axissort.cpp

Beginning Direct3D Game Programming源代码Part3chapter12

#include <vector>
#include <algorithm>
#include <iostream>

class SpriteRect
{
public:
  SpriteRect(int x_, int y_, int w_, int h_)
    : x(x_), y(y_), w(w_), h(h_) {}
  // Position
  int x,y;
  // Size
  int w,h;
};

typedef std::vector<SpriteRect>           SpriteVector;
typedef std::vector<SpriteRect>::iterator SpriteIterator;


void FullCollisionTest(const SpriteRect& s1, const SpriteRect& s2)
{
  // Here we'll plug in the full collision test.
  std::cout << "Testing for collision between: " <<
    s1.x << ',' << s1.y << ',' << s1.w << ',' << s1.h << "   and   " <<
    s2.x << ',' << s2.y << ',' << s2.w << ',' << s2.h << std::endl;
}

// Predicate function.  Used in the sort to determine
// how to order two sprite objects.
bool PredX(const SpriteRect& s1, const SpriteRect& s2)
{
  return (s1.x < s2.x);
}

// Check if two sprites intersect in the X axis
// This assumes that  s1.x <= s2.x
bool IntersectX(const SpriteRect& s1, const SpriteRect& s2)
{
  return (s2.x < s1.x+s1.w);
}

void axis_sort(SpriteIterator begin, SpriteIterator end)
{
  // Sort the objects, according to the X axis
  std::sort(begin,end,PredX);
  
  // Go over all objects, according to sorted order
  for(;begin!=end;begin++)
  {
    // Go over all adjacent objects, until no intersection
    // in the X axis is found.
    for(SpriteIterator i=begin+1;i!=end;i++)
    {
      if (IntersectX(*begin,*i)) 
      {
        // Intersection in X means possible collision
        FullCollisionTest(*begin,*i);
      }
      else 
        break;
    }
  }
}

// Test example
int main(int argc, char* argv[])
{
  SpriteVector objects;
  objects.push_back(SpriteRect(20,6,3,2));
  objects.push_back(SpriteRect(7,9,3,2));
  objects.push_back(SpriteRect(19,1,3,2));
  objects.push_back(SpriteRect(2,4,3,2));
  objects.push_back(SpriteRect(18,7,3,2));
  objects.push_back(SpriteRect(12,2,3,2));
  axis_sort(objects.begin(),objects.end());
  return 0;
}