package pass

import (
	"sort"
	"zworld/engine/object/mesh"
	"zworld/engine/render/uniform"
	"zworld/plugins/math/vec3"
)

func DepthSortGroups(cache MaterialCache, frame int, cam uniform.Camera, meshes []mesh.Mesh) DrawGroups {
	eye := cam.Eye.XYZ()

	// perform back-to-front depth sorting
	// we use the closest point on the meshes bounding sphere as a heuristic
	sort.SliceStable(meshes, func(i, j int) bool {
		// return true if meshes[i] is further away than meshes[j]
		first, second := meshes[i].BoundingSphere(), meshes[j].BoundingSphere()

		di := vec3.Distance(eye, first.Center) - first.Radius
		dj := vec3.Distance(eye, second.Center) - second.Radius
		return di > dj
	})

	// sort meshes by material
	return OrderedGroups(cache, frame, meshes)
}