I have a strange problem. I made my own user control deriving from UserControl. I override OnPaint. Now I draw something in OnPaint. Let's say at position 0, 0.
If I call base.OnPaint after my custom drawing everything is fine. But if I call base.OnPaint before the stuff I'm drawing, it seems to ignore the containing control and the location is relative to the form instead of relative to the client area of the parent control. So when I draw at position (0, 0) it will effectively be drawn at negative x and y and I will only see a part of it. The base.OnPaint is UserControl.OnPaint. So I don't call my code there.
Here is an example:
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
var rect = new System.Drawing.Rectangle(this.ClientSize.Width - 16,
this.ClientSize.Height - 16, 16, 16);
e.Graphics.FillRectangle(new System.Drawing.SolidBrush(System.Drawing.Color.Red), rect);
//base.OnPaint(e);
}
In this case the red rectangle is displayed somewhere inside the client area but not at the lower right corner. If I uncomment the last line and comment the first line the red rectangle is displayed at the lower right corner as expected.
I don't get it. I did this many times and it always worked. So I tried to find any differences. The only I found is that I don't add my control in the designer but add it programmatically to another control with theContainingControl.Controls.Add(myMessedUpControl);.
This also happens for every parent-child-level I add. So if I create another control (another class) and also override OnPaint the behavior is the same if I add it to another user control.
Does anyone had this behavior before? How can I fix this? The problem is that I want to call base.OnPaint first and also everyone suggest this. But as I said I can't without messing the coordinates up.
One note: The coordinates are really 0, 0 in the debugger at the draw calls like DrawLine, DrawImage oder DrawString. But the result is displayed at negative coordinates (relative to the client area). It looks like the client coordinates are interpreted as client coordinates of the form. But I don't know why.
Found the problem
In my project there is a graphical overlay class which connects Paint event handlers to all controls in my form (the whole hierarchy). In this handler a transformation is performed. This graphical overlay kept me sleepless so many times. I guess I will remove it.
The Graphics object has a lot of mutable state. The order of operations matters if you mess with this mutable state - for example, you can use the Transform matrix to change the offset of everything rendered on the surface.
It sounds like your ascendant changes one of those during its own OnPaint handler without resetting it back. Try doing a e.Graphics.ResetTransform(); before you start your own painting. Make sure all the other state is also the way you want it (clip, DPI, ...).
Related
I'm making a graphics editor for my class project and i want to make so that when, for example a user loads a picture in to the editor or or draw something in the PictureBox, all the alpha parts are shown the chessboard like background.
My idea is that when I create a PictureBox with transparent background set, I create another one behind it, set its BackColor to white and add grey images 50x50, alternately horizontally and vertically. Is that a good approach to the problem? If, not do You have any suggestions?
In Photoshop, for example, I create image 1600x1600. When I zoom to a certain level, it shrinks the boxes and adds more of them to fill the image. If You'we used Photoshop of similar program you know what I mean. Now, how would I go about achieving the same effect?
Creating a Photoshop-like program is a fun project.
There will be many challenges along your way and it is well worth thinking ahead a little..
Here is a short and incomplete list of things to keep in mind:
Draw- and paint actions
Undo, redo, edit
Multiple layers
Zooming and scrolling
Saving and printing
So getting a checkerboard background is only the start of a long journey..
Using a PictureBox as the base canvas is a very good choice, as its several layers will help. Here is a piece of code that will provide you with a flexible checkerboard background, that will keep its size even when you scale the real graphics:
void setBackGround(PictureBox pb, int size, Color col)
{
if (size == 0 && pb.BackgroundImage != null)
{
pb.BackgroundImage.Dispose();
pb.BackgroundImage = null;
return;
}
Bitmap bmp = new Bitmap(size * 2, size * 2);
using (SolidBrush brush = new SolidBrush(col))
using (Graphics G = Graphics.FromImage(bmp) )
{
G.FillRectangle(brush, 0,0,size, size);
G.FillRectangle(brush, size,size, size, size);
}
pb.BackgroundImage = bmp;
pb.BackgroundImageLayout = ImageLayout.Tile;
}
Load an Image for testing and this is what you'll get, left normal, right zoomed in:
Yes, for saving this background should be removed; as you can see in the code, passing in a size = 0 will do that.
What next? Let me give you a few hints on how to approach the various tasks from above:
Scrolling: Picturebox can't scroll. Instead place it in a Panel with AutoScroll = true and make it as large as needed.
Zooming: Playing with its Size and the SizeMode will let you zoom in and out the Image without problems. The BackgroundImage will stay unscaled, just as it does in Photoshop. You will have to add some more code however to zoom in on the graphics you draw on top of the PB or on the layers. The key here is scaling the Graphics object using a Graphics.MultiplyTransform(Matrix).
Layers: Layers are imo the single most useful feature in PhotoShop (and other quality programs). They can be achieved by nesting transparent drawing canvases. Panels can be used, I prefer Labels. If each is sitting inside the one below it and the one at the bottom has the PB as its Parent, all their contents will be shown combined.
Don't use the Label directly but create a subclass to hold additional data and know-how!
Changing their order is not very hard, just keep the nested structure in mind and intact!
Hiding a layer is done by setting a flag and checking that flag in the painting actions
Other data can include a Name, Opacity, maybe an overlay color..
The layers should also be shown in a Layers Palette, best by creating a thumbnail and inserting a layer userobject in a FlowLayoutPanel
Draw Actions: These are always the key to any drawing in WinForms. When using the mouse to draw, each such activity creates an object of a DrawAction class you need to design, which holds all info needed to do the actual drawing, like:
Type (Rectangle, filledRectangle, Line, FreeHandLine (a series of Points), Text, etc.etc..)
Colors
Points
Widths
Text
The layer to draw on
maybe even a rotation
Along with the LayerCanvas class the DrawAction class will be the most important class in the project, so getting its design right is worth some work!
Only the topmost layer will receive the mouse events. So you need to keep track which layer is the active one and add the action to its actions list. Of course the active layer must also be indicated in the Layers Palette.
Since all drawing is stored in List(s), implementing a unlimited undo and redo is simple. To allow for effective drawing and undo, maybe a common action list and an individual list for each layer is the best design..
Undo and Redo are just matter of removing the last list element and pushing it onto a redo-stack.
Editing actions is also possible, including changing the parameters, moving them up or down the actions list or removing one from the middle of the list. It help to show an Actions Palette, like F9 in PhotoShop.
To flatten two or more layers together all you need is to combine their action lists.
To flatten all layers into the Image you only need to draw them not onto their canvas but into the Image. For the difference of drawing onto a control or into a Bitmap see here! Here we have the PictureBox.Image as the second level of a PB's structure above the Background.Image. (The 3rd is the Control surface, but with the multiple layers on top we don't really need it..)
Saving can be done by either by Image.Save() after flattening all Layers or after you have switched off the BackgroundImage by telling the PB to draw itself into a Bitmap ( control.DrawToBitmap() ) which you can then save.
Have fun!
This question is a little strange, but I'm going to try to explain everything as well as I can.
I've having trouble automating a specific occurrence of window repainting. Basically, I'm trying to to make the paint event fire as though the window had been moved while some of it's content was off-screen (because, for example, the window's dimensions are too large to fit on the screen).
I've tried using Invalidate(), Update() and Refresh(), as well as this.Invalidate(new Rectangle(0, 0, Width, Height));. however none produce the effects I'm expecting.
Currently, the case I'm testing for within the Paint event is when the PaintEventArgs ClipRectangle property has Width and Height greater both greater than zero. When the application is launched, and when all of the aforementioned methods are run, the subsequent PaintEventArgs ClipRectangle has all values of zero:
{ClipRectangle = {X=0,Y=0,Width=0,Height=0}}
However, when I manually drag the window (while some of it is off screen) and the paint event fires the ClipRectangle has these values:
{ClipRectangle = {X=0,Y=0,Width=1356,Height=1636}}
The shown Width and Height are the full dimensions of the window.
I'm assuming the difference in the two cases is that, in the latter, because some of the window is off-screen, all of it must be redrawn when moved to account for what was previously not on screen; though, admittedly, I'm not entirely sure of the exact cause of these different cases. Unfortunately, through all of my crazy, different attempts, my program only works when the Paint event is occurs in these specific circumstances. Is anyone aware of any way to force an event like this to occur (preferably regardless of whether the window is actually off-screen)? I don't care how hackey or weird a solution is as long as it works reliably.
Try adding this in the OnPaint function:
if (e.ClipRectangle.Width < 200 || e.ClipRectangle.Height<200)
{
this.Refresh();
}
else
{
//your paint code
}
I have a User Control with completely custom drawn graphics of many objects which draw themselves (called from OnPaint), with the background being a large bitmap. I have zoom and pan functionality built in, and all the coordinates for the objects which are drawn on the canvas are in bitmap coordinates.
Therefore if my user control is 1000 pixels wide, the bitmap is 1500 pixels wide, and I am zoomed at 200% zoom, then at any given time I would only be looking at 1/3 of the bitmap's width. And an object which has a rectangle starting at point 100,100 on the bitmap, would appear at point 200,200 on the screen provided you were scrolled to the far left.
Basically what I need to do is create an efficient way of redrawing only what needs to be redrawn. For example, if I move an object, I can add the old clip rectangle of that object to a region, and union the new clip rectangle of that object to that same region, then call Invalidate(region) to redraw those two areas.
However doing it this way means I have to constantly convert the objects bitmap coordinates into screen coordinates before supplying them to Invalidate. I have to always assume that the ClipRectangle in PaintEventArgs is in screen coordinates for when other windows invalidate mine.
Is there a way that I can make use of the Region.Transform and Region.Translate capabilities so that I do not need to convert from bitmap to screen coordinates? In a way that it won't interfere with receiving PaintEventArgs in screen coordinates? Should I be using multiple regions or is there a better way to do all this?
Sample code for what I'm doing now:
invalidateRegion.Union(BitmapToScreenRect(SelectedItem.ClipRectangle));
SelectedItem.UpdateEndPoint(endPoint);
invalidateRegion.Union(BitmapToScreenRect(SelectedItem.ClipRectangle));
this.Invalidate(invalidateRegion);
And in the OnPaint()...
protected override void OnPaint(PaintEventArgs e)
{
invalidateRegion.Union(e.ClipRectangle);
e.Graphics.SetClip(invalidateRegion, CombineMode.Union);
e.Graphics.Clear(SystemColors.AppWorkspace);
e.Graphics.TranslateTransform(AutoScrollPosition.X + CanvasBounds.X, AutoScrollPosition.Y + CanvasBounds.Y);
DrawCanvas(e.Graphics, _ratio);
e.Graphics.ResetTransform();
e.Graphics.ResetClip();
invalidateRegion.MakeEmpty();
}
Since a lot of people are viewing this question I will go ahead and answer it to the best of my current knowledge.
The Graphics class supplied with PaintEventArgs is always hard-clipped by the invalidation request. This is usually done by the operating system, but it can be done by your code.
You can't reset this clip or escape from these clip bounds, but you shouldn't need to. When painting, you generally shouldn't care about how it's being clipped unless you desperately need to maximize performance.
The graphics class uses a stack of containers to apply clipping and transformations. You can extend this stack yourself by using Graphics.BeginContainer and Graphics.EndContainer. Each time you begin a container, any changes you make to the Transform or the Clip are temporary and they are applied after any previous Transform or Clip which was configured before the BeginContainer. So essentially, when you get an OnPaint event it has already been clipped and you are in a new container so you can't see the clip (your Clip region or ClipRect will show as being infinite) and you can't break out of those clip bounds.
When the state of your visual objects change (for example, on mouse or keyboard events or reacting to data changes), it's normally fine to simply call Invalidate() which will repaint the entire control. Windows will call OnPaint during moments of low CPU usage. Each call to Invalidate() usually will not always correspond to an OnPaint event. Invalidate could be called multiple times before the next paint. So if 10 properties in your data model change all at once, you can safely call Invalidate 10 times on each property change and you'll likely only trigger a single OnPaint event.
I've noticed you should be careful with using Update() and Refresh(). These force a synchronous OnPaint immediately. They're useful for drawing during a single threaded operation (updating a progress bar perhaps), but using them at the wrong times could lead to excessive and unnecessary painting.
If you want to use clip rectangles to improve performance while repainting a scene, you need not keep track of an aggregated clip area yourself. Windows will do this for you. Just invalidate a rectangle or a region that requires invalidation and paint as normal. For example, if an object that you are painting is moved, each time you want to invalidate it's old bounds and it's new bounds, so that you repaint the background where it originally was in addition to painting it in its new location. You must also take into account pen stroke sizes, etc.
And as Hans Passant mentioned, always use 32bppPArgb as the bitmap format for high resolution images. Here's a code snippet on how to load an image as "high performance":
public static Bitmap GetHighPerformanceBitmap(Image original)
{
Bitmap bitmap;
bitmap = new Bitmap(original.Width, original.Height, PixelFormat.Format32bppPArgb);
bitmap.SetResolution(original.HorizontalResolution, original.VerticalResolution);
using (Graphics g = Graphics.FromImage(bitmap))
{
g.DrawImage(original, new Rectangle(new Point(0, 0), bitmap.Size), new Rectangle(new Point(0, 0), bitmap.Size), GraphicsUnit.Pixel);
}
return bitmap;
}
How would I draw something on a Canvas in C# for Windows Phone?
Okay, let me be a little more clear.
Say the user taps his finger down at 386,43 on the canvas. (the canvas is 768 by 480)
I would like my application to be able to respond by placing a red dot at 386,43 on the canvas.
I have no prior experience with Canvas whatsoever.
If this is too complex to be answered in one question (which it probably is), please give me links to other websites with Canvas and Drawing articles.
There are various ways of doing this. Depending on the nature of the red dot, you could make it a UserControl. For a basic circle, you can simply handle your canvas' ManipulationStarted event.
private void myCanvas_ManipulationStarted(object sender, ManipulationStartedEventArgs e)
{
Ellipse el = new Ellipse();
el.Width = 10;
el.Height = 10;
el.Fill = new SolidColorBrush(Colors.Red);
Canvas.SetLeft(el, e.ManipulationOrigin.X);
Canvas.SetTop(el, e.ManipulationOrigin.Y);
myCanvas.Children.Add(el);
}
I think you need to approach the problem differently. (I'm not including code on purpose, because of that).
Forms and controls in an Windows applications (including Phone) can be refreshed for several reasons, at any time. If you draw on a canvas in response to a touch action, you have an updated canvas until the next refresh. If a refresh occurs the canvas repaints itself, you end up with a blank canvas.
I have no idea what your end goal is, but you likely want to either keep track of what the user has done and store that state somewhere and show it in a canvas on the repaint of the canvas. This could be done with storing all the actions and "replaying" them on the canvas, or simply storing the view of the canvas as a bitmap and reload the canvas with that bitmap when refreshed. But, in the later case I think using a canvas isn't the right solution.
I've been working on a custom control and I've run into an issue with TextRenderer acting a bit surprisingly. In my OnPaint event I apply transform to the Graphics object to compensate for the scroll position like this:
e.Graphics.Transform = new System.Drawing.Drawing2D.Matrix(1, 0, 0, 1, this.AutoScrollPosition.X, this.AutoScrollPosition.Y);
Then I pass the graphic object to all sub elements of the control so that they paint themselves onto it. One of this elements should draw text string onto the graphics surface. And this is where I've got an issue. This line seems to work correctly when scrolling:
e.Graphics.DrawString(this.Text, this.Font, brush, new PointF(this.Rectangle.X, this.Rectangle.Y));
But when I use TextRenderer I get a completely different result. Heres the text line that supposed to draw the text:
TextRenderer.DrawText(e.Graphics, this.Text, this.Font, this.Rectangle, this.TextColor, TextFormatFlags.PreserveGraphicsClipping | TextFormatFlags.PreserveGraphicsTranslateTransform);
I thought that these two lines should produce the same result. But for some reason the second one applies the graphics transform differently and as a result, when I scroll the control all the text lines move around with different speed than the rest of the elements on the drawing surface. Could someone explain me why this is happening?
Here's my best guess at this: TextRenderer.DrawText is GDI-based and therefore resolution-dependant. Graphics.DrawString is GDI+ and therefore resolution-independant. See also this article.
Since you say that the texts "move around with different speed", probably what happens is that the GDI call uses a different "default" resolution than the one your Graphics object has. That'd mean that you'd have to adjust your AutoScrollCoordinates to respect the difference between your Graphics object resolution and the "default" GDI resolution.