well those two have its own use . . so there is no equivalant to two . . but if you are working with compositing softwares you can use opengl to gain extra performance from your graphics card . also 3d applications use opengl for view port rendering . that way you can bring full use of your card. but as such opengl dont support many features as like dx. . . if you are interested in opengl programming . i suggest a google search . .
am just a compositor cum light specialist not a programmer

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