Community Property (Texas) Is it half of the Wages in Box 1 of his/her W-2s? Or is it half his/her Taxable Amount after the Deductions?

As I understand it, for Texas's Community Property Law the way the amount is figured is that you would calculate half of your spouse's income and place it in the Community Property Addition Adjustment field. Then calculate half of your own income and place it in the Community Property Subtraction Adjustment field. My question is: What number are we using? Is it half of the Wages in Box 1 of his/her W-2? Or is it half his/her Taxable Amount after the Deductions?