formats: decode the HUD glyph quad behind the objective counter

Following the pointers that move with REMAINING OB lands on four identical
objects whose first word is 0x820B2A64. Read live: that address holds 32
consecutive code pointers in 0x823c43b0..0x823c45a0 terminated by 0xfffffffc - a
vtable - and sylpheed.db has three ref xrefs to it from sub_823C3060,
sub_823C3148 and sub_823C31E0, i.e. three construction sites, the same pattern
the splash item vtable shows. No name: the disc's RTTI carries none.

The instance is a textured quad: a pixel size at +0x1c/+0x20 (34 x 42 for a
digit) and four vertices at +0x30/+0x48/+0x60/+0x78, each a colour and a UV pair.
The four UVs measured are the corners of an axis-aligned rectangle in order, all
0xffffffff.

The atlas size is a check rather than a guess: the UV rectangle is 0.0265 x
0.0547, and multiplying by 1280 x 768 gives 33.9 x 42.0 against the 34.0 x 42.0
stored in the object's own size fields - two independent fields agreeing to a
rounding step.

Also recorded: these objects churn. Re-reading an old pointer target a minute
later returned unrelated data, so this is a snapshot of a live pool.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMRJjbxLqZtsb5Vb7KunPE

docs/re/structures/hud-glyph-quad.md

@@ -0,0 +1,75 @@
+# The HUD's glyph quad — vtable `0x820B2A64`
+
+**Status: ✅ `CONFIRMED` for the object layout and the atlas size**, read live off
+a Stage 02 run and checked against itself. 🟡 the class has no name (RTTI carries
+none disc-wide).
+
+## How it was reached
+
+[`mission-objective-counter.md`](mission-objective-counter.md) found that the
+words moving with `REMAINING OB` are four ASCII digits and four guest pointers.
+Following the pointers lands on four objects with an identical shape, whose first
+word is `0x820B2A64`.
+
+## It is a vtable, with three constructors
+
+Read out of guest memory: **32 consecutive code pointers**, all inside
+`0x823c43b0 … 0x823c45a0`, terminated by `0xfffffffc`. `sylpheed.db` has three
+`ref` xrefs to it, from `sub_823C3060`, `sub_823C3148` and `sub_823C31E0` — three
+construction sites, the same pattern the splash item vtable `0x820b30b4` shows.
+The DB does not classify `0x820B2A64` itself as a vtable and knows no name for
+it, which is expected: the disc's RTTI carries no class names.
+
+## The instance
+
+```
+ -0x0c  f32   1280.0        ) the design space, immediately before the object
+ -0x08  f32    720.0        )
+ +0x00  u32   0x820B2A64    vtable
+ +0x1c  f32     34.0        width  in pixels
+ +0x20  f32     42.0        height in pixels
+ +0x30  u32   0xffffffff    vertex 0 colour
+ +0x34  f32   u                     u
+ +0x38  f32   v                     v
+ +0x48 … vertex 1   (+0x18 stride)
+ +0x60 … vertex 2
+ +0x78 … vertex 3
+```
+
+Measured on one digit glyph:
+
+| vertex | colour | u | v |
+|---|---|---|---|
+| 0 | `0xffffffff` | 0.5477 | 0.5013 |
+| 1 | `0xffffffff` | 0.5742 | 0.5013 |
+| 2 | `0xffffffff` | 0.5742 | 0.5560 |
+| 3 | `0xffffffff` | 0.5477 | 0.5560 |
+
+Four corners of an axis-aligned rectangle, in order, all untinted — a textured
+quad.
+
+## ✅ The atlas is 1280 × 768, and that is a check rather than a guess
+
+The UV rectangle is 0.0265 × 0.0547. Multiply by **1280 × 768**:
+
+```
+0.0265 × 1280 = 33.9   ->  the width  stored at +0x1c is 34.0
+0.0547 ×  768 = 42.0   ->  the height stored at +0x20 is 42.0
+```
+
+Two independent fields of the same object agree to within a rounding step, which
+is what makes the atlas size a measurement instead of a plausible number.
+
+## ⚠️ These objects churn
+
+The four pointers next to the counter swap as the digit changes, and re-reading
+one of the *old* targets a minute later returned unrelated data — the object had
+been recycled. Anything read here is a snapshot of a live pool, not a stable
+address.
+
+## What this is for
+
+It gives the port a decoded HUD text primitive: a glyph is a quad with a pixel
+size and four UVs into a 1280×768 atlas, drawn by a class with 32 virtual methods
+and three constructors. And it explains why the objective counter was so easy to
+find in RAM — the value sits inside the widget that renders it.