x,y lines following mouse

[sagey]

i'm using a selection rectangle to select an area. to make it easier to select the area i make the cursor a crosshair.

what i would really like to do is for there to be four lines that follow the mouse cursor

               y line
                  |
                  |                   
x Line            |
------------ --  -- -------------------
                  |
                  |
                  |

that way the user can easily see the area he is about to select before he selects it.

I'm not really sure how to do this. i can get the x,y location of the mouse easy enough.

and i guess i'd have to use the mousemove event to constantly re-get the x,y position.

but i'm not sure how to go about drawing the lines, and putting the rest of it together.

any pointers would be gratefully received

[sagey]

that diagram doesn't reflect what i mant to represent. it was meant to be a cross hair with an x and y line.

sorry

[PT Exorcist]

What you want to do is very easy to do it I understood it well...you'll just have to put in the MouseMove event it to draw a vertical line and a horizontal line:

the vertical line:
point A(
mouse X's cordinate,
0)

point B(
mouse X's cordenate,
picture's height)

the horizontal line:
point A(
mouse y's cordinate,
0)

point B(
mouse y's cordinate,
width)

Hope i was clear enough

[CornedBee]

You have to erase the old line, too.

[sagey]

i've wrriten some basic code like this:

the drawline bits are correct, but i'm not sure how to use this method with the mousemove method and the paint event.

i guess every time there is a mousemove event i need to call the method below (or something like it)
but i'm not sure how to do it.

		public void DrawLineFloat(PaintEventArgs pe)
		{
			// Create pen.
			Pen blackPen = new Pen(Color.FromArgb(128,0,0,255), 1);
			// Create coordinates of points that define line.
			float formLeft = this.Left;
			float formTop = this.Top ;
			float formRight = this.Right ;
			float formBottom = this.Bottom ;
			// Draw line to screen.
			pe.Graphics.DrawLine(blackPen,0,mouseY,mouseX,mouseY );
			pe.Graphics.DrawLine(blackPen, mouseX, 0, mouseX,mouseY);
			pe.Graphics.DrawLine(blackPen, formRight, mouseY, mouseX, mouseY);
			pe.Graphics.DrawLine(blackPen, mouseX, formBottom,mouseX, mouseY);
		}

I did muck around with using the form.refresh method, but that just meant the whole form being andreloaded (i open an image in the onpaint handler) and was crap.

[CornedBee]

You can't use PaintEvent here. Put the code in the mousemove handler and obtain a Graphics differently, I think Form has a method to do that.

[sagey]

yeah thats sort of my question.

i'd thought of putting the code in the mousemove, but i'm unsure how to obtain a graphics object etc so i can do the drawline.

i feel like i'm being really stupid.

[CornedBee]

That's what a reference is for

Form.CreateGraphics

[sagey]

Cheers, thats the ****er i was after. got it working of sorts. now just need to delete the existing line on every mousemove

			Pen blackPen = new Pen(Color.FromArgb(128,0,0,255), 1);
			Graphics g = SelectionRectangle.ActiveForm.CreateGraphics();
			// Create coordinates of points that define line.
			float formLeft = this.Left;
			float formTop = this.Top ;
			float formRight = this.Right ;
			float formBottom = this.Bottom ;
			mouseX = e.X ;
			mouseY = e.Y ;
			// Draw line to screen.
			g.DrawLine(blackPen,0,mouseY,mouseX,mouseY );
			g.DrawLine(blackPen, mouseX, 0, mouseX,mouseY);
			g.DrawLine(blackPen, formRight, mouseY, mouseX, mouseY);
			g.DrawLine(blackPen, mouseX, formBottom,mouseX, mouseY);

[PT Exorcist]

From what I've read in the forums pictures seem to have 2 properties, in the back one you can put the image and in the other you can draw your lines. That way you just delete the upper one and draw the lines

[CornedBee]

I recommend using the invert ROP2 mode (R2_NOT in plain API) to draw the line and erase it again.

[Magiaus]

I'm suprised there isn't a provided class for drawing BoundingBoxes like that....

this code doesn't work but it's has an interesting effect...

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace BoundingBox
{
	/// <summary>
	/// Summary description for Form1.
	/// </summary>
	public class Form1 : System.Windows.Forms.Form
	{
		/// <summary>
		/// Required designer variable.
		/// </summary>
		private System.ComponentModel.Container components = null;

		public Form1()
		{
			//
			// Required for Windows Form Designer support
			//
			InitializeComponent();

			//
			// TODO: Add any constructor code after InitializeComponent call
			//
		}

		/// <summary>
		/// Clean up any resources being used.
		/// </summary>
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (components != null) 
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Windows Form Designer generated code
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{
			// 
			// Form1
			// 
			this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
			this.ClientSize = new System.Drawing.Size(484, 505);
			this.Cursor = System.Windows.Forms.Cursors.Cross;
			this.Name = "Form1";
			this.Text = "Form1";
			this.MouseDown += new System.Windows.Forms.MouseEventHandler(this.Form1_MouseDown);
			this.MouseUp += new System.Windows.Forms.MouseEventHandler(this.Form1_MouseUp);
			this.MouseMove += new System.Windows.Forms.MouseEventHandler(this.Form1_MouseMove);

		}
		#endregion

		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main() 
		{
			Application.Run(new Form1());
		}
		private bool isMouseDown = false;
		private System.Drawing.Drawing2D.GraphicsState orgState = null;
		private System.Drawing.Drawing2D.GraphicsState oldState = null;
		private PointF origanPoint;

		private void Form1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			Graphics g = this.CreateGraphics();
			if(orgState != null)
			{	
				g.Restore(orgState);
				g.Flush();
				orgState = null;
				oldState = null;
			}
			isMouseDown = true;
			orgState = g.Save();
			oldState = g.Save();
			origanPoint = new PointF(e.X, e.Y);
		}

		private void Form1_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			isMouseDown = false;
		}

		private void Form1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			if(isMouseDown)
			{
				Graphics g = this.CreateGraphics();
				g.Restore(oldState);
				g.Flush();
				g.DrawRectangle(System.Drawing.Pens.Black,origanPoint.X,origanPoint.Y,(e.X - origanPoint.X),(e.Y - origanPoint.Y));
				oldState = g.Save();
			}
		}
	}
}

[Magiaus]

well drop this in an empty form name Form1 and you got a box drawing machine. not the best though because it will erase stuff that might not need to be erased...... in the old days i would have back buffered an image of the form or ctl but now thats to much stuff to figure out cause I haven't used the drawing namespace much.....

		private bool isMouseDown = false;
		private PointF origanPoint;

		private void Form1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			//Graphics g = this.CreateGraphics();
			isMouseDown = true;
			origanPoint = new PointF(e.X, e.Y);
		}

		private void Form1_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			isMouseDown = false;
		}

		private void Form1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			if(isMouseDown)
			{
				Graphics g = this.CreateGraphics();
				g.Clear(this.BackColor);
				g.DrawRectangle(System.Drawing.Pens.Black,origanPoint.X,origanPoint.Y,(e.X - origanPoint.X),(e.Y - origanPoint.Y));
			}
		}