Function DrawCrescent

xgeneral.cpp:1050–1119

// part may be rotated by the specified number of degrees.

void DrawCrescent(int x1, int y1, int x2, int y2, real rProp, real rRotate,
  KI ki0, KI ki1)
{
  real xc, yc, rSq, dxy, rx, ry, dx, dy, dx2, dy2, rS, rC;
  int x, y, xPrev;
  KI ki, kiPrev;

  // Can only draw up to a half Moon crescent. Any greater means to draw a
  // crescent coming in from the inverse angle with the two colors reversed.
  if (rProp <= 0.5)
    rProp = 1.0 - rProp*2.0;
  else {
    rProp = (rProp - 0.5)*2.0;
    rRotate += rDegHalf;
    SwapN(ki0, ki1);
  }

  // Initialize variables.
  xc = (real)(x1 + x2) / 2.0; yc = (real)(y1 + y2) / 2.0;
  rx = (real)(x2 - x1) / 2.0; ry = (real)(y2 - y1) / 2.0;
  rSq = Sq(rx) + rx/2.0;
  dxy = rx / ry;
  RotateR2Init(rS, rC, rRotate);
  x1 = Max(x1, 0); x2 = Min(x2, gs.xWin-1);
  y1 = Max(y1, 0); y2 = Min(y2, gs.yWin-1);

  // Draw one row of the ellipse at a time.
  for (y = y1; y <= y2; y++) {
    xPrev = ki = kiPrev = ~0;
    for (x = x1; x <= x2; x++) {
      dx = (real)x - xc;
      dy = (real)y - yc;
      if (rx != ry)
        dy *= dxy;
      if (Sq(dx) + Sq(dy) > rSq) {
        if (xPrev != ~0)
          break;
        continue;
      }
      if (rRotate != 0.0) {
        // Fast rotation if doing a rotated ellipse.
        RotateR2(dx, dy, dx2, dy2, rS, rC);
      } else {
        dx2 = dx; dy2 = dy;
      }
      ki = ki1;
      if (dx2 > 0.0) {
        dx2 /= rProp;
        if (Sq(dx2) + Sq(dy2) > rSq)
          ki = ki0;
      }
      // Don't draw anything in this row until the color changes.
      if (xPrev == ~0)
        xPrev = x;
      if (kiPrev == ~0)
        kiPrev = ki;
      if (ki != kiPrev) {
        DrawColor(kiPrev);