An engineer who analyzed the iPhone X's display paid attention first to the cutout and four round corners. The moment he saw the pixels located near the four round corners with a microscope, he said, "I would definitely not want to do this job." He was engaged in the development of displays at a major electronics manufacturer.
OLED panels emit light because electric current flows in the diodes of pixels. When electricity flowing in the diodes changes, so does the brightness of light emission. This is used for controlling gradation for displaying images. Electric current flowing in the diodes is controlled by using TFTs (thin-film transistors). This is the basic mechanism that drives OLED panels.
The brightness of pixel changes due to various factors such as (1) the length of gate lines that transmit signals, (2) position of gate driver circuit and (3) variation of TFT at the time of manufacturing. Therefore, TFT needs to be designed so that the brightness of each pixel becomes the same.
In the case of odd-shaped panels, the gate line length is different from those of conventional rectangular panels in some parts due to round corners, cutout, etc. Moreover, gate lines are probably extended alternately from the right and left (long) sides of the panel. In this case, the density of wiring near the cutout increases by 100% because gate lines can be arranged only from one side near the cutout.
"There is not enough space for a gate driver circuit to be formed at the edge of the panel, and parts that cannot be contained might be located on the upper short side of the panel," an engineer said.