如何在处理中使用 Bresenham 的线算法在网格中创建一条线

Question

我想使用 Bresenham 的 algorithm 创建一条线，但唯一有效的线是从左到右的水平线，向上的线根本不起作用，对角线向下绘制的线出现在错误的位置，线条越垂直，鼠标位置变化与绘制的线条之间的距离越大，最多为 3 个单元格。我正在使用 java 和处理库。这是所有相关 code 的链接。主要代码是这样的：

void lineDrawing()
{
  int deltaX = mouseNewCordX - mouseOldCordX, deltaY = mouseNewCordY - mouseOldCordY;
  int gradient = deltaY + deltaY, error = gradient - deltaX;

  if (abs(deltaY) < abs(deltaX))
  {
    if (mouseOldCordX > mouseNewCordX)
    {
      plotLineLow(mouseOldCordX, mouseOldCordY, deltaX, deltaY, gradient, error);
    } else 
    {
      plotLineLow(mouseNewCordX, mouseNewCordY, deltaX, deltaY, gradient, error);
    }
  } else 
  {
    if (mouseOldCordY > mouseNewCordY)
    {
      plotLineHigh(mouseOldCordX, mouseOldCordY, deltaX, deltaY, gradient, error);
    } else
    {
      plotLineHigh(mouseNewCordX, mouseNewCordY, deltaX, deltaY, gradient, error);
    }
  }
}

void plotLineLow(int x0, int y0, int deltaX, int deltaY, int gradient, int error)
{
  int yIncrease = 1;

  if (deltaY < 0)
  {
    yIncrease = -1;
    deltaY = -deltaY;
  }

  for (int x = mouseOldCordX; x <= mouseNewCordX; x += 1)
  {

    world[x][y0].state = selectedState;

    error += gradient;

    if (error >= 0)
    {
      y0 += yIncrease;
      error -= (deltaX + deltaX);
    }
  }
}

void plotLineHigh(int x0, int y0, int deltaX, int deltaY, int gradient, int error)
{
  int xIncrease = 1;

  if (deltaX < 0)
  {
    xIncrease = -1;
    deltaX = -deltaX;
  }

  for (int y = mouseOldCordY; y <= mouseNewCordY; y += 1)
  {

    world[x0][y].state = selectedState;

    error += gradient;

    if (error >= 0)
    {
      x0 += xIncrease;
      error -= (deltaY + deltaY);
    }
  }
}

Answer 1

我能够使用维基百科创建一个有效的代码：

    void lineDrawing()
    {
      int xIncrease = mouseOldCordX < mouseNewCordX ? 1 : -1;  
      int yIncrease = mouseOldCordY < mouseNewCordY ? 1 : -1;
      int deltaX =  abs(mouseNewCordX - mouseOldCordX);
      int deltaY = -abs(mouseNewCordY - mouseOldCordY);
      int error = deltaX + deltaY;
    
      while (true) 
      {
        world[mouseOldCordX][mouseOldCordY].state = selectedState;
    
        if ((mouseOldCordX == mouseNewCordX) && (mouseOldCordY == mouseNewCordY)) break;
    
        int doubleError = 2 * error;
    
        if (doubleError >= deltaY) 
        { 
          error += deltaY;
          mouseOldCordX += xIncrease;
        }
    
        if (doubleError <= deltaX)
        {
          error += deltaX;
          mouseOldCordY += yIncrease;
        }
      }
    }