//All start position is from the player's eyes
@JvmStatic
fun getCenterDistance(blockPos: BlockPos) = mc.thePlayer.getPositionEyes(mc.getRenderPartialTicks()).distanceTo(blockPos.vec)

//from LB ChestAura.(simplified)
@JvmStatic
fun canBlockBeSeen(blockPos: BlockPos) = mc.theWorld.rayTraceBlocks(mc.thePlayer.getPositionEyes(mc.renderPartialTicks), blockPos.vec, false, false, false)?.blockPos == blockPos

//getAllInBox -> Iterable<BlockPos>
@JvmStatic
fun searchBlocks(radius: Int): Map<BlockPos, Block> = BlockPos.getAllInBox(BlockPos(mc.thePlayer.getPositionEyes(mc.renderPartialTicks).addVector(-radius.toDouble(), -radius.toDouble(), -radius.toDouble())), BlockPos(mc.thePlayer.getPositionEyes(mc.renderPartialTicks).addVector(radius.toDouble(), radius.toDouble(), radius.toDouble()))).map { it to getBlock(it) }.toMap()

My BlockPos.getVec():

/**
     * Get the center position of this BlockPos
     */
    public Vec3 getVec() {
    	final AxisAlignedBB axisAlignedBB = Minecraft.theWorld.getBlockState(this).getBoundingBox(Minecraft.theWorld, this);
    	return new Vec3(getX() + 0.5 * (axisAlignedBB.maxX + axisAlignedBB.minX), getY() + 0.5 * (axisAlignedBB.maxY + axisAlignedBB.minY), getZ() + 0.5 * (axisAlignedBB.maxZ + axisAlignedBB.minZ));
    }

PS: I have seen BlockPos.getVec() in LB's ChestAura, but it doesn't exist in ScriptAPI and MCP. (and I want to ask why u used getter in .kt class?
BlockESP should use searchBlocks too.