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feat(camera): #78 deterministic Camera.zoom (Q16.16 render-time zoom)
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The #78 investigation rejected hardware f32/f64 for the coordinate types
(they would desync lockstep/replay/save) and identified camera zoom as the
one genuinely-missing render feature. Ship it: Camera.zoom(scale) scales the
whole view about the screen centre by a Q16.16 factor, threaded through the
same two framebuffer chokepoints (rt_put_px/rt_fill_rect) that carry the
camera offset, so it composes with Camera.set/follow/shake. Gated by an
internal rt_cam_zoomed flag so a game that never zooms renders byte-for-byte
identically (golden renders unchanged); Camera.zoom(1.0) turns it back off.
The world coordinate types stay integer px + Q16.16 velocity, so it's a pure
render-time transform and itself deterministic.

Example examples/library/camera_zoom.ludic (pixel-readback verified),
docs page, RFC updated (docs/RFC-POSITION-TYPES.md). Full suite 105/0,
fixpoint holds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Orkun ÇAKILKAYA 2026-09-02 06:55:37 +03:00
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bump: minor
type: feat
Deterministic camera zoom (#78) — `Camera.zoom(scale)` scales the whole view about the screen centre by a Q16.16 factor (`1.0` = none, `2.0` = 2x in, `0.5` = out). It rides on the same two framebuffer chokepoints (`rt_put_px` / `rt_fill_rect`) that already carry the camera offset, so it composes with `Camera.set`/`follow`/`shake`, and it is a *render-time* transform — the world coordinate types stay integer pixels + Q16.16 velocity, so lockstep, replay and `world_save` are untouched, and the zoom itself is deterministic. Gated by an internal `rt_cam_zoomed` flag so a game that never zooms renders byte-for-byte identically (golden renders unchanged); `Camera.zoom(1.0)` turns it back off. This is the concrete outcome of the #78 position-types investigation (`docs/RFC-POSITION-TYPES.md`), which rejected hardware floats for the deterministic coordinate core and identified zoom as the one genuinely-missing render feature. Example: `examples/library/camera_zoom.ludic` (pixel-readback verified).