void  SetViewParameters(float x1,float y1,float x2,float y2,float z1,float z2)

                Set the screen viewport parameters.

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                x1,y1,x2,y2: set the viewport on render screen, narmally it is the 0,0,max_x,max_y. if the x1 is -1, so it will not modify the viewport.

z1,z2:  [0-1] set the min, and max z depth on ths viewport