//====================================================================================
// bruteforce2.cpp : brute force evaluation of sphere pixel coverage (scan-conversion)
//   and depth-value evaluation using combined method in SCREEN SPACE.
//====================================================================================
#include "fbppm.hpp"
#include <math.h>

// THE "MOCK" FRAMEBUFFER
int WW=256, WH=256;
FrameBufferPPM fb(WW,WH);

//------------------------------------------------------------------------------------
// Paraboloid function that fits the points: (a+r,b,MaxZ), (a-r,b,MaxZ), (a,b+r,MaxZ),
// (a,b-r,MaxZ), and minimum at (a,b,MinZ) extending to infinity in +Z.
// Evaluates z for a given (x,y).
//------------------------------------------------------------------------------------
float Depth(int x, int y, int a, int b, float r, float MinZ, float MaxZ)
{
  if (r>0)
  {
    float xa=x-a, yb=y-b;
    float fxy = (MaxZ-MinZ)*(xa*xa + yb*yb)/(r*r) + MinZ;
    return (fxy);
  }
  else return(MaxZ+1); // RETURN INVALID VALUE
}


//------------------------------------------------------------------------------------
// scan-converts sphere given center (a,b) in screen space, pixel radius,
// Min and Max depth Z-value (Max is "deeper").
//------------------------------------------------------------------------------------
void BruteForceSphere(int a, int b, float r, float MinZ, float MaxZ)
{
  for (int x=0; x<WW; x++)
    for (int y=0; y<WH; y++)                   // FOR EVERY PIXEL (x,y)
    {
      int PixelIsEnabled=0;                    // SET ENABLE FLAG TO FALSE
      float depth = Depth(x,y,a,b,r,MinZ,MaxZ);// CALCULATE DEPTH
      if (depth<=MaxZ) PixelIsEnabled=1;       // CHECK IF PIXEL IS INSIDE THE CIRCLE
                                               // DO Zbuffer DEPTH TEST HERE!
      if (PixelIsEnabled)                      // DRAW THE PIXEL IF ENABLED
      {
        float C=1-depth;
        fb.SetForeground(C,C,C);
        fb.SetPixel(x,y);
      }
    }
}

void main()
{
  int NumSphereTiles=2;

  float TileWidth = (float)WW/NumSphereTiles;
  float TileHeight = (float)WH/NumSphereTiles;
  float r = (TileWidth+TileHeight)*0.25; // CIRCLE RADIUS
  float a,b;                             // CIRCLE CENTER
  b=TileHeight*0.5;
  for (int i=0; i<NumSphereTiles; i++)
  {
    a=TileWidth*0.5;
    for (int j=0; j<NumSphereTiles; j++)
    {
      BruteForceSphere(a,b,r,0,1);
      a+=TileWidth;
    }
    b+=TileHeight;
  }

  fb.MakePPM("output.ppm");
}