在位图上绘制图形

Question

我尝试使用鼠标向上和鼠标向下在位图上绘制矩形。但问题是矩形总是延迟一个事件。例如，我尝试在第一次绘制一个矩形(0,0,50,50(，但在位图上没有矩形绘图。我继续画一个矩形(50,50,100,100(，但创建了一个矩形(0,0,50,50((不是矩形(50,50,100,100(。如果我继续绘制下一个矩形，它总是像那样延迟。请帮帮我！ 这是我的代码：

Rectangle rect = new Rectangle(0, 0, 0, 0);
int Xmouse;
int Ymouse;
public Form1()
{
InitializeComponent();
pictureBox1.Paint += new PaintEventHandler(pictureBox1_Paint);
this.DoubleBuffered = true;
}
private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
Xmouse = e.X;
Ymouse = e.Y;
drawOK = true;
}
private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
{
if (drawOK)
{
drawOK = false;
rect = new Rectangle(Xmouse * 3676 / 800, Ymouse * 3676 / 800, (e.X - Xmouse) * 3676 / 800, (e.Y - Ymouse) * 3676 / 800);
pictureBox1.Invalidate();
}
}

private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
using (var g = Graphics.FromImage(pictureBox1.Image))
{
using (Pen myPen = new Pen(Color.Black, 6))
{
g.DrawRectangle(myPen, rect);
}
}
}

Answer 1

尝试将绘制方法从 paint 之外移动到不同的 sub 中，然后从鼠标向上手动调用该 sub：

Rectangle rect = new Rectangle(0, 0, 0, 0);
int Xmouse;
int Ymouse;
bool drawOK;
private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
Xmouse = e.X;
Ymouse = e.Y;
Console.WriteLine("MouseDown({0},{1})", e.X, e.Y);
drawOK = true;
}
private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
{
if (drawOK)
{
drawOK = false;
Console.WriteLine("MouseUp({0},{1})", e.X, e.Y);
rect = new Rectangle(Xmouse , Ymouse , (e.X - Xmouse) , (e.Y - Ymouse) );
DrawRect();
pictureBox1.Invalidate();
}
}
private void DrawRect()
{
Console.WriteLine("drawing {0}", rect);
using (var g = Graphics.FromImage(pictureBox1.Image))
{
using (Pen myPen = new Pen(Color.Black, 6))
{
g.DrawRectangle(myPen, rect);
}
}
}
private void ClearPic()
{
using (var g = Graphics.FromImage(pictureBox1.Image))
{
using (Brush myPen = Brushes.White)
{
g.Clear(Color.White);                 
}
}
}
private void Form1_Load(object sender, EventArgs e)
{
Image bmp = new Bitmap(pictureBox1.Width, pictureBox1.Height);
pictureBox1.Image = bmp;
ClearPic();
pictureBox1.Paint += new PaintEventHandler(pictureBox1_Paint);
pictureBox1.MouseDown += pictureBox1_MouseDown;
pictureBox1.MouseUp += pictureBox1_MouseUp;
}