UNPACK_FLIP_Y_WEBGL=true was correct for screen orientation but the
shader's rotated-frame math expected it false. To get both right:
- Re-enable UNPACK_FLIP_Y_WEBGL=true so canvas top maps to texture
V=1 (screen top). Text now reads right-side up.
- Invert the drawing axes: canvasY = (-lng + halfLong + 0.5)*TILE_SIZE
so lng=+12 (corridor front, ahead) lands at small canvas Y, which
after upload ends up at texture V=1, i.e. at screen top.
Same inversion for perp.
- Shader's gUv.y = rotated.x / uGroundSize.y + 0.5 is unchanged:
for offset.z=+12 (north) it samples V=0.98 -> texture row 6271
-> canvas row 128 (the new top-of-corridor row) -> lng=+12. Correct.
Effect: N labels read upright, image orientation matches world
directions, and corridor scrolls in the visible flight direction.
Richard Zink
2fd394a865