, 960 and 1740). They match exactly; the largest complete sampled DEMO2 difference falls from 195 to 90 RGB pixels. These regions join the existing original replay scene fixtures.

Ground projection at lookup-table boundaries

Original 28fbc builds a negative-pitch rotation with 694b8 and transposes that same quantized matrix with 63df0 for the inverse. Recomputing a positive-pitch matrix instead changes the result at the cosine table's rounding ties. This caused 61 different scratch-texture pixels at the DEMO3 frame-1320 camera pose.

The native ground projector now transposes the existing coefficients. The independent capture_ground_replay_precision.py fixture checks 66 complete original ground frames and sampler bitmaps, covering that replay pose and neighbouring positive/negative rounding boundaries at several headings. All agree. The complete sampled frame now differs by only three RGB pixels; that count includes other scene elements and is not a whole-frame equality claim.