in a computer graphics rendering process , a first triangle - shaped primitive and a second triangle - shaped primitive that are connected are optionally combined to form a quadrangle - shaped primitive . when the first and second triangle - shaped primitives are combined , the resultant quadrangle - shaped primitive is forwarded to a quad - based rasterization process . otherwise , the first triangle - shaped primitive is forwarded to the rasterization process . the second triangle - shaped primitive may also be forwarded to the rasterization process separate from the first , or it may be used to form a quadrangle in combination with another triangle primitive connected to it . a graphics subsystem could effectively double its throughput of connected triangle primitives by going from three vertices and three edges per primitive to four vertices and four edges per primitive .