wu_water()

void wu_water	(	uint8_t *const	buf,
		uint16_t	x,
		uint16_t	y,
		uint8_t	bright )

Definition at line 141 of file FxWater.h.

                                                                           {
  // extract the fractional parts and derive their inverses
  uint8_t xx = x & 0xff, yy = y & 0xff, ix = 255 - xx, iy = 255 - yy;
  // calculate the intensities for each affected pixel
  #define WU_WEIGHT(a, b) ((uint8_t)(((a) * (b) + (a) + (b)) >> 8))
  uint8_t wu[4] = {WU_WEIGHT(ix, iy), WU_WEIGHT(xx, iy),
                   WU_WEIGHT(ix, yy), WU_WEIGHT(xx, yy)
                  };
  #undef WU_WEIGHT
  // multiply the intensities by the colour, and saturating-add them to the pixels
  for (uint8_t i = 0; i < 4; i++) {
    uint8_t local_x = (x >> 8) + (i & 1);
    uint8_t local_y = (y >> 8) + ((i >> 1) & 1);
    uint16_t xy = WATERWIDTH * local_y + local_x;
    if (xy >= WATERWIDTH * WATERHEIGHT) continue;
    uint16_t this_bright = bright * wu[i];
    buf[xy] = qadd8(buf[xy], this_bright >> 8);
  }
}

References qadd8(), WATERHEIGHT, WATERWIDTH, WU_WEIGHT, x, xy(), and y.

Referenced by loop().

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