examples/line_segment.cpp

#include <cstdlib>
#include <iostream>
#include <fstream>
#include <cmath>
#include "Board.h"
using namespace LibBoard;

const int PIXEL_WIDTH=30;
const int IMAGE_HALF_SIDE=15;  // In pixels...

namespace {
float myRound(float x)
{
  return (x>=0)?floor(x+0.5):ceil(x-0.5);
}

template<typename T>
void mySwap( T & a, T & b )
{
  T tmp = a;
  a = b;
  b = tmp;
}
}

void drawPixel( Board & board, int x, int y )
{
  board.drawRectangle(PIXEL_WIDTH*(x-0.5),PIXEL_WIDTH*(y+0.5),PIXEL_WIDTH,PIXEL_WIDTH);
}

/*
 * Draws a rasterization of a line segment, i.e., the set of pixels
 * that intersect the segment (and the Euclidean line segment as well).
 */
void drawLine( Board & board, float x1, float y1, float x2, float y2 )
{
  // Draw the Euclidean line in the real plane.
  board.setPenColorRGBi(255,0,0);
  board.drawArrow(x1*PIXEL_WIDTH,y1*PIXEL_WIDTH,x2*PIXEL_WIDTH,y2*PIXEL_WIDTH);
  board.fillCircle(x1*PIXEL_WIDTH,y1*PIXEL_WIDTH,2);
  board.fillCircle(x2*PIXEL_WIDTH,y2*PIXEL_WIDTH,2);
  board.setPenColorRGBi(0,0,0);

  // Draw the rasterized line.
  bool permute = false;
  float slope = (y2-y1)/(x2-x1);
  if ( std::abs(slope) > 1 ) {
    permute = true;
    mySwap(x1,y1);
    mySwap(x2,y2);
    slope = (y2-y1)/(x2-x1);
  }
  if ( myRound(x1) == myRound(x2) ) {
    drawPixel( board, myRound(x1), myRound(y1) );
    drawPixel( board, myRound(x2), myRound(y2) );
    return;
  }
  int xStep = (x1<x2)?+1:-1;
  int x = myRound(x1);
  int xStop = myRound(x2);
  // Draw pixel(s) for x=round(x1)
  if ( permute ) {
    drawPixel( board, myRound(y1), x);
  } else {
    drawPixel( board, x, myRound(y1));
  }
  int y = myRound( slope*((x + xStep*0.5)-x1) + y1 );
  if ( y != myRound(y1) ) {
    if ( permute ) {
      drawPixel( board, y, x );
    } else {
      drawPixel( board, x, y );
    }
  }
  // Traverse all xs
  if ( permute ) {
    do {
      x += xStep;
      float yA = myRound( slope*((x - 0.5)-x1) + y1 );
      drawPixel( board, yA, x );
      float yB = myRound( slope*((x + 0.5)-x1) + y1 );
      if ( yB != yA ) { drawPixel( board, yB, x ); }
    } while ( x != xStop );
  } else {
    do {
      x += xStep;
      float yA = myRound( slope*((x - 0.5)-x1) + y1 );
      drawPixel( board, x, yA );
      float yB = myRound( slope*((x + 0.5)-x1) + y1 );
      if ( yB != yA ) { drawPixel( board, x, yB ); }
    } while ( x != xStop );
  }
}

int main( int, char *[] )
{
  Board board;
  const int side =  PIXEL_WIDTH * IMAGE_HALF_SIDE;

  board.setPenColorRGBi( 0, 0, 0 );
  board.setLineWidth( 1.0 );
  board.setLineCap(Shape::RoundCap);
  board.drawLine(-side,0,side,0);
  board.drawLine(0,-side,0,side);

  // Slope < 1, forward and backward
  drawLine(board, -12.25, 1.2, 5.34, 9.23 );
  drawLine(board, 0.3, -3.2, 8.4, -6.7 );
  drawLine(board, -2.3, -3.2, -12.4, -7.7 );
  // Slope > 1
  drawLine(board, 7.6, 1.2, 10.5, 12.1 );

  board.saveEPS( "line_segment.eps" );

  board.scaleToWidth(25,Board::UseLineWidth);
  board.saveSVG( "line_segment.svg", Board::BoundingBox, 0.0, Board::UCentimeter );
}