The System.Drawing.Graphics class has a property CompositionMode with two options: SourceOver (which, based on the alpha component, blends whatever is drawn with the background already existing) or SourceCopy which simply overwrites the background with whatever is being drawn.
Does something similar exist in WPF?
In WPF when i draw a PolyLine for example on top of another the new PolyLine always alphablends with the background. I think that is independent of the container being used. I am using a Canvas but could not find a blend mode property anywhere. What I want to do is what the SourceCopy compositionmode mentioned above does. I.e. the new PolyLine should simply overwrite whatever is already on the Canvas.
Is there a simple way to do that, short of using pixel shaders (which - as far as I understand - wouldn't work anyways because I don't have access to the Canvas backbuffer).
I am not stuck with a Canvas and would be happy to use any container that supports overwrite mode.
I currently have a solution based on a WriteableBitmap for which I obtain a System.Drawing.Graphics context and then manipulate the CompositionMode. It works but since my window is fullscreen that solution has serious performance impacts.
Clarification and example:
The WPF window is fully transparent and so is the Canvas (back ground color(0,0,0,0)). Now I draw a PolyLine with a Color.FromArgb(128,128,0,0). I now have a semi-transparent red polyline. Next I draw the same PolyLine with Color.FromArgb(0,0,0,0). The result is the same as before because of the alpha blending taking place. What I want, however, is that the red polyline is erased with the second polyline (which is exactly what the SourceCopy mode in the Graphics class does.
I think all you need to do is make sure that the brushes used to fill/stroke the PolyLine have fully opaque alpha values (i.e. 255). Then the background shouldn't be blended into it.
You could apply a Clipping Mask, this way you can provide the path to clip over the elements that are below it, but it might be tough to maintain after a lot elements are required to be clipped...
Related
I think I must be missing something obvious, but I'm unable to find this after several hours of searching. Is there no way to use a PictureBox or other control to contain an image with partial transparent/alpha-blended pixels, and place that over another image and have the blending be based on the image under it?
For example, this produces the results I want:
Place a panel on a form.
Add an OnPaint handler.
In the OnPaint handler draw 1 PNG, then draw another PNG over it, using Graphics.DrawImage for both.
This does not:
Place a PictureBox on a form and set it to a PNG.
Place another PictureBox on the form and set it to a PNG.
Place the 2nd picture box over the first.
...even if the 2nd picture box is just empty and has a background color of Transparent, it still covers the picture below it.
I've read this stems from all winform controls being windows, so by nature they aren't transparent.
...but even the 15 year old platform I'm migrating from, Borland's VCL, had several windowless controls, so it's hard to imaging winforms doesn't at least have some easy solution?
My first example above is one answer, true, but that adds a lot of work when you can only use one big panel and draw all of your "controls" inside of it. Much nicer if you can have separate controls with separate mouse events/etc. Even if not an image control, and a control I have to draw myself, that would be fine, as long as I can just put one image in each control. In VCL they called this a "paint box", just a rectangle area you could place on a form and draw whatever you want on it. Has it's own mouse events, Bounds, etc. If you don't draw anything in it, it is like it's not even there (100% transparent) other than the fact it still gets mouse events, so can be used as a "hot spot" or "target" as well.
The PictureBox control supports transparency well, just set its BackColor property to Transparent. Which will make the pixels of its Parent visible as the background.
The rub is that the designer won't let you make the 2nd picture box a child of the 1st one. All you need is a wee bit of code in the constructor to re-parent it. And give it a new Location since that is relative from the parent. Like this:
public Form1() {
InitializeComponent();
pictureBox1.Controls.Add(pictureBox2);
pictureBox2.Location = new Point(0, 0);
pictureBox2.BackColor = Color.Transparent;
}
Don't hesitate to use OnPaint() btw.
Sorry, I just found this... once I decided to Google for "winforms transparent panel" instead of the searches I was doing before, the TransPictureBox example show seems to do exactly what I need:
Transparency Problem by Overlapped PictureBox's at C#
Looks like there are 2 parts to it:
Set WS_EX_TRANSPARENT for the window style
Override the "draw background" method (or optionally could probably make the control style Opaque).
Say I have some grid that you need to scroll down to see all of its lines, and I'm interested in saving some lines that are not currently visible as a bitmap. Is it feasible, or do I have to actually scroll down, "take a snapshot", and then scroll up again?
This is a feasibility question, and thus I don't have code to share.
Yes. You can render any UIElement (and its children) to a writeable bitmap.
When you do that you also specify a transform. That means you can display any part of the UIElement (if you do not want it all).
Whether it is "visible" on screen is completely irrelevant to bitmap rendering. It does not work like a screen grab.
The output cropping is solely down to the size of the target bitmap and the render transform provided.
As an example Silverlight Rotate & Scale a bitmap image to fit within rectangle without cropping uses UIElements that are never part of the visual tree to create a bitmap that is then rendered.
Before drawing a shape on a canvas I have a preview that displays how the shape will look. I can adjust the opacity and then draw the shape. I may then wish to draw a second shape with a different opacity. My problem is that altering the opacity of the preview also alters the opacity of the shape that I have already drawn.
This has led me to believe that I need to create a copy of the brush used for the preview each time before drawing the shape.
There are various different brushes and for example, the gradient brushes require making a copy of the not just the gradient stop collection, but a new gradient stop for each gradient stop in the to-be-copied collection.
Am I down the right track here or should I be doing something else? Should I be copying or cloning? Would an extension method be the best way to go? Thoughts please.
What you need is cloning, it would be easy in wpf with XamlWriter/Reader, unfortunately you cannot do it in Silverlight. An extension method on Brush that makes a deep copy would work fine in your case though. You will have to handle the different brush type separately but it should not be an issue as there aren't that many.
I have a requirement to morph from an image (png) to a shape (polygon) in Silverlight 3 as an effect, but of course there is no built in transition or method to do this.
At the moment the best I have is fade one out and the other in, but can anyone suggest a decent alternative that may work or look better?
Regards
Moo
In Blend:
Create a rectangle. Set stroke to No Brush and Fill to Tile Brush.
For the ImageBrush of the Tile Brush, select your image.
In the object browser, select the rectangle, right click > Path > Convert to Path.
Use the pen tool to add some points to the path.
Add a storyboard.
Add a keyframe at 1 second. Blend will go into record mode
Use the direct selection tool to move the points into the polygon shape you want. Test out your animation.
At this point, the image morphs into a shape, but the image is still there. If you need to remove the image as well as morph it:
In your storyboard, at the keyframe at 1 second, change the opacity to 0.
Create a copy of the rectangle, but make sure fill is set to No Brush and Stroke is set to a color and width. Set the opacity to 0.
Add points, and mimic the animation you just set up for the image's rectangle.
Add a keyframe at 1 second for this element. In record mode, change the opacity to 100%.
The end result will be both paths morphing, the one with the image fading out while the one with no fill fading in.
I'm not a silverlight programmer, and don't know the details of what you want to do, so this is just a shot in the dark, but... if the shape you want the image to morph to is always going to have the same initial visual appearance (or some limited set of appearances) you might try morphing from the original image to an image of that shape, and then swapping the image that's the morph target for the geometry once you're done the morph. Course whether that would work or not is very dependent on the details of what you're doing. Sorry if you've already considered that and ruled it out.
You could possibly morph the image brush to the path of the shape by using an appropriate projection matrix. Or render a shape using the image brush and then morph that shape to the target shape, i.e. go from a rectangle to the target shape but using the image brush as the shape background. You may need to still warp the image brush somehow though.
An example of rendering a warped image is here in Charles Petzold's blog.
We are using the Mindfusion WPF Diagramming Component. I require a Visualbrush which must be able to be used in a third-party component for diagramming.
We have horizontally-stretching lanes on the diagramming canvas. We must define a background color for this lane, and some text on the top-left corner, to be repeated on the x-axis. The text must remain the same size while the rest of the lane is filled with color when the lane is re-sized.
Unfortunately, the only thing we can do is provide a Visualbrush to the diagramming component, which is then set as background for the lane. It seems impossible to work with this restriction because I am unable to define a text with fixed size, repeating on the x-axis, while also having a color brush stretching, all within a single Visualbrush. How can this be done?