# Drawing a Full Screen Quad

#### Posted on February 12th, 2015

Say you want to draw a full screen quad in clip space. The straight forward way to do it is to draw two triangles to cover the viewport. But why waste two triangles when you can do the very same thing with just one?

Drawing a triangle with vertices a, b and c covers the entire screen. To interpolate a parameter across the quad so that it has values u_{0},v_{0} and u_{1},v_{1} at the opposite corners of the quad, set the parameter values on the three vertices as in the diagram above and in the table below.

Position | Parameter | |||
---|---|---|---|---|

x | y | u | v | |

a | -1 | 1 | u_{0} |
v_{0} |

b | -1 | -3 | u_{0} |
2v_{1}-v_{0} |

c | 3 | 1 | 2u_{1}-u_{0} |
v_{0} |