2: /*
  3:     Code for drawing color interpolated triangles using X-windows.
  4: */
  5: #include <../src/sys/classes/draw/impls/x/ximpl.h>

  7: #define SHIFT_VAL 6

 11: PetscErrorCode PetscDrawInterpolatedTriangle_X(PetscDraw_X *win,int x1,int y_1,int t1,int x2,int y2,int t2,int x3,int y3,int t3)
 12: {
 13:   PetscReal rfrac,lfrac;
 14:   PetscReal R_y2_y_1,R_y3_y_1,R_y3_y2;
 15:   int       lc,rc = 0,lx,rx = 0,xx,y,c;
 16:   int       rc_lc,rx_lx,t2_t1,x2_x1,t3_t1,x3_x1,t3_t2,x3_x2;

 19:   /*
 20:         Is triangle even visible in window?
 21:   */
 22:   if (x1 < 0 && x2 < 0 && x3 < 0) return(0);
 23:   if (y_1 < 0 && y2 < 0 && y3 < 0) return(0);
 24:   if (x1 > win->w && x2 > win->w && x3 > win->w) return(0);
 25:   if (y_1 > win->h && y2 > win->h && y3 > win->h) return(0);

 27:   t1 = t1 << SHIFT_VAL;
 28:   t2 = t2 << SHIFT_VAL;
 29:   t3 = t3 << SHIFT_VAL;

 31:   /* Sort the vertices */
 32: #define SWAP(a,b) {int _a; _a=a; a=b; b=_a;}
 33:   if (y_1 > y2) {
 34:     SWAP(y_1,y2);SWAP(t1,t2); SWAP(x1,x2);
 35:   }
 36:   if (y_1 > y3) {
 37:     SWAP(y_1,y3);SWAP(t1,t3); SWAP(x1,x3);
 38:   }
 39:   if (y2 > y3) {
 40:     SWAP(y2,y3);SWAP(t2,t3); SWAP(x2,x3);
 41:   }
 42:   /* This code is decidely non-optimal; it is intended to be a start at
 43:    an implementation */

 45:   if (y2 != y_1) R_y2_y_1 = 1.0/((double)(y2-y_1));
 46:   else R_y2_y_1 = 0.0;
 47:   if (y3 != y_1) R_y3_y_1 = 1.0/((double)(y3-y_1));
 48:   else R_y3_y_1 = 0.0;
 49:   t2_t1 = t2 - t1;
 50:   x2_x1 = x2 - x1;
 51:   t3_t1 = t3 - t1;
 52:   x3_x1 = x3 - x1;
 53:   for (y=y_1; y<=y2; y++) {
 54:     /* PetscDraw a line with the correct color from t1-t2 to t1-t3 */
 55:     /* Left color is (y-y_1)/(y2-y_1) * (t2-t1) + t1 */
 56:     lfrac = ((double)(y-y_1)) * R_y2_y_1;
 57:     lc    = (int)(lfrac * (t2_t1) + t1);
 58:     lx    = (int)(lfrac * (x2_x1) + x1);
 59:     /* Right color is (y-y_1)/(y3-y_1) * (t3-t1) + t1 */
 60:     rfrac = ((double)(y - y_1)) * R_y3_y_1;
 61:     rc    = (int)(rfrac * (t3_t1) + t1);
 62:     rx    = (int)(rfrac * (x3_x1) + x1);
 63:     /* PetscDraw the line */
 64:     rc_lc = rc - lc;
 65:     rx_lx = rx - lx;
 66:     if (rx > lx) {
 67:       for (xx=lx; xx<=rx; xx++) {
 68:         c = (((xx-lx) * (rc_lc)) / (rx_lx) + lc) >> SHIFT_VAL;
 69:         PetscDrawXiSetColor(win,c);
 70:         XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,xx,y);
 71:       }
 72:     } else if (rx < lx) {
 73:       for (xx=lx; xx>=rx; xx--) {
 74:         c = (((xx-lx) * (rc_lc)) / (rx_lx) + lc) >> SHIFT_VAL;
 75:         PetscDrawXiSetColor(win,c);
 76:         XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,xx,y);
 77:       }
 78:     } else {
 79:       c = lc >> SHIFT_VAL;
 80:       PetscDrawXiSetColor(win,c);
 81:       XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,lx,y);
 82:     }
 83:   }

 85:   /* For simplicity,"move" t1 to the intersection of t1-t3 with the line y=y2.
 86:      We take advantage of the previous iteration. */
 87:   if (y2 >= y3) return(0);
 88:   if (y_1 < y2) {
 89:     t1  = rc;
 90:     y_1 = y2;
 91:     x1  = rx;

 93:     t3_t1 = t3 - t1;
 94:     x3_x1 = x3 - x1;
 95:   }
 96:   t3_t2 = t3 - t2;
 97:   x3_x2 = x3 - x2;
 98:   if (y3 != y2) R_y3_y2 = 1.0/((double)(y3-y2));
 99:   else R_y3_y2 = 0.0;
100:   if (y3 != y_1) R_y3_y_1 = 1.0/((double)(y3-y_1));
101:   else R_y3_y_1 = 0.0;

103:   for (y=y2; y<=y3; y++) {
104:     /* PetscDraw a line with the correct color from t2-t3 to t1-t3 */
105:     /* Left color is (y-y_1)/(y2-y_1) * (t2-t1) + t1 */
106:     lfrac = ((double)(y-y2)) * R_y3_y2;
107:     lc    = (int)(lfrac * (t3_t2) + t2);
108:     lx    = (int)(lfrac * (x3_x2) + x2);
109:     /* Right color is (y-y_1)/(y3-y_1) * (t3-t1) + t1 */
110:     rfrac = ((double)(y - y_1)) * R_y3_y_1;
111:     rc    = (int)(rfrac * (t3_t1) + t1);
112:     rx    = (int)(rfrac * (x3_x1) + x1);
113:     /* PetscDraw the line */
114:     rc_lc = rc - lc;
115:     rx_lx = rx - lx;
116:     if (rx > lx) {
117:       for (xx=lx; xx<=rx; xx++) {
118:         c = (((xx-lx) * (rc_lc)) / (rx_lx) + lc) >> SHIFT_VAL;
119:         PetscDrawXiSetColor(win,c);
120:         XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,xx,y);
121:       }
122:     } else if (rx < lx) {
123:       for (xx=lx; xx>=rx; xx--) {
124:         c = (((xx-lx) * (rc_lc)) / (rx_lx) + lc) >> SHIFT_VAL;
125:         PetscDrawXiSetColor(win,c);
126:         XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,xx,y);
127:       }
128:     } else {
129:       c = lc >> SHIFT_VAL;
130:       PetscDrawXiSetColor(win,c);
131:       XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,lx,y);
132:     }
133:   }
134:   return(0);
135: }