Upsilon/kandinsky/src/context_polygon.cpp

#include <kandinsky/context.h>
#include <assert.h>
#include <math.h>

void KDContext::fillPolygon(KDCoordinate pointsX[], KDCoordinate pointsY[], int numberOfPoints, KDColor color)
{
  //The used algorithm is the scan-line algorithm

  KDCoordinate top = KDCOORDINATE_MAX;
  KDCoordinate bottom = KDCOORDINATE_MIN;
  KDCoordinate right = m_clippingRect.width();
  KDCoordinate left = 0;

  for (int i = 0; i < numberOfPoints; i++) {
    if (pointsY[i] < top) {
      top = pointsY[i];
    }
    if (pointsY[i] > bottom) {
      bottom = pointsY[i];
    }
  }

  if (top < 0) {
    top = 0;
  }
  if (bottom > m_clippingRect.height()) {
    bottom = m_clippingRect.height();
  }


  for (int y=top; y<=bottom; y++) {

    int switches=0;
    KDCoordinate switchesX[KDContext::k_polygonMaxNumberOfPoints];
    int lastPointIndex = numberOfPoints-1;

    for (int i=0; i<numberOfPoints; i++) {
      if (((pointsY[i]<=y && pointsY[lastPointIndex]>=y) || (pointsY[lastPointIndex]<= y && pointsY[i]>=y)) && pointsY[i] != pointsY[lastPointIndex]) {
        switchesX[switches++] = (int) round(pointsX[i]+1.0*(y-pointsY[i])/(pointsY[lastPointIndex]-pointsY[i])*(pointsX[lastPointIndex]-pointsX[i])); 
      }
      lastPointIndex=i; 
    }

    //Sorting switches by a bubble sort
    int i=0;
    while (i<switches-1) {
      if (switchesX[i]>switchesX[i+1]) {
        KDCoordinate temp = switchesX[i]; 
        switchesX[i]=switchesX[i+1]; 
        switchesX[i+1]=temp; 
        if (i) i--; 
      }
      else {
        i++; 
      }
    }

    for (i=0; i<switches; i+=2) {
      if (switchesX[i]>=right) {
        break;
      }
      if (switchesX[i+1]>left) {
          fillRect( KDRect( switchesX[ i ] , y, switchesX[ i+1 ] - switchesX[ i ], 1 ), color ) ;
      }
    }
  }
}