如何用for循环绘制正方形与三角形？能否点击顶点旋转三角形？

一、用For循环实现图形绘制 #

把图形的顶点坐标存入数组，通过循环遍历数组完成绘制，代码更简洁易维护：

1. 正方形绘制（For循环版） #

procedure squarClick(Sender: TObject);
var
  SquarePoints: array[0..3] of TPoint;
  i: Integer;
begin
  // 定义正方形四个顶点坐标
  SquarePoints[0] := Point(164, 182);
  SquarePoints[1] := Point(390, 118);
  SquarePoints[2] := Point(455, 345);
  SquarePoints[3] := Point(228, 408);

  // 设置画笔属性
  Canvas.Pen.Color := clGreen;
  Canvas.Pen.Style := psSolid;
  Canvas.Pen.Width := 1;

  // 移动到第一个顶点
  Canvas.MoveTo(SquarePoints[0].X, SquarePoints[0].Y);

  // 循环绘制各边
  for i := 1 to High(SquarePoints) do
  begin
    Canvas.LineTo(SquarePoints[i].X, SquarePoints[i].Y);
  end;

  // 闭合图形，回到起点
  Canvas.LineTo(SquarePoints[0].X, SquarePoints[0].Y);
end;

2. 三角形绘制（For循环版） #

procedure TRIANGLEClick(Sender: TObject);
var
  TrianglePoints: array[0..2] of TPoint;
  i: Integer;
begin
  // 定义三角形三个顶点坐标
  TrianglePoints[0] := Point(164, 182);
  TrianglePoints[1] := Point(453, 176);
  TrianglePoints[2] := Point(310, 428);

  // 设置画笔属性
  Canvas.Pen.Color := clRed;
  Canvas.Pen.Width := 1;

  // 移动到第一个顶点
  Canvas.MoveTo(TrianglePoints[0].X, TrianglePoints[0].Y);

  // 循环绘制各边
  for i := 1 to High(TrianglePoints) do
  begin
    Canvas.LineTo(TrianglePoints[i].X, TrianglePoints[i].Y);
  end;

  // 闭合图形
  Canvas.LineTo(TrianglePoints[0].X, TrianglePoints[0].Y);
end;

二、点击三角形顶点实现旋转操作 #

可以实现，步骤如下：

1. 定义全局状态变量 #

在窗体类中添加全局变量，存储三角形顶点、旋转中心和角度：

type
  TForm1 = class(TForm)
    PaintBox1: TPaintBox;
    TRIANGLEBtn: TButton;
    // 其他组件声明
  private
    TrianglePoints: array[0..2] of TPoint;
    RotateCenter: TPoint; // 旋转中心（点击的顶点）
    RotateAngle: Double; // 旋转角度（弧度制）
    function IsPointNearVertex(const P: TPoint; const Vertex: TPoint): Boolean;
  public
    { Public declarations }
  end;

2. 实现顶点点击判断函数 #

添加辅助函数，判断鼠标点击位置是否靠近顶点（容错范围10像素）：

function TForm1.IsPointNearVertex(const P: TPoint; const Vertex: TPoint): Boolean;
const
  Tolerance = 10;
begin
  Result := (Abs(P.X - Vertex.X) <= Tolerance) and (Abs(P.Y - Vertex.Y) <= Tolerance);
end;

3. 处理PaintBox点击事件 #

在OnMouseDown事件中识别点击的顶点，设置旋转参数并触发重绘：

procedure TForm1.PaintBox1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
  i: Integer;
begin
  if Button = mbLeft then
  begin
    for i := 0 to High(TrianglePoints) do
    begin
      if IsPointNearVertex(Point(X, Y), TrianglePoints[i]) then
      begin
        RotateCenter := TrianglePoints[i];
        RotateAngle := 30 * Pi / 180; // 每次顺时针转30度，转为弧度
        RotateTriangle();
        PaintBox1.Invalidate;
        Break;
      end;
    end;
  end;
end;

4. 实现旋转计算函数 #

用二维旋转公式计算旋转后的顶点坐标：

procedure TForm1.RotateTriangle;
var
  i: Integer;
  dx, dy: Double;
  newX, newY: Double;
begin
  for i := 0 to High(TrianglePoints) do
  begin
    // 计算顶点相对旋转中心的偏移量
    dx := TrianglePoints[i].X - RotateCenter.X;
    dy := TrianglePoints[i].Y - RotateCenter.Y;

    // 应用旋转公式
    newX := dx * Cos(RotateAngle) - dy * Sin(RotateAngle) + RotateCenter.X;
    newY := dx * Sin(RotateAngle) + dy * Cos(RotateAngle) + RotateCenter.Y;

    // 更新顶点坐标
    TrianglePoints[i] := Point(Round(newX), Round(newY));
  end;
end;

5. 修改绘制逻辑 #

更新三角形初始化和PaintBox绘制事件，使用全局顶点数组：

procedure TForm1.TRIANGLEClick(Sender: TObject);
begin
  // 初始化三角形顶点
  TrianglePoints[0] := Point(164, 182);
  TrianglePoints[1] := Point(453, 176);
  TrianglePoints[2] := Point(310, 428);
  PaintBox1.Invalidate;
end;

procedure TForm1.PaintBox1Paint(Sender: TObject);
var
  i: Integer;
begin
  // 绘制当前状态的三角形
  Canvas.Pen.Color := clRed;
  Canvas.Pen.Width := 1;
  Canvas.MoveTo(TrianglePoints[0].X, TrianglePoints[0].Y);
  for i := 1 to High(TrianglePoints) do
  begin
    Canvas.LineTo(TrianglePoints[i].X, TrianglePoints[i].Y);
  end;
  Canvas.LineTo(TrianglePoints[0].X, TrianglePoints[0].Y);
end;

现在点击三角形任意顶点，图形就会以该顶点为中心顺时针旋转30度。

内容的提问来源于stack exchange，提问作者Ebrahim