# mapview

A dev tool: every track drawn the way the pod's map screen draws it, with pan
and zoom, so you can ask "what does the map actually show here?" without booting
the game. Nothing here ships — [pack-dist.ps1](../../pack-dist.ps1) does not
look at it.

```powershell
python tools\mapview\build_mapview.py <rpl4tool-listing.txt> tools\mapview\mapview.html
```

Then open `mapview.html`. It is self-contained: track data, palette and all.

| key | |
|---|---|
| <kbd>&uarr;</kbd> <kbd>&darr;</kbd> <kbd>&larr;</kbd> <kbd>&rarr;</kbd> | pan north / south / west / east |
| <kbd>+</kbd> <kbd>-</kbd> | zoom in / out |
| <kbd>[</kbd> <kbd>]</kbd> | previous / next track |
| <kbd>F</kbd> / <kbd>A</kbd> | fit the course / fit everything |
| <kbd>G</kbd> | GPS or NavDisplay LOD behaviour |

Dragging pans and the wheel zooms.

## What it reproduces

`NavDisplay::CalculateBounds` ([RPL4GAUG.cpp:1587](../../RP_L4/RPL4GAUG.cpp#L1587))
derives `metersPerPixel` from the zoom and sets `LODIndex` to it. `L4GaugeImage::Draw`
([L4GAUIMA.cpp:908](../../MUNGA_L4/L4GAUIMA.cpp#L908)) then walks the LOD scales:

```c
for (lod_index = 0; lod_index < LODCount; ++lod_index)
    if (LOD_value <= LODScales[lod_index]) break;
if (lod_index < LODCount) { ...Draw... }        // else nothing is drawn
```

Scales ascend, so index 0 is the finest and running past the largest drops the
object entirely rather than simplifying it. The viewer does the same and reports
the count, though this content barely exercises it: every placement in every
track is `cn3`, which carries a single LOD at scale 1000, so nothing is dropped
until 1000 m/px and then all of it goes at once.

Two display modes, because the game has two map gauges and they disagree:

* **NavDisplay** &mdash; `nav(A,ModeAlwaysActive,(448,416),0x00,0x3C,...)`. The
  448&times;416 radar screen, LOD following the zoom.
* **GPS** &mdash; `gps(R,ModeAlwaysActive,(125,203),1.0)`. The 125&times;203 panel,
  LOD pinned at 1.0 by the config however far out it is scaled.

## Colour

Not a phosphor screen. Primitives carry palette indices and the palette is
whichever the port was configured with; for the pod's secondary port, where the
nav display lives, `L4GAUGE.CFG` says
`configure(0, sec, 270, 0x00ff, clut0, rgb, secpal.pcc)`. PCC is PCX, so the last
769 bytes are `0x0C` and 256 RGB triples. The walls come out grey because index
51 is `#4b4b4b`; the background is index 0, black. A primitive whose own colour
is 0 keeps the colour already set, which is the display's `staticColor`, `0x3C`.

Palettes are per-file, not global &mdash; 39 of 40 gauge PCCs differ from each
other &mdash; so the port's configured palette is the one that matters, not any
convenient nearby image.

## Orientation

Seen from above with +Z up the page, the engine's +X runs to the **left**. The
console's own picture of Brewer's Bane is what settles it: long leg up the right
side to Score Zone 1, the corner, then the run out to Score Zone 2. Drawn the
other way round every plan comes out mirrored, which is the bug this shares a
fix with in [../pages/](../pages/).