I've been making an application in C# which is designed to mimic the appearance and behavior of Windows' Snipping Tool application. Everything is fine, except the fact that double buffering (to stop the screen flickering) appears slow and laggy. It's not much lag, but it's enough to be noticeable especially when comparing the performance between my program and Snipping Tool. What else can I do to improve the performance and make it seem like there's no lag, like in Snipping Tool?
public Image Image { get; set; }
private Rectangle selection;
private Point startPoint;
public static Image Snip()
{
using (var bmp = new Bitmap(SystemInformation.VirtualScreen.Width, SystemInformation.VirtualScreen.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb))
{
using (var graphics = Graphics.FromImage(bmp)) graphics.CopyFromScreen(SystemInformation.VirtualScreen.Left, SystemInformation.VirtualScreen.Top, 0, 0, bmp.Size);
using (var snipper = new CaptureScreen(bmp, new Point(SystemInformation.VirtualScreen.Left, SystemInformation.VirtualScreen.Top)))
{
if (snipper.ShowDialog() == DialogResult.OK) return snipper.Image;
}
return null;
}
}
public CaptureScreen(Image screenShot, Point startPos)
{
InitializeComponent();
Cursor = Cursors.Cross;
BackgroundImage = screenShot;
ShowInTaskbar = false;
FormBorderStyle = FormBorderStyle.None;
StartPosition = FormStartPosition.Manual;
Size = screenShot.Size;
Location = startPos;
SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.DoubleBuffer, true);
}
protected override void OnMouseDown(MouseEventArgs e)
{
if (e.Button != MouseButtons.Left) return;
startPoint = e.Location;
selection = new Rectangle(e.Location, new Size(0, 0));
Invalidate();
}
protected override void OnMouseMove(MouseEventArgs e)
{
if (e.Button != MouseButtons.Left) return;
var x1 = Math.Min(e.X, startPoint.X);
var y1 = Math.Min(e.Y, startPoint.Y);
var x2 = Math.Max(e.X, startPoint.X);
var y2 = Math.Max(e.Y, startPoint.Y);
selection = new Rectangle(x1, y1, x2 - x1, y2 - y1);
Invalidate();
}
protected override void OnMouseUp(MouseEventArgs e)
{
if (selection.Width <= 0 || selection.Height <= 0) return;
Image = new Bitmap(selection.Width, selection.Height);
using (var gr = Graphics.FromImage(Image))
{
gr.DrawImage(BackgroundImage, new Rectangle(0, 0, Image.Width, Image.Height),
selection, GraphicsUnit.Pixel);
}
DialogResult = DialogResult.OK;
}
protected override void OnPaint(PaintEventArgs e)
{
using (var br = new SolidBrush(Color.FromArgb(127, Color.White)))
{
var x1 = selection.X;
var x2 = selection.X + selection.Width;
var y1 = selection.Y;
var y2 = selection.Y + selection.Height;
e.Graphics.FillRectangle(br, new Rectangle(0, 0, x1, Height));
e.Graphics.FillRectangle(br, new Rectangle(x2, 0, Width - x2, Height));
e.Graphics.FillRectangle(br, new Rectangle(x1, 0, x2 - x1, y1));
e.Graphics.FillRectangle(br, new Rectangle(x1, y2, x2 - x1, Height - y2));
}
using (var pen = new Pen(Color.Red, 1))
{
e.Graphics.DrawRectangle(pen, selection);
}
}
I think the reason it lags this way is because the application creates a screenshot and resizes the capture window to match the dimensions of all screens. I have a feeling this is what Snipping Tool does too, yet it still performs much faster.
Instead of using Invalidate() which will invalidate the entire painting area of your control each time you do a mousemove....and thus cause more painting work to be done...you can be more efficient by only invalidating the area that you need to change by using Invalidate() with a specified Rectangle.
When OnPaint is called...the e.ClipRectangle...equates to the "dirty" area that needs updating.....you can use that to optimize the painting work that you do in OnPaint.
You could also cache the creation of your Red Pen and White SolidBrush instead of creating them each time the OnPaint happened...you may or may not see any difference doing that.
Here's an update of your example:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace WindowsFormsApplication3
{
public partial class CaptureScreen : Form
{
public Image Image { get; set; }
private Rectangle selection;
private Rectangle previousselection;
private Point startPoint;
public static Image Snip()
{
using (var bmp = new Bitmap(SystemInformation.VirtualScreen.Width, SystemInformation.VirtualScreen.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb))
{
using (var graphics = Graphics.FromImage(bmp)) graphics.CopyFromScreen(SystemInformation.VirtualScreen.Left, SystemInformation.VirtualScreen.Top, 0, 0, bmp.Size);
using (var snipper = new CaptureScreen(bmp, new Point(SystemInformation.VirtualScreen.Left, SystemInformation.VirtualScreen.Top)))
{
if (snipper.ShowDialog() == DialogResult.OK) return snipper.Image;
}
return null;
}
}
public CaptureScreen(Image screenShot, Point startPos)
{
InitializeComponent();
Cursor = Cursors.Cross;
BackgroundImage = screenShot;
ShowInTaskbar = false;
FormBorderStyle = FormBorderStyle.None;
StartPosition = FormStartPosition.Manual;
Size = screenShot.Size;
Location = startPos;
SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.DoubleBuffer, true);
}
protected override void OnMouseDown(MouseEventArgs e)
{
if (e.Button != MouseButtons.Left) return;
startPoint = e.Location;
selection = new Rectangle(e.Location, new Size(0, 0));
previousselection = selection;
Invalidate();
}
protected override void OnMouseMove(MouseEventArgs e)
{
if (e.Button != MouseButtons.Left) return;
var x1 = Math.Min(e.X, startPoint.X);
var y1 = Math.Min(e.Y, startPoint.Y);
var x2 = Math.Max(e.X, startPoint.X);
var y2 = Math.Max(e.Y, startPoint.Y);
Invalidate(previousselection); // invalidate old rect area so it gets blanked out
previousselection = selection;
selection = new Rectangle(x1, y1, x2 - x1, y2 - y1);
Invalidate(selection); // invalidate new rect area so it gets drawn
}
protected override void OnMouseUp(MouseEventArgs e)
{
if (selection.Width <= 0 || selection.Height <= 0) return;
Image = new Bitmap(selection.Width, selection.Height);
using (var gr = Graphics.FromImage(Image))
{
gr.DrawImage(BackgroundImage, new Rectangle(0, 0, Image.Width, Image.Height),
selection, GraphicsUnit.Pixel);
}
DialogResult = DialogResult.OK;
}
protected override void OnPaint(PaintEventArgs e)
{
using (var br = new SolidBrush(Color.FromArgb(127, Color.White)))
using (var pen = new Pen(Color.Red, 1))
using (Region region = new Region(new Rectangle(0,0,Width,Height)))
{
region.Exclude(selection);
region.Intersect(e.ClipRectangle);
e.Graphics.FillRegion(br, region);
e.Graphics.DrawRectangle(pen, selection.X, selection.Y, selection.Width - 1, selection.Height - 1);
}
}
}
}