drawImage(img, canvasX + TILE, canvasY + TILE, -TILE, -TILE)
flips the image both horizontally and vertically, so:
- Image north (high lat) ends up at canvas bottom (was top)
- Image south (low lat) ends up at canvas top
- Image east (high lon) ends up at canvas right
- Image west (low lon) ends up at canvas left
Combined with NO canvasY swap and the WebGL flip:
- North tiles drawn at canvas bottom -> after WebGL flip, still
at screen bottom. Screen bottom has image north = high y. So
y at screen bottom = high.
- Looking forward (close ground = screen bottom in cockpit) =
high y. y increases in flight direction.
With NO canvasX swap:
- East tiles (high x) drawn at canvas left
- Image east at canvas right within each tile (high x)
- Image west at canvas left within each tile (low x)
So at screen left: east tiles with image x increasing left to
right (low to high within tile). At screen right: west tiles with
image x decreasing left to right. Overall: x at screen right (west
tiles, low x label) lower than at screen left (east tiles, high x
label). x decreases left to right.
Richard Zink
23327a1cba