// Use the idea from the code in following links
// https://en.wikipedia.org/wiki/Xiaolin_Wu%27s_line_algorithm
// https://rosettacode.org/wiki/Xiaolin_Wu%27s_line_algorithm#C.23
public void XiaolinWu(Line line2D, Color color)
{
Point p1 = line2D.p1;
Point p2 = line2D.p2;
if (line2D.isPoint())
{
bitmap.SetPixel(p1.X, p1.Y, color);
return;
}
int Dx = p2.X - p1.X;
int Dy = p2.Y - p1.Y;
int x_incre, y_incre;
float gradient;
// if Dy, Dx is negative -> change step in each increment to -1
y_incre = Dy < 0 ? -1 : 1;
x_incre = Dx < 0 ? -1 : 1;
// x incre faster than y incre
if (Math.Abs(Dx) > Math.Abs(Dy))
{
gradient = Math.Abs(Dy) / (float)Math.Abs(Dx) * y_incre;
int x_draw = p1.X;
float float_y = p1.Y;
while (x_draw != p2.X)
{
float f_part_y = float_y - (float)Math.Floor(float_y);
float rf_part_y = 1 - f_part_y;
int y_draw = (int)Math.Floor(float_y);
if (y_draw >= 0 && y_draw < bitmap.Height)
{
int alpha = (int)Math.Round(rf_part_y * 255);
bitmap.SetPixel(x_draw, y_draw,
Color.FromArgb(alpha, color));
}
if (y_draw + y_incre >= 0 && y_draw + y_incre < bitmap.Height)
{
int alpha = (int)Math.Round(f_part_y * 255);
bitmap.SetPixel(x_draw, y_draw + y_incre,
Color.FromArgb(alpha, color));
}
x_draw += x_incre;
float_y += gradient;
}
}
// y incre faster than x incre
else
{
gradient = Math.Abs(Dx) / (float)Math.Abs(Dy) * x_incre;
int y_draw = p1.Y;
float float_x = p1.X;
while (y_draw != p2.Y)
{
float f_part_x = float_x - (float)Math.Floor(float_x);
float rf_part_x = 1 - f_part_x;
int x_draw = (int)Math.Floor(float_x);
if (x_draw >= 0 && x_draw < bitmap.Width)
{
int alpha = (int)Math.Round(rf_part_x * 255);
bitmap.SetPixel(x_draw, y_draw,
Color.FromArgb(alpha, color));
}
if (x_draw + x_incre >= 0 && x_draw + x_incre < bitmap.Width)
{
int alpha = (int)Math.Round(f_part_x * 255);
bitmap.SetPixel(x_draw + x_incre, y_draw,
Color.FromArgb(alpha, color));
}
y_draw += y_incre;
float_x += gradient;
}
}
}
// Use the idea from the code in following links
// https://csustan.csustan.edu/~tom/Lecture-Notes/Graphics/Bresenham-Line/Bresenham-Line.pdf
public void Bresenham(Line line2D, Color color)
{
Point p1 = line2D.p1;
Point p2 = line2D.p2;
if (line2D.isPoint())
{
bitmap.SetPixel(p1.X, p1.Y, color);
return;
}
int Dx = p2.X - p1.X;
int Dy = p2.Y - p1.Y;
int x_increment, y_increment, x_draw, y_draw;
// if Dy, Dx is negative -> change step in each increment to -1
// if slope > 1 or < -1, swap Dx with Dy, x with y
if (Dy < 0)
{
Dy = -Dy;
y_increment = -1;
}
else
{
y_increment = 1;
}
if (Dx < 0)
{
Dx = -Dx;
x_increment = -1;
}
else
{
x_increment = 1;
}
// Explain Bresenham algorithm
// From Point(x_i, y_i) next to Point(x_(i+1), y)
// Need to know y near y_i or y_i + 1
// d1 = y - y_i
// d2 = (y_i + 1) - y
// if d1 - d2 < 0, y = y_i
// otherwise y = y_i + 1
//
// d1 - d2 = 2y - 2y_i - 1
// as know Point(x_(i+1), y) on the line,
// so y = (Dy/Dx) * x_(i+1) + b with b = y_0 - (Dy/Dx) * x0 and x_(i+1) = x_i + 1
// d1 - d2 = 2(Dy/Dx) * x_i - 2y_i + (2b - 1 + 2(Dy/Dx))
//
// p_i = Dx * (d1 - d2)
// d1 - d2 < 0 <=> p_i < 0 (Use p_i to avoid divide to Dx)
// p_i = 2Dy * x_i - 2Dx * y_i + (2b * Dx - Dx + 2Dy)
//
// p_(i+1) - p_i = 2Dy - 2Dx * (y_(i+1) - y_i)
//
// with p_i < 0
// y_(i+1) = y_i
// p_(i+1) = p_i + 2Dy
// with p_i >= 0
// y_(i+1) = y_i + 1
// p_(i+1) = p_i + 2Dy - 2Dx
//
// p_0 = 2Dy * x_0 - 2Dx * y_0 + (2b * Dx - Dx + 2Dy)
// with b = y_0 - (Dy/Dx) * x0
// p_0 = 2Dy - Dx
// value of x, y actually draw
x_draw = p1.X;
y_draw = p1.Y;
bitmap.SetPixel(x_draw, y_draw, color);
// error_step is p_i
int error_step;
if (Dx > Dy)
{
// init error_step with p_0
error_step = 2 * Dy - Dx;
while (x_draw != p2.X)
{
x_draw += x_increment;
if (error_step < 0)
{
error_step += 2 * Dy;
}
else
{
y_draw += y_increment;
error_step += 2 * Dy - 2 * Dx;
}
bitmap.SetPixel(x_draw, y_draw, color);
}
}
else
{
error_step = 2 * Dx - Dy;
while (y_draw != p2.Y)
{
if (error_step < 0)
{
error_step += 2 * Dx;
}
else
{
x_draw += x_increment;
error_step += 2 * Dx - 2 * Dy;
}
y_draw += y_increment;
bitmap.SetPixel(x_draw, y_draw, color);
}
}
}
// Bresenham and MidPoint draw line is actually the same
public void MidPoint(Line line2D, Color color)
{
Point p1 = line2D.p1;
Point p2 = line2D.p2;
if (line2D.isPoint())
{
bitmap.SetPixel(p1.X, p1.Y, color);
return;
}
int Dx = p2.X - p1.X;
int Dy = p2.Y - p1.Y;
int x_increment, y_increment, x_draw, y_draw;
// if Dy, Dx is negative -> change step in each increment to -1
// if slope > 1 or < -1, swap Dx with Dy, x with y
if (Dy < 0)
{
Dy = -Dy;
y_increment = -1;
}
else
{
y_increment = 1;
}
if (Dx < 0)
{
Dx = -Dx;
x_increment = -1;
}
else
{
x_increment = 1;
}
// Explain MidPoint algorithm
// in Bresenham algorithm, use d1 - d2 to determine y_(i+1)
// in MidPoint, use y_i + 1/2
//
// F(x, y) = Ax + By + C, A > 0
// F(x, y) < 0 above the line
// > 0 below the line
//
// mid point is Point(x_(i+1), y_i + 1/2)
// p_i = 2F(x_(i+1), y_i + 1/2)
// p_i < 0, line in half below mid point
// p_i > 0, line in half above mid point
//
// p_(i+1) = p_i + 2Dy - 2Dx * (y_(i+1) - y_i)
// p_0 = 2Dy - Dx
// same as Bresenham
// value of x, y actually draw
x_draw = p1.X;
y_draw = p1.Y;
bitmap.SetPixel(x_draw, y_draw, color);
// error_step is p_i
int error_step;
if (Dx > Dy)
{
// init error_step with p_0
error_step = 2 * Dy - Dx;
while (x_draw != p2.X)
{
x_draw += x_increment;
if (error_step < 0)
{
error_step += 2 * Dy;
}
else
{
y_draw += y_increment;
error_step += 2 * Dy - 2 * Dx;
}
bitmap.SetPixel(x_draw, y_draw, color);
}
}
else
{
error_step = 2 * Dx - Dy;
while (y_draw != p2.Y)
{
if (error_step < 0)
{
error_step += 2 * Dx;
}
else
{
x_draw += x_increment;
error_step += 2 * Dx - 2 * Dy;
}
y_draw += y_increment;
bitmap.SetPixel(x_draw, y_draw, color);
}
}
}
