allowing a bot to detect other bots/walls/objects in its field of vision

Question

hi. i have a bot that is moving around between obstacles and other bots. has anyone got an algorithm or ideas on how to do this. the walls and objects are just red rectangles. the bots are just moving yellow circles. i cant do something to detect difference in color, as this requires objects to be touching, but i want my bot to avoid objects before it gets near them