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

PETSC_INTERN PetscErrorCode PetscDrawInterpolatedTriangle_X(PetscDraw_X*,int,int,int,int,int,int,int,int,int);

#define SHIFT_VAL 6

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)
{
  PetscReal rfrac,lfrac;
  PetscReal R_y2_y_1,R_y3_y_1,R_y3_y2;
  int       lc,rc = 0,lx,rx = 0,xx,y,c;
  int       rc_lc,rx_lx,t2_t1,x2_x1,t3_t1,x3_x1,t3_t2,x3_x2;

  PetscFunctionBegin;
  /*
        Is triangle even visible in window?
  */
  if (x1 < 0 && x2 < 0 && x3 < 0) PetscFunctionReturn(0);
  if (y_1 < 0 && y2 < 0 && y3 < 0) PetscFunctionReturn(0);
  if (x1 > win->w && x2 > win->w && x3 > win->w) PetscFunctionReturn(0);
  if (y_1 > win->h && y2 > win->h && y3 > win->h) PetscFunctionReturn(0);

  t1 = t1 << SHIFT_VAL;
  t2 = t2 << SHIFT_VAL;
  t3 = t3 << SHIFT_VAL;

  /* Sort the vertices */
#define SWAP(a,b) {int _a; _a=a; a=b; b=_a;}
  if (y_1 > y2) {
    SWAP(y_1,y2);SWAP(t1,t2); SWAP(x1,x2);
  }
  if (y_1 > y3) {
    SWAP(y_1,y3);SWAP(t1,t3); SWAP(x1,x3);
  }
  if (y2 > y3) {
    SWAP(y2,y3);SWAP(t2,t3); SWAP(x2,x3);
  }
  /* This code is decidely non-optimal; it is intended to be a start at
   an implementation */

  if (y2 != y_1) R_y2_y_1 = 1.0/((double)(y2-y_1));
  else R_y2_y_1 = 0.0;
  if (y3 != y_1) R_y3_y_1 = 1.0/((double)(y3-y_1));
  else R_y3_y_1 = 0.0;
  t2_t1 = t2 - t1;
  x2_x1 = x2 - x1;
  t3_t1 = t3 - t1;
  x3_x1 = x3 - x1;
  for (y=y_1; y<=y2; y++) {
    /* PetscDraw a line with the correct color from t1-t2 to t1-t3 */
    /* Left color is (y-y_1)/(y2-y_1) * (t2-t1) + t1 */
    lfrac = ((double)(y-y_1)) * R_y2_y_1;
    lc    = (int)(lfrac * (t2_t1) + t1);
    lx    = (int)(lfrac * (x2_x1) + x1);
    /* Right color is (y-y_1)/(y3-y_1) * (t3-t1) + t1 */
    rfrac = ((double)(y - y_1)) * R_y3_y_1;
    rc    = (int)(rfrac * (t3_t1) + t1);
    rx    = (int)(rfrac * (x3_x1) + x1);
    /* PetscDraw the line */
    rc_lc = rc - lc;
    rx_lx = rx - lx;
    if (rx > lx) {
      for (xx=lx; xx<=rx; xx++) {
        c = (((xx-lx) * (rc_lc)) / (rx_lx) + lc) >> SHIFT_VAL;
        PetscDrawXiSetColor(win,c);
        XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,xx,y);
      }
    } else if (rx < lx) {
      for (xx=lx; xx>=rx; xx--) {
        c = (((xx-lx) * (rc_lc)) / (rx_lx) + lc) >> SHIFT_VAL;
        PetscDrawXiSetColor(win,c);
        XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,xx,y);
      }
    } else {
      c = lc >> SHIFT_VAL;
      PetscDrawXiSetColor(win,c);
      XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,lx,y);
    }
  }

  /* For simplicity,"move" t1 to the intersection of t1-t3 with the line y=y2.
     We take advantage of the previous iteration. */
  if (y2 >= y3) PetscFunctionReturn(0);
  if (y_1 < y2) {
    t1  = rc;
    y_1 = y2;
    x1  = rx;

    t3_t1 = t3 - t1;
    x3_x1 = x3 - x1;
  }
  t3_t2 = t3 - t2;
  x3_x2 = x3 - x2;
  if (y3 != y2) R_y3_y2 = 1.0/((double)(y3-y2));
  else R_y3_y2 = 0.0;
  if (y3 != y_1) R_y3_y_1 = 1.0/((double)(y3-y_1));
  else R_y3_y_1 = 0.0;

  for (y=y2; y<=y3; y++) {
    /* PetscDraw a line with the correct color from t2-t3 to t1-t3 */
    /* Left color is (y-y_1)/(y2-y_1) * (t2-t1) + t1 */
    lfrac = ((double)(y-y2)) * R_y3_y2;
    lc    = (int)(lfrac * (t3_t2) + t2);
    lx    = (int)(lfrac * (x3_x2) + x2);
    /* Right color is (y-y_1)/(y3-y_1) * (t3-t1) + t1 */
    rfrac = ((double)(y - y_1)) * R_y3_y_1;
    rc    = (int)(rfrac * (t3_t1) + t1);
    rx    = (int)(rfrac * (x3_x1) + x1);
    /* PetscDraw the line */
    rc_lc = rc - lc;
    rx_lx = rx - lx;
    if (rx > lx) {
      for (xx=lx; xx<=rx; xx++) {
        c = (((xx-lx) * (rc_lc)) / (rx_lx) + lc) >> SHIFT_VAL;
        PetscDrawXiSetColor(win,c);
        XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,xx,y);
      }
    } else if (rx < lx) {
      for (xx=lx; xx>=rx; xx--) {
        c = (((xx-lx) * (rc_lc)) / (rx_lx) + lc) >> SHIFT_VAL;
        PetscDrawXiSetColor(win,c);
        XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,xx,y);
      }
    } else {
      c = lc >> SHIFT_VAL;
      PetscDrawXiSetColor(win,c);
      XDrawPoint(win->disp,PetscDrawXiDrawable(win),win->gc.set,lx,y);
    }
  }
  PetscFunctionReturn(0);
}