Cull a bounding box (-1, 1) using the MVP transform.

cull.c

// Check if a tile is visible onscreen using it's MVP transform.
static inline bool MapTileFrustumCull(const mat4 mvp){
	// Clip space center and extents.
	vec4 c = {mvp.m[12], mvp.m[13], mvp.m[14], mvp.m[15]};
	vfloat ex = vabs(mvp.m[ 0]) + vabs(mvp.m[ 4]) + vabs(mvp.m[ 8]);
	vfloat ey = vabs(mvp.m[ 1]) + vabs(mvp.m[ 5]) + vabs(mvp.m[ 9]);
	vfloat ez = vabs(mvp.m[ 2]) + vabs(mvp.m[ 6]) + vabs(mvp.m[10]);
	
	// Check the bounds against the clip space viewport using a conservative w-value.
	vfloat w = vmax(0, c.w + vabs(mvp.m[ 3]) + vabs(mvp.m[ 7]) + vabs(mvp.m[11]));
	return ((vabs(c.x) - ex < w) && (vabs(c.y) - ey < w) && (vabs(c.z) - ez < w));
}