How to effectively draw on desktop in C#? - c#

I want to draw directly on the desktop in C#. From searching a bit, I ended up using a Graphics object from the Desktop HDC (null). Then, I painted normally using this Graphics object.
The problem is that my shapes get lost when any part of the screen is redrawn. I tried a While loop, but it actually ends up drawing as fast as the application can, which is not the update rate of the desktop.
Normally, I would need to put my drawing code in a "OnPaint" event, but such thing does not exist for the desktop.
How would I do it?
Example code: https://stackoverflow.com/questions/1536141/how-to-draw-directly-on-the-windows-desktop-c

I posted two solutions for a similar requirement here
Basically you have two options.
1- Get a graphics object for the desktop and start drawing to it. The problem is if you need to start clearing what you have previously drawn etc.
Point pt = Cursor.Position; // Get the mouse cursor in screen coordinates
using (Graphics g = Graphics.FromHwnd(IntPtr.Zero))
{
g.DrawEllipse(Pens.Black, pt.X - 10, pt.Y - 10, 20, 20);
}
2- The second option that I provide in the link above is to create a transparent top-most window and do all your drawing in that window. This basically provides a transparent overlay for the desktop which you can draw on. One possible downside to this, as I mention in the original answer, is that other windows which are also top-most and are created after your app starts will obscure your top most window. This can be solved if it is a problem though.
For option 2, making the form transparent is as simple as using a transparency key, this allows mouse clicks etc. to fall through to the underlying desktop.
BackColor = Color.LightGreen;
TransparencyKey = Color.LightGreen;

When you draw to HDC(NULL) you draw to the screen, in an unmanaged way. As you've discovered, as soon as windows refreshes that part of the screen, your changes are overwritten.
There are a couple of options, depending upon what you want to achieve:
create a borderless, possibly
non-rectangular window. (Use
SetWindowRgn to make a window
non-rectangular.) You can make this a child of the desktop window.
subclass the desktop window. This is not straightforward, and involves
injecting a DLL into the
Explorer.exe process.

To get an OnPaint for the desktop you would need to subclass the desktop window and use your drawing logic when it receives a WM_PAINT/WM_ERASEBKGND message.
As the thread you linked to says, you can only intercept messages sent to a window of an external process using a hook (SetWindowsHookEx from a DLL).
As mentioned a transparent window is another way to do it, or (depending on the update frequency) copying, drawing and setting a temporary wallpaper (as bginfo does).

This is difficult to do correctly.
It will be far easier, and more reliable, to make your own borderless form instead.

Related

Winform size and location of winform on screen regardless of resolution

I have a winform (c#, let's say 250px by 250px) that needs to stay in one location on the screen regardless of screen resolution i.e 800x600, 1920x1080 etc. The Winform itself contains only one element - a picturebox so what's inside really doesn't matter (no need to worry about fonts, etc.). I just need it to stick in one place on the screen from one monitor to another.
Any ideas? Thanks in advance.
Could you use one of these?
1) WindowsState = Maximized (then you dont worry, it always takes whole screen)
2) StartPosition = CenterScreen (then it always shows as centered), or CenterParent to center within parent form
3) Location = in this case you would have to do some math to get screen size, your form size than based on that center it but I dont see point of using this considering that StartPosition does it already for you.
Hope that helps
Ok, so in order to get the window at a fixed location given in % of the screen size, you need the screen size (e.g. using this answer), compute the desired position, and set it as the window-location.
Since you need to do it at startup, you could do it before you show the window, or maybe best inside a Frame.Loaded event handler.

Force external process to redraw borders after SetWindowPos

I am just trying to see if I can make a program that will sit along the left side of my monitor.
By doing so I am using a BackgroundWorker to loop through all of the users process (ones with a MainWindowTitle) and using SetWindowPos to move and resize them based upon my sidebar.
This all works fine except it causes the border to not draw (I guess that is a way to explain it).
I have attached 2 images and as you can see the borders don't seem to draw (and for Visual Studio it doesn't resize based upon the application BorderStyle)
This is the code I have so far:
foreach (Process p in Process.GetProcesses())
{
if (p.MainWindowTitle == "") continue;
if (p.MainWindowTitle.ToLower().Contains("studio"))
{
IntPtr i = p.MainWindowHandle;
RECT r;
GetWindowRect(i, out r);
if (r.Left <= -1608)
SetWindowPos(i, HWND.Top, Screen.AllScreens[1].Bounds.Left + 200, Screen.AllScreens[1].Bounds.Top, Screen.AllScreens[1].Bounds.Width - 200, Screen.AllScreens[1].Bounds.Height, SetWindowPosFlags.SWP_NOACTIVATE);
}
}
As you can see I am just trying to resize and reposition any (just Visual Studio at the moment) window on my second monitor (to the left of my first using a hackish kind of check :D)
I think you are misinterpreting what you see there: the borders do not draw, because (before you moved them) the windows where MAXIMIZED. Maximized windows typically don't have a border in Windows.
The solution is to first bring them back to normal state, before moving them to the desired coordinate, i.e.
ShowWindow(i, ShowWindowCommands.Normal);
That said, you'll still have to deal with multi-window processes and a myriad of fun little challenges. Enjoy the ride :-).

Full screen c# windows form covering all monitor

Is there a way to make make a windows form application full screen and black out your secondary monitors? So the main display is on your primary display and all your other monitors are just completely black?
You can use the Screen class which give you informations about the current active screens.
// Form myFrm
Rectangle r = new Rectangle();
foreach (Screen s in Screen.AllScreens)
{
if ( s != Screen.CurrentScreen ) // Blackout only the secondary screens
r = Rectangle.Union(r, s.Bounds);
}
myFrm.Top = r.Top;
myFrm.Left = r.Left;
myFrm.Width = r.Width;
myFrm.Height = r.Height;
myFrm.TopMost = true; // This will bring your window in front of all other windows including the taskbar
I can think of one way, and that would be to find out how many monitors there are on the computer, and their layout relative to each other, then create your primary window at 0,0, maximize it and set it to be TopMost, then do the same for the other displays, placing them at the screen locations corresponding to the top left of each monitor of the computer.
The only thing I can think of that would benefit from this in a WinForms environment is an app designed to give a test; the app would cover the entire desktop (except the taskbar; you'd have to disable the Start menu) and pretty much ensure that the user couldn't look at anything except the testing program. It will give you a minimal performance advantage.
Most of the apps that black out all the monitors except the main display are basically using DirectX to control the screen directly (through the lower-level interface to the graphics card). If you're using WinForms to make your program, you're about 50 levels of abstraction above using DirectX.
One way would be to create a second form in your application. One that, when given a set of dimensions, will open without border or menu and with the background set to black.
When your application runs, enumerate your monitors (count them to see how many) and find their dimensions. Your primary one will start at 0,0.
Then spawn a copy of that second form for each of your monitors (except your primary one) and give that form the dimensions of the monitor. They will then turn each screen black.
You will need to remember to keep a handle to each of the forms and terminate them when you terminate your main form.

Partial transparency with C# .NET 3.5 WinForms?

I'm making a .NET 3.5 app with a form that draws a partially transparent black background. I'm overriding OnPaintBackground to accomplish this:
protected override void OnPaintBackground( PaintEventArgs e )
{
using ( Brush brush = new SolidBrush( Color.FromArgb( 155, Color.Black ) ) )
{
e.Graphics.FillRectangle( brush, e.ClipRectangle );
}
}
It works, but occasionally the form draws over itself without clearing the screen, making the transparency darker than it should be. I've tried playing with Graphics.Flush() and Graphics.Clear(), but it either doesn't help or completely removes transparency. Any suggestions?
Edit:
Here's what it looks like, after starting the app on the left, and after the form redraws itself a few times (in response to tabbing from one control to another) on the right:
Transparency Issue http://www.quicksnapper.com/files/5085/17725729384A10347269148_m.png
Edit 2:
I was trying a few things out this morning and noticed that when the desktop behind the transparent portions change, it's not actually being redrawn. For example, if I open Task Manager and put it behind the window, you don't see it refreshing itself. This makes sense with what I've been seeing with the transparency levels. Is there a function to make Windows redraw the area behind your window?
Edit 3:
I've tried changing a few properties on the form, but they all result in the form drawing non-transparent black:
this.AllowTransparency = true;
this.DoubleBuffered = true;
this.Opacity = .99;
I'm going to try creating a separate window for the transparent portion as overslacked mentioned, but any other ideas are still welcome.
I think I would call this expected behavior, actually. What I would do is render my background to an in-memory bitmap and, in the paint event, copy that to the form (basic double-buffering).
If I'm way off base, could you post a screenshot? I don't know that I'm imagining what you're describing correctly.
EDIT:
I'm wondering about your use of OnPaintBackground... pre-.NET, if you were doing double-buffering you'd catch and ignore the WM_ERASKBKGND message (to prevent flicker), render your image to an offscreen buffer, and copy from the buffer to the screen on WM_PAINT. So, try changing from the OnPaintBackground to OnPaint.
I haven't done too much of this kind of thing in .NET, but I had a pretty good handle on it before; I just don't know if it'll translate well or not!
EDIT 2:
Marc, the more I think about what you're trying to do, the more problems appear. I was going to suggest creating a background thread dedicated to capturing the screen and rendering it darkened; however, in order to remove your own form you'd have to set the visibility to false which would create other problems....
If you're unwilling to give up, I would suggest creating two windows and "binding" them together. Create a semi-opaque window (by setting opacity) for your background window, and create a second "normal" window for the foreground. Use SetWindowRgn on the foreground window to cut away the background and position them on top of each other.
Good luck!
Is Graphics.CompositingMode set to CompositingMode.SourceCopy? That should cause painting the background twice to be equivalent to painting it once, since it will replace the existing alpha/color data instead of compositing over it.

Winforms: SuspendLayout/ResumeLayout is not enough?

I have a library of a few "custom controls". Essentially we have our own buttons, rounder corner panels, and a few groupboxes with some custom paint. Despite the "math" in the OnPaint methods, the controls are pretty standard. Most of the time, all we do is draw the rounded corners and add gradient to the background. We use GDI+ for all that.
These controls are ok (and very nice looking according to our customers), however and despite the DoubleBuffer, you can see some redrawing, especially when there are 20++ buttons (for example) on the same form. On form load you see the buttons drawing… which is annoying.
I'm pretty sure that our buttons are not the fastest thing on earth but my question is: if double buffer is "on", shouldn't all that redraw happen in background and the Windows subsystem should show the results "instantly" ?
On the other hand, if there's "complex" foreach loop that will create labels, add them to a panel (double buffered) and change their properties, if we suspendlayout of the panel before the loop and resume layout of the panel when the loop is over, shouldn't all these controls (labels and buttons) appear "almost instantly"? This doesn't happen like that, you can see the panel being filled.
Any idea why this is not happening? I know it's hard to evaluate without sample code but that's hard to replicate too. I could make a video with a camera, but trust me on this one, it's not fast :)
We've seen this problem too.
One way we've seen to "fix" it is to completely suspend drawing of the control until we're ready to go. To accomplish this, we send the WM_SETREDRAW message to the control:
// Note that WM_SetRedraw = 0XB
// Suspend drawing.
UnsafeSharedNativeMethods.SendMessage(handle, WindowMessages.WM_SETREDRAW, IntPtr.Zero, IntPtr.Zero);
...
// Resume drawing.
UnsafeSharedNativeMethods.SendMessage(handle, WindowMessages.WM_SETREDRAW, new IntPtr(1), IntPtr.Zero);
One of the things you should look at is whether you have set BackColor=Transparent on any of the child controls of your panels. The BackColor=Transparent will significantly degrade rendering performance especially if parent panels are using gradients.
Windows Forms does not use real transparency, rather it is uses "fake" one. Each child control paint call generates paint call on parent so parent can paint its background over which the child control paints its content so it appears transparent.
So if you have 50 child controls that will generate additional 50 paint calls on parent control for background painting. And since gradients are generally slower you will see performance degradation.
Hope this helps.
I'll approach your problem from a performance angle.
foreach loop that will create labels,
add them to a panel (double buffered)
and change their properties
If that's the order things are done, there's room for improvement. First create all your labels, change their properties, and when they are all ready, add them to the panel: Panel.Controls.AddRange(Control[])
Most of the time, all we do is draw
the rounded corners and add gradient
to the background
Are you doing the same thing over and over again? How are your gradients generated? Writing an image can't be that slow. I once had to create a 1680x1050 gradient in-memory, and it was really fast, like, too fast for Stopwatch, so drawing a gradient can't be so hard.
My advice would be to try and cache some stuff. Open Paint, draw your corners and save to disk, or generate an image in-memory just once. Then load (and resize) as needed. Same for the gradient.
Even if different buttons have different colors, but the same motif, you can create a bitmap with Paint or whatever and at runtime load it and multiply the Color values by another Color.
EDIT:
if we suspendlayout of the panel before the
loop and resume layout of the panel when the loop is over
That's not what SuspendLayout and ResumeLayout are for. They suspend the layout logic, that is, the automatic positioning of the controls. Most relevant with FlowLayoutPanel and TableLayoutPanel.
As for doublebuffering, I'm not sure it applies to custom draw code (haven't tried). I guess you should implement your own.
Doublebuffering in a nutshell:
It's very simple, a couple lines of code. On the paint event, render to a bitmap instead of rendering to the Graphics object, and then draw that bitmap to the Graphics object.
In addition to the DoubleBuffered property, also try adding this to your control's constructor:
SetStyle(ControlStyles.OptimizedDoubleBuffer |
ControlStyles.AllPaintingInWmPaint, true);
And if that ends up not being enough (which I'm gonna go out on a limb and say it isn't), consider having a look at my answer to this question and suspend/resume the redraw of the panel or Form. This would let your layout operations complete, then do all of the drawing once that's done.
You may want to look at the answer to my question, How do I suspend painting for a control and its children? for a better Suspend/Resume.
It sounds like what you are looking for is a "composited" display, where the entire application is drawn all at once, almost like one big bitmap. This is what happens with WPF applications, except the "chrome" surrounding the application (things like the title bar, resize handles and scrollbars).
Note that normally, unless you've messed with some of the window styles, each Windows Form control is responsible for painting itself. That is, every control gets a crack at the WM_ PAINT, WM_ NCPAINT, WM_ERASEBKGND, etc painting related messages and handles these message independently. What this means for you is that double buffering only applies to the single control you are dealing with. To get somewhat close to a clean, composited effect, you need to concern yourself not just with your custom controls that you are drawing, but also the container controls on which they are placed. For example, if you have a Form that contains a GroupBox which in turn contains a number of custom drawn buttons, each of these controls should have there DoubleBuffered property set to True. Note that this property is protected, so this means you either end up inheriting for the various controls (just to set the double buffering property) or you use reflection to set the protected property. Also, not all Windows Form controls respect the DoubleBuffered property, as internally some of them are just wrappers around the native "common" controls.
There is a way to set a composited flag if you are targeting Windows XP (and presumably later). There is the WS_ EX_ COMPOSITED window style. I have used it before to mix results. It doesn't work well with WPF/WinForm hybrid applications and also does not play well with the DataGridView control. If you go this route, be sure you do lots of testing on different machines because I've seen strange results. In the end, I abandoned used of this approach.
Maybe first draw on a control-only 'visible' (private) buffer and then render it:
In your control
BufferedGraphicsContext gfxManager;
BufferedGraphics gfxBuffer;
Graphics gfx;
A function to install graphics
private void InstallGFX(bool forceInstall)
{
if (forceInstall || gfxManager == null)
{
gfxManager = BufferedGraphicsManager.Current;
gfxBuffer = gfxManager.Allocate(this.CreateGraphics(), new Rectangle(0, 0, Width, Height));
gfx = gfxBuffer.Graphics;
}
}
In its paint method
protected override void OnPaint(PaintEventArgs e)
{
InstallGFX(false);
// .. use GFX to draw
gfxBuffer.Render(e.Graphics);
}
In its resize method
protected override void OnSizeChanged(EventArgs e)
{
base.OnSizeChanged(e);
InstallGFX(true); // To reallocate drawing space of new size
}
The code above has been somewhat tested.
I had the same problem with a tablelayoutpanel when switching usercontrols that I wanted displayed.
I completely got rid of the flicker by creating a class that inherited the table, then enabled doublebuffering.
using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
namespace myNameSpace.Forms.UserControls
{
public class TableLayoutPanelNoFlicker : TableLayoutPanel
{
public TableLayoutPanelNoFlicker()
{
this.DoubleBuffered = true;
}
}
}
I've had a lot of similar issues in the past, and the way I resolved it was to use a third-party UI suite (that is, DevExpress) rather than the standard Microsoft controls.
I started out using the Microsoft standard controls, but I found that I was constantly debugging issues which were caused by their controls. The problem is made worse by the fact that Microsoft generally does not fix any of the issues which are identified and they do very little to provide suitable workarounds.
I switched to DevExpress, and I have nothing but good things to say. The product is solid, they provide great support and documentation and yes they actually listen to their customers. Any time I had a question or an issue, I got a friendly response within 24 hours. In a couple of cases, I did find a bug and in both instances, they implemented a fix for the next service release.
I have seen bad winforms flicker on forms where the controls referred to a missing font.
This is probably not common, but it's worth looking into if you've tried everything else.

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