Iso 2.0 [2/12]: Positive-Z Nano Billboard Rendering (fence, gate, tall-grass)

[putersdcat]

Spec reference

IsoRenderingPlanV2.1.md §3.2 Positive-Z Nano; §Addendum A — Z-Pinned Shear

Goal

Positive-Z nano tiles render as Z-pinned upright billboards aligned to the left
iso axis. The bottom edge follows the iso angle (0.5 shear), vertical edges stay
vertical. Coverage: fence, gate, troll-bridge, tall-grass.

Technical requirements

Transform: ctx.translate(screenX, screenY+HALF_H); ctx.transform(1, 0.5, 0, 1, 0, 0);
Drawing: ctx.drawImage(img, 0, -drawH, 128, drawH);
drawH = zOffset × NANO_Z_SCALE (min 16px).

Acceptance criteria (ALL required to close)

• render_nano_tile fence straight-h → horizontal fence correct posts+rails, upright, no distortion.
• render_nano_tile fence corner-tl → L-corner variant correct.
• render_nano_tile gate straight-h → gate graphic visible, correct z-height.
• render_nano_tile tall-grass → semi-transparent flat grass decal.
• All 16 variants of fence rendered as a strip PNG (render_nano_scene 4×4 grid of variants).
• PNGs committed: ProgressEvaluations/nano-fence-all-variants.png, nano-gate-h.png, nano-tall-grass.png.

Verification command

render_nano_tile kind=fence variant=straight-h outputPath=ProgressEvaluations/nano-fence-h.png
render_nano_tile kind=fence variant=corner-tl outputPath=ProgressEvaluations/nano-fence-corner-tl.png