Draw particles, match the client's fog, and measure frame delay

Particles (point sprites) are drawn as instanced camera-facing squares sized like Direct3D 9's. Fog is by depth buffer value, as Direct3D 9 does with IMVU's projections. At most one frame is queued for display, frames carry the adapter's timestamp so the renderer process logs the delay to presenting, and the log's lines from several processes no longer mix.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/interface.md

@@ -71,7 +71,12 @@ virtual methods, IMVU's code only uses an engine through helpers that call its v
   vertical field of view, Direct3D's 0 to 1 depth) and an orthographic one for 2D, orthonormal view rotations,
   opaque clear colors, ambient light with zero alpha, linear fog (1 to 50), scrolling texture transforms. Furniture
   vertices are interleaved: positions and normals are 12-byte elements 32 bytes apart, so strides matter.
-- Still unknown: point sprites (`drawPointSprites`, particles), render targets, `CompoundRegion` (texture update
+- Particles (`drawPointSprites`): a Visual C++ 2010 `std::vector` of 16-byte points (position, color), drawn as
+  Direct3D 9 point sprites: squares viewport height / distance pixels across (Direct3D 9's defaults clamp them to
+  1 to 64; IMVU sets only the size, 1, and the scale factors 0, 0, 1), textured over the whole square.
+- Fog: linear table fog. Direct3D 9 fogs by eye distance only for projections whose (3, 4) element is +1; IMVU's are
+  right-handed (-1), so it fogs by depth buffer value (0 to 1) against start 1 and end 50: in effect no fog.
+- Still unknown: render targets, `CompoundRegion` (texture update
   regions), `newRenderTexture`'s flags, and what `beginRendering` does with a null target. MSVC orders overloaded
   virtual methods unlike their declaration, so our declarations never overload virtual methods.
 - Memory crosses the boundary only through virtual methods (destructors, control blocks), so each side can use its