Near the bottom of the screen during a game of Vertex, you should be able to see a small icon with a circular arrow. This button can be pressed to undo the previous action you did on the puzzle ...

The vertex shader is used to transform the attributes of vertices (points of a triangle) such as color, texture, position and direction from the original color space to the display space.

Converts each vertex into a 2D screen position, and lighting may be applied to determine its color. A programmable vertex shader enables the application to perform custom transformations for ...