Legal Question in Criminal Law in Texas

This is definitely not legal. The Penal Code limits the right to defend property by force as follows:

A person in lawful possession of land or tangible, movable property is justified in using force against another when and to the degree the actor reasonably believes the force is immediately necessary to prevent or terminate the other's trespass on the land or unlawful interference with the property. (TX Penal Code Sect. 9.41)

However, a gun constitutes deadly force, which is governed by Penal Code 9.42:

A person is justified in using deadly force against another to protect land or tangible, movable property: (1) if he would be justified in using force against the other under Section 9.41; and (2) when and to the degree he reasonably believes the deadly force is immediately necessary: (A) to prevent the other's imminent commission of arson, burglary, robbery, aggravated robbery, theft during the nighttime, or criminal mischief during the nighttime; or (B) to prevent the other who is fleeing immediately after committing burglary, robbery, aggravated robbery, or theft during the nighttime from escaping with the property; and (3) he reasonably believes that: (A) the land or property cannot be protected or recovered by any other means; or (B) the use of force other than deadly force to protect or recover the land or property would expose the actor or another to a substantial risk of death or serious bodily injury.

So there is no blanket permission to use deadly force or give a warning shot and then use deadly force if someone is simply trespassing on your property. Under your situation, you would have to "reasonably" believe that the person was imminently going to commit one of the above felonies and either reasonably believe that the property can't be protected by any other means or that use of non-deadly force to protect the property would expose you to substantial risk of death of serious bodily injury. If someone is on your property at night (and you have no other information), it's probably not permissible to shoot them.