#include <os.h>
#include "utils.h"
#include "icon.c"
#define cos1 254
#define sin1 32
#define stpsize 51

asm(".string \"PRG\"\n");

int main(void) 
{
  //set CPU to 150 Mhz
  *(volatile unsigned*) 0x900B0000 = 0x00000002;
  *(volatile unsigned*) 0x900B000C = 4;
  //allocate a buffer
  char* scrbuf = (char*) malloc(SCREEN_BYTES_SIZE);

  //map array and a blank tile
  int map[64][64];
  char blank[64][64];

  //various variables, initialized
  int px = 3072, py = 3072;  
  int dx = -256, dy = 0; 
  int plx = 0, ply = 167; 
  int w = 320, h = 240;
  int h256 = h * 256;
  int halfh = h / 2 + 1;

  //a couple of uninitialized variables
  int x, y;
  int olddx;

  //build map
  for (x = 0; x < 64; x++) {
    for (y = 0; y < 64; y++) {
      if ((x + y) % 2 == 0) {
        map[x][y] = 1;
      } else {
        map[x][y] = 0;
      }
    }
  }

  //build blank tile
  for (x = 0; x < 64; x++) {
    for (y = 0; y < 64; y++) {
      blank[x][y] = 15;
    }
  }

  //order the textures
  char* tex0 = &icon[0][0];
  char* tex1 = &blank[0][0];
  char* tex[2];
  tex[0] = tex0;
  tex[1] = tex1;

  //build a lookup table
  int ctab[h];
  for (y = 0; y < h; y++) {
    int y1 = h256 - (y << 8);
    int y2 = (y << 8) - h256 / 2;
    ctab[y] = 256 + (y1 << 8) / y2;
  }

  int redraw;
  while (!isKeyPressed(KEY_NSPIRE_ESC)) {
    redraw = 0;
    if (isKeyPressed(KEY_NSPIRE_LEFT)) {
      olddx = dx;
      dx = (dx * cos1 - dy * sin1) >> 8;
      dy = (olddx * sin1 + dy * cos1) >> 8;
      int oldplx = plx;
      plx = (plx * cos1 - ply * sin1) >> 8;
      ply = (oldplx * sin1 + ply * cos1) >> 8;
      redraw = 1;
    }
    if (isKeyPressed(KEY_NSPIRE_RIGHT)) {
      olddx = dx;
      dx = (dx * cos1 + dy * sin1) >> 8;
      dy = (-olddx * sin1 + dy * cos1) >> 8;
      int oldplx = plx;
      plx = (plx * cos1 + ply * sin1) >> 8;
      ply = (-oldplx * sin1 + ply * cos1) >> 8;
      redraw = 1;
    }
    if (isKeyPressed(KEY_NSPIRE_UP)) {
      px += (stpsize * dx) >> 8;
      py += (stpsize * dy) >> 8;
      redraw = true;
    }
    if (isKeyPressed(KEY_NSPIRE_DOWN)) {
      px -= (stpsize * dx) >> 8;
      py -= (stpsize * dy) >> 8;
      redraw = true;
    }
    if (redraw) {
      memset(scrbuf, 0xFF, SCREEN_BYTES_SIZE);
      for(x = 0; x < w - 1; x += 2) {
        int cameraX = 2 * (x << 8) / w - 256; 
        int raydx = dx + ((plx * cameraX) >> 8);
        int raydy = dy + ((ply * cameraX) >> 8);       
           
        for (y = halfh; y < h; y++) {
          int c = ctab[y];
          int floorX = ((raydx * c) >> 8) + px;
          int floorY = ((raydy * c) >> 8) + py;
          int sX = floorX >> 2, sY = floorY >> 2;
          int mX = sX >> 6, mY = sY >> 6;
          if (mX > 0 && mX < 64 && mY > 0 && mY < 64) {
            int tX = sX & 63;
            int tY = sY & 63;
            int color = (tex[map[mX][mY]])[tX + (tY << 6)];
            setPixelBuf(scrbuf, x, y, color);
            setPixelBuf(scrbuf, x + 1, y, color);
          }
        }
      }
      refresh(scrbuf);
    }
  }

  *(volatile unsigned*) 0x900B0000 = 0x00141002;
  *(volatile unsigned*) 0x900B000C = 4;
  free(scrbuf);
  return 0;
}