ttransform.c - plan9port - [fork] Plan 9 from user space
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       ttransform.c (1995B)
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            1 /*
            2  * The following routines transform points and planes from one space
            3  * to another.  Points and planes are represented by their
            4  * homogeneous coordinates, stored in variables of type Point3.
            5  */
            6 #include <u.h>
            7 #include <libc.h>
            8 #include <draw.h>
            9 #include <geometry.h>
           10 /*
           11  * Transform point p.
           12  */
           13 Point3 xformpoint(Point3 p, Space *to, Space *from){
           14         Point3 q, r;
           15         register double *m;
           16         if(from){
           17                 m=&from->t[0][0];
           18                 q.x=*m++*p.x; q.x+=*m++*p.y; q.x+=*m++*p.z; q.x+=*m++*p.w;
           19                 q.y=*m++*p.x; q.y+=*m++*p.y; q.y+=*m++*p.z; q.y+=*m++*p.w;
           20                 q.z=*m++*p.x; q.z+=*m++*p.y; q.z+=*m++*p.z; q.z+=*m++*p.w;
           21                 q.w=*m++*p.x; q.w+=*m++*p.y; q.w+=*m++*p.z; q.w+=*m  *p.w;
           22         }
           23         else
           24                 q=p;
           25         if(to){
           26                 m=&to->tinv[0][0];
           27                 r.x=*m++*q.x; r.x+=*m++*q.y; r.x+=*m++*q.z; r.x+=*m++*q.w;
           28                 r.y=*m++*q.x; r.y+=*m++*q.y; r.y+=*m++*q.z; r.y+=*m++*q.w;
           29                 r.z=*m++*q.x; r.z+=*m++*q.y; r.z+=*m++*q.z; r.z+=*m++*q.w;
           30                 r.w=*m++*q.x; r.w+=*m++*q.y; r.w+=*m++*q.z; r.w+=*m  *q.w;
           31         }
           32         else
           33                 r=q;
           34         return r;
           35 }
           36 /*
           37  * Transform point p with perspective division.
           38  */
           39 Point3 xformpointd(Point3 p, Space *to, Space *from){
           40         p=xformpoint(p, to, from);
           41         if(p.w!=0){
           42                 p.x/=p.w;
           43                 p.y/=p.w;
           44                 p.z/=p.w;
           45                 p.w=1;
           46         }
           47         return p;
           48 }
           49 /*
           50  * Transform plane p -- same as xformpoint, except multiply on the
           51  * other side by the inverse matrix.
           52  */
           53 Point3 xformplane(Point3 p, Space *to, Space *from){
           54         Point3 q, r;
           55         register double *m;
           56         if(from){
           57                 m=&from->tinv[0][0];
           58                 q.x =*m++*p.x; q.y =*m++*p.x; q.z =*m++*p.x; q.w =*m++*p.x;
           59                 q.x+=*m++*p.y; q.y+=*m++*p.y; q.z+=*m++*p.y; q.w+=*m++*p.y;
           60                 q.x+=*m++*p.z; q.y+=*m++*p.z; q.z+=*m++*p.z; q.w+=*m++*p.z;
           61                 q.x+=*m++*p.w; q.y+=*m++*p.w; q.z+=*m++*p.w; q.w+=*m  *p.w;
           62         }
           63         else
           64                 q=p;
           65         if(to){
           66                 m=&to->t[0][0];
           67                 r.x =*m++*q.x; r.y =*m++*q.x; r.z =*m++*q.x; r.w =*m++*q.x;
           68                 r.x+=*m++*q.y; r.y+=*m++*q.y; r.z+=*m++*q.y; r.w+=*m++*q.y;
           69                 r.x+=*m++*q.z; r.y+=*m++*q.z; r.z+=*m++*q.z; r.w+=*m++*q.z;
           70                 r.x+=*m++*q.w; r.y+=*m++*q.w; r.z+=*m++*q.w; r.w+=*m  *q.w;
           71         }
           72         else
           73                 r=q;
           74         return r;
           75 }