// SCV.DFS -- Scan Converter Definitions // // Copyright Xerox Corporation 1979 //Conditional compilation to decide how to handle splines. // Set SplineHandling to one of the three: manifest [ NoSplines=0 //Do not include spline code AdditiveSplines=1 //"Section and interpolate" spline code RecursiveSplines=2 //"Recursive" spline code SplineHandling=AdditiveSplines //You set this! ] // Define values of "guard" numbers // (a temporary measure -- the "gr" and "ls" compares // in QuickSort and Putsegment (sdirmin,sdirmax // compares, and also the "for s=l to r" loop) // will not work correctly for +inf=#77777 and -inf=#100000) // Following gives a range of -16000 < x < 16000 manifest [ plusinfinity=#37777 minusinfinity=#140000 ] // Structure for talking about scan-converting an object: structure SCV: [ Smin word //Bounding box of object Smax word Rmin word Rmax word //" Object word //Object descriptor Error word //Error (currently, just no more core) Sbegin word //S value to begin scan-conversion. Send word // and end. IntPtr word //Pointer to first intersection. IntCnt word //Count of intersections. ] // Following are included so privileged souls can read things from // the internal data structure, or use accumulators with confidence. structure HD: [ next word //pointer to next in list type word //type of thing (LINEtype or SPLINEtype) smin word //low value of s for this part smax word //high value of s for this part ] structure LINE: [ //block for a line descriptor @HD x word 2 //current x dx word 2 //delta ] structure SPLINE: [ //block for a spline @HD t0 word 2 dt word 2 coeffs word 8*2 ] structure RSPLINE: [ //Recursive spline evaluation @HD str word 2 //Order is important (initial stack order) gstr word 2 stl word 2 gstl word 2 rtr word 2 //R direction, F(tr) grtr word 2 // correction @ tr rtl word 2 // F(tl) grtl word 2 // correction @ tl ] //Floating-point AC's dedicated manifest [ t1=8 t2=9 t3=10 t4=11 //*** Order of following definitions is important *** //Coefficients for the spline (also range of T) esd=12 // D (scan direction) erd=13 // (run direction) esc=14 // C (coeff t) erc=15 esb=16 // B (coeff t^2) erb=17 esa=18 // A (coeff t^3) era=19 tminac=20 //Min value of parameter T tmaxac=21 // and max value //Current, old points csac=22 //Current point, scan direction crac=23 // " run direction osac=24 //Old point, scan direction orac=25 // " run direction //*** End of order-important stuff *** //Ac's for holding the "first" point from a MoveTo fsac=26 frac=27 //Matrix coefficients (second char is row, third is column) // (defined in order of SCVMatrix arguments) sssac=28 ssrac=29 srsac=30 srrac=31 //Ac's during scan-conversion. // esd to era are same // t1-t4 are used. tt1=csac tt2=crac tt3=osac // "Types" for object blocks (HD) LINEtype=0 SPLINEtype=1 ]