Optimize hot paths: distance calculations, collision detection, rendering

[Copilot]

Targeted micro-optimizations in frame-critical paths to reduce CPU overhead.

Changes

Distance calculations (game_state.zig)

• Defer sqrt until final result (compare squared distances)
• 3 sqrt ops → 1 per command

Collision detection (collision.zig)

• Cache grid lookup in resolveMove
• 2 worldToGrid calls → 1 per movement

Render batching (terrain_renderer.zig)

• Hoist constants outside 64×64 loop
• Pre-compute block_y_offset, grass_type_id

Function inlining

• Mark hot path helpers as inline: worldPos, cellTopY, worldToGrid, decoHeight, noise utilities
• Eliminates call overhead in tight loops

Main loop (main.zig)

• Skip clamp/lerp when position delta < threshold

Example

Before:

for (0..world.creature_count) |i| {
    const dist = @sqrt(dx*dx + dy*dy + dz*dz);  // 3 expensive sqrt ops
    min_dist = @min(min_dist, dist);
}

After:

for (0..world.creature_count) |i| {
    const dist_sq = dx*dx + dy*dy + dz*dz;  // cheap comparison
    min_dist_sq = @min(min_dist_sq, dist_sq);
}
return @sqrt(min_dist_sq);  // 1 sqrt at end

Impact

Estimated 5-15% reduction in game logic CPU usage. Most gains in movement/collision paths and 60 FPS render loop.

Original prompt

Improve performance

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