# Cohen-Sutherland Algorithm for line clipping

``` procedure CohenSutherlandLineClipAndDraw( x0,y0,x1,y1,xmin,xmax,ymin,ymax : real ; value: integer); { Cohen-Sutherland clipping algorithm for line P0=(x1,y0) to P1=(x1,y1) and clip rectangle with diagonal from (xmin,ymin) to (xmax,ymax).} type edge = (LEFT,RIGHT,BOTTOM,TOP); outcode = set of edge; var accept,done : boolean; outcode0,outcode1,outcodeOut : outcode; {Outcodes for P0,P1, and whichever point lies outside the clip rectangle} x,y : real; procedure CompOutCode(x,y: real; var code:outcode); {Compute outcode for the point (x,y) } begin code := []; if y > ymax then code := [TOP] else if y < ymin then code := [BOTTOM]; if x > xmax then code := code +[RIGHT] else if x < xmin then code := code +[LEFT] end; begin accept := false; done := false; CompOutCode (x0,y0,outcode0); CompOutCode (x1,y1,outcode1); repeat if(outcode0=[]) and (outcode1=[]) then {Trivial accept and exit} begin accept := true; done:=true end else if (outcode0*outcode1) <> [] then done := true {Logical intersection is true, so trivial reject and exi t.} else {Failed both tests, so calculate the line segment to clip; from an outside point to an intersection with clip edge.} begin {At least one endpoint is outside the clip rectangle; pick it.} if outcode0 <> [] then outcodeOut := outcode0 else outcodeOut := outcode1; {Now find intersection point; use formulas y=y0+slope*(x-x0),x=x0+(1/slope)*(y-y0).} if TOP in outcodeOut then begin {Divide line at top of clip rectangle} x := x0 + (x1 - x0) * (ymax - y0) / (y1 - y0); y := ymax end if BOTTOM in outcodeOut then begin {Divide line at bottom of clip rectangle} x := x0 + (x1 - x0) * (ymin - y0) / (y1 - y0); y := ymax end else if RIGHT in outcodeOut then begin {Divide line at right edge of clip rectangle} y := y0 + (y1 - y0) * (xmax - x0) / (x1 - x0); x := xmax end else if LEFT in outcodeOut then begin {Divide line at left edge of clip rectangle} y := y0 + (y1 - y0) * (xmin - x0) / (x1 - x0); x := xmin end; {Now we move outside point to intersection point to clip, and get ready for next pass.} if (outcodeOut = outcode0) then begin x0 := x; y0 := y; CompOutCode(x0,y0,outcode0) end else begin x1 := x; y1 := y; CompOutCode(x1,y1,outcode1); end end {subdivide} until done; if accept then MidpointLineReal(x0,y0,x1,y1,value) {Version for real coordin ates} end; {CohenSutherlandLineClipAndDraw} ```

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Contact:
Haowei Hsieh
hhsieh@cc.gatech.edu
http://www.cc.gatech.edu/gvu/people/Masters/Haowei.Hsieh.html
Last Change : Feb 19,1995