In this paper, we present an efficient 3D rendering method capable of parallel processing for a glasses-free 3D display based on eye-tracking. The proposed 1WDSR (1-way directional subpixel rendering) method allocates subpixel values according to the average position of the viewer’s left and right eyes, and has high computational efficiency without deteriorating 3D image quality. Experimental results have shown that 3D rendering time is reduced to less than 50% compared to the directional subpixel rendering (DSR) method previously proposed by the author while maintaining 3D rendering accuracy.