/* Open and filled triangles and quadrilaterals - see http://www.technoblogy.com/show?3ZYQ

   David Johnson-Davies - www.technoblogy.com - 15th August 2022
   
   CC BY 4.0
   Licensed under a Creative Commons Attribution 4.0 International license: 
   http://creativecommons.org/licenses/by/4.0/
*/

#define swap(a, b) { a = a ^ b; b = b ^ a; a = a ^ b; }

void DrawQuad(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1,
              uint16_t x2, uint16_t y2, uint16_t x3, uint16_t y3) {
  MoveTo(x0, y0); DrawTo(x1, y1); DrawTo(x2, y2); DrawTo(x3, y3); DrawTo(x0, y0);
}

void DrawTriangle(uint16_t x0, uint16_t y0, uint16_t x1,
                  uint16_t y1, uint16_t x2, uint16_t y2) {
  MoveTo(x0, y0); DrawTo(x1, y1); DrawTo(x2, y2); DrawTo(x0, y0);
}

void FillTriangle(int16_t x0, int16_t y0, int16_t x1,
                  int16_t y1, int16_t x2, int16_t y2) {
  // Sort coordinates by y order (y2 >= y1 >= y0)
  if (y0 > y1) { swap(y0, y1); swap(x0, x1); }
  if (y1 > y2) { swap(y1, y2); swap(x1, x2); }
  if (y0 > y1) { swap(y0, y1); swap(x0, x1); }
  TriangleQuad(x0, y0, x1, y1, x2, y2, x2, y2);
}

void FillQuad(int16_t x0, int16_t y0, int16_t x1, int16_t y1,
              int16_t x2, int16_t y2, int16_t x3, int16_t y3) {
  // Sort coordinates by y order (y3 >= y2 >= y1 >= y0)
  if (y0 > y1) { swap(y0, y1); swap(x0, x1); }
  if (y2 > y3) { swap(y2, y3); swap(x2, x3); }
  if (y1 > y3) { swap(y1, y3); swap(x1, x3); }
  if (y0 > y2) { swap(y0, y2); swap(x0, x2); }
  if (y1 > y2) { swap(y1, y2); swap(x1, x2); }
  TriangleQuad(x0, y0, x1, y1, x2, y2, x3, y3);
}
  
void TriangleQuad(int16_t x0, int16_t y0, int16_t x1, int16_t y1,
                  int16_t x2, int16_t y2, int16_t x3, int16_t y3) {
  // Coordinates already in y order (y3 >= y2 >= y1 >= y0)
  int16_t a, b, y;

  // Special case?
  int16_t x4 = x0 + (x3 - x0) * (y1 - y0) / (y3 - y0);
  int16_t x5 = x0 + (x3 - x0) * (y2 - y0) / (y3 - y0);

  if ((x5 > x2) == (x4 > x1)) {
    swap(x2, x5);
  } else { // Kite
    x4 = x0 + (x2 - x0) * (y1 - y0) / (y2 - y0);
    x5 = x1 + (x3 - x1) * (y2 - y1) / (y3 - y1);
  }
  
  // Fill bottom section
  for (y = y0; y <= y1; y++) {
    a = x0 + (x4 - x0) * (y - y0) / (y1 - y0);
    b = x0 + (x1 - x0) * (y - y0) / (y1 - y0);
    if (a > b) swap(a, b);
    // MoveTo(a, y); DrawTo(b, y);
    MoveTo(a, y); FillRect(b - a + 1, 1);
  }

  // Fill middle section
  for (; y <= y2; y++) {
    a = x4 + (x2 - x4) * (y - y1) / (y2 - y1);
    b = x1 + (x5 - x1) * (y - y1) / (y2 - y1);
    if (a > b) swap(a, b);
    // MoveTo(a, y); DrawTo(b, y);
    MoveTo(a, y); FillRect(b - a + 1, 1);
  }

  // Fill top section
  for (; y <= y3; y++) {
    a = x2 + (x3 - x2) * (y - y2) / (y3 - y2);
    b = x5 + (x3 - x5) * (y - y2) / (y3 - y2);
    if (a > b) swap(a, b);
    // MoveTo(a, y); DrawTo(b, y);
    MoveTo(a, y); FillRect(b - a + 1, 1);
  }
}

// Demo **********************************************

void Cubes () {
  int h = 21, w = 36, x0  = 120, y0 = 100;
  for (int y=y0, i=2; y<=y0+h*6; y=y+h*3, i--) {
    for (int x=x0-w*i; x<=x0+w*i; x = x+w*2) {
      fore = Colour(255, 8, 8);   // Red
      FillQuad(x, y, x - w, y - h, x, y - h*2, x + w, y - h);
      fore = Colour(16, 16, 255); // Blue
      FillQuad(x - w, y - h, x, y - h*2, x, y - h*4, x - w, y - h*3);
      fore = Colour(192, 128, 0); // Orange
      FillQuad(x, y - h*2, x, y - h*4, x + w, y - h*3 ,x + w, y - h);
    }
  }
}