#include "liblocky.h"

#include <assert.h>


void blky_image_convert_to_normalized_coord(
    const double verts[8], double* x, double* y) {
  assert(0 <= *x && *x < 1);
  assert(0 <= *y && *y < 1);

  const double rx = 1-*x, ry = 1-*y;

  const double top_xf = *x*verts[6] + rx*verts[0];
  const double bot_xf = *x*verts[4] + rx*verts[2];

  const double lef_yf = *y*verts[3] + ry*verts[1];
  const double rig_yf = *y*verts[5] + ry*verts[7];

  const double ans_x = *y*bot_xf + ry*top_xf;
  const double ans_y = *x*rig_yf + rx*lef_yf;

  *x = ans_x;
  *y = ans_y;
}

uint64_t blky_image_offset(
    uint32_t w, uint32_t h, const double verts[8], double x, double y) {
  blky_image_convert_to_normalized_coord(verts, &x, &y);
  const uint32_t xi = (uint32_t) (x*w);
  const uint32_t yi = (uint32_t) (y*h);
  return yi*w + xi;
}