graphics.h: clarify docs about stride for YV12

This change makes it clearer how to derive the stride of the Cr and Cb plane
from the stride of the Y plane for the YV12 pixel format.

Change-Id: I54a9a20f35224bd583e25c615014cc8d830a1dd0

parent ce182cb8

include/system/graphics.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -78,7 +78,8 @@ enum {
		* - a vertical stride equal to the height
		*
		* y_size = stride * height
		* c_size = ALIGN(stride/2, 16) * height/2
		* c_stride = ALIGN(stride/2, 16)
		* c_size = c_stride * height/2
		* size = y_size + c_size * 2
		* cr_offset = y_size
		* cb_offset = y_size + c_size