Zig-Zag三角遍历实现

Question

我试图按照"On the Hardware Implementation of Triangle Traversal Algorithms for Graphics Processing" (Royer, Ituero, Lopez-Vallejo, & Barrio)（第4页）实现三角形三角/光栅化的Zig-Zag遍历算法。然而，论文中的解释对我来说是违反直觉的，我无法使其发挥作用。

我试图实现一个有限状态机，但我无法弄清楚确切的状态。现在，我有（方向，e_1，e_2，e_3），其中e_n表示每个边缘的边缘测试输出。伪代码：

/// Zig Zag (not working)
int top_row = floor(fmin(y0, fmin(y1, y2)));
int bot_row = floor(fmax(y0, fmax(y1, y2)));
if (y0 > y1) {
  swap(x0, x1); swap(y0, y1);
}
if (y0 > y2) {
  swap(x0, x2); swap(y0, y2);
}
if (y1 > y2) {
  swap(x1, x2); swap(y1, y2);
}
assert(top_row == floor(y0));
assert(bot_row == floor(y2));

bool direction = true;
bool changed = false;
int x = floor(x0); int y = floor(y0);
while (y <= bot_row) {
  bool e1, e2, e3;
  e1 = edge_test((float)x+0.5, (float)y+0.5, x0, y0, x1, y1) < 0.0f;
  e2 = edge_test((float)x+0.5, (float)y+0.5, x1, y1, x2, y2) < 0.0f;
  e3 = edge_test((float)x+0.5, (float)y+0.5, x2, y2, x0, y0) < 0.0f;

  if ((e1 == e2) && (e2 == e3)) {
    if ( x < 0 || x >= width ) continue;
    if ( y < 0 || y >= height ) continue;
    samplebuffer[y][x].fill_pixel(color);

    if (direction) x++;
    else x--;
  } else if (changed) {
    y++;
    changed = false;
  } else {
    direction = !direction;
    changed = true;
    if (direction) x++;
    else x--;
  }
}

任何帮助将不胜感激！

编辑：到目前为止我的努力： 边缘测试正常工作时，图表中只有少数部分被栅格化。

Run > External Tools > External Tools Configurations ...

Answer 1

我如何看到状态机：

Dir = +1 / -1

State 0: (moving inside)
EdgeTest: 
    0 => State 1 ;  y++
    1 => State 0 ;  x = x + Dir

State 1: (outside)
EdgeTest: 
    0 => State 3 ;  Dir = - Dir
    1 => State 2 ;

State 2: (inside moving the same dir)
EdgeTest: 
    0 => State 3 ;  Dir = - Dir
    1 => State 2 ;  x= x + Dir

State 3: (outside)
EdgeTest: 
    0 => State 3 ; x = x + Dir
    1 => State 0 ;