Thank you! the game world is blacked by a canvas item shader on a colorrect overlay. the sonar circle radius increases at a 100 units per second, and has pixel alpha set to 0, revealing the terrain under it. and a green outline ring at the circle edge using smoothstep on the distance to radius delta. on release, 3 second lerp from 0 to 1 on the alpha, darkening the revealed area. similar fadeaway on the ring.
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I took a similar wrong turn on the initial world gen lol. Had to rewrite it too. The kraken pathing is still terrible lol. But it works for a jam game... prevent becoming too challenging because I don't have time for difficulty balancing.
The reason the shader ended up like that is that for the first 80% of dev there was no hiding at all, all islands and the 3 characters were fully visible so I could debug issues. So the overlay idea came from that.