I am using FillPolygon with a semi-transparent color to draw a triangle (an arrow pointer). I have noticed that FillPolygon gives awkward results with an isocel triangle. One of the sides is overlapping DrawPolygon's side, while the two others aren't. I would have expected none or all, but not something in between.
Here's a sample: DrawPolygon uses a semi-transparent red, while FillPolygon uses a semi-transparent green. You can see one side is brown, the two other sides are red.
alt text http://www.slimcode.com/downloads/arrow.png
The coordinates for this example are: {X=36,Y=201}, {X=42,Y=207}, {X=30,Y=207}.
Using an opaque color would solve everything as I could call both DrawPolygon and FillPolygon, but I need to use a semi-transparent color. I'm drawing into an image if it can make a difference.
You want use a bitmap and do something like this. Note this is not runnable code.
Dim image As New Bitmap(<my_Xsize>, <my_Ysize>)
Dim gr As Graphics = Graphics.FromImage(image)
<Draw your FillPolygon>
<Erase the leftside of the polygon>
<Draw your Polygon>
gr.DrawImage(image, <myXcoor>, <myYcoor>)
By using a bitmap you can fiddle down to the pixel level to get the exact thing you want.
Hack: Draw the whole arrow as opaque in an intermediate buffer, then draw the whole buffer onto your image using the appropriate transparency.
Related
This is a work project. I inherited some code using SharpDX (a DirectX layer). One of my tasks is to fix a piece of code where certain image effects are applying to a geometric shape containing a fill. If the filter is applied to the fill itself, it doesn't conform to the edges. I've figured out the code to pull out an excerpt using the Geometry of the object. For various reasons, they want to keep the fill that exists outside of the shape (namely, we have some distortion effects that pull in pixels outside of the shape), so I need to overlay it over the background. The problem I'm running into is that I'm getting this single-pixel border...
Applying the Soft Edge filter to the visible part
The background with the shape cut out
The two composited together in the program
What I'm actually getting
I can't share a good bit of the code, due to parts of it being proprietary, but the mask is a byte array. I'm building it using the following code:
SingleChannelBitmap mask = new SingleChannelBitmap(MaxRequiredPixels.Width, MaxRequiredPixels.Height, 255);
mask.FillShape(new RectangleF(new PointF(0,0), mask.Size), this.Geometry, 0);
255 is the maximum Alpha value (transparent). I invert it to take the slice out of the background. The only thing I can think of is that, when I do the masking, it's not including the outer edge of the Geometry. I'm going to try expanding the mask by one pixel in the crudest way possible (basically, scanning through and taking anything which is 0 transparency and adding a 0 transparency pixel to the left, right, up, and down), but I know there has to be a more elegant solution.
This has to work for the 3D Edge bevel filter as well, so doing an arbitrarily large whitespace probably won't work for me either.
What you describe is essentially the same haloing problem that sometimes occurs with displaying PNG images. The PNG export process from several programs will store a solid color for any portions of the PNG that has zero alpha, instead of the actual color at those pixels. This makes them function similar to other image formats (GIF) which use a specific color to encode transparent pixels. This significantly reduces the size of the file, however, can cause issues when sampling the image.
Your situation is similar. Although the masked pixels have zero alpha, when doing bilinear sampling, you may sample in between pixels, mixing both color and alpha values (unless pixel and texel centers are perfectly aligned). For example, if you have a 100% alpha, white pixel, next to a 0% alpha red pixel, and sample in between both, the result will be a pink pixel at 50% alpha.
There are several possible solutions:
You could extend the borders of the color layer, such that the 0% alpha border has the same color as its non-0% alpha adjacent pixels.
Intentionally line up the pixel and texel centers, although this can be tricky and/or not possible, depending on your requirements (mostly dependent on resolution).
Use 'nearest' sampling, instead of bilinear when displaying the image. This way, you will never blend in a 0% alpha pixel. However, this may also not be desirable, because your image will likely exhibit more aliasing effects.
I'm able to fill a rectangle with an image and i apply a mask on top of the image using this code
args.DrawingSession.FillRectangle(rect, imgRnd, mask);
i need to apply some transform to this image, i'am able to do that with no issue, but i have encounter a strange issue, the last pixel is repeated.
i have used
imgRnd.ExtendX = CanvasEdgeBehavior.Wrap;
imgRnd.ExtendY = CanvasEdgeBehavior.Wrap;
and the image is repeated continuously.
My question is : there is a way to draw one time the image disabling and ExtendX and ExtendY?
FillRectangle will always fill all the pixels within the specified rectangle. The edge behavior enum controls what value they are filled with if the image is positioned such that it does not completely cover the rectangle being drawn.
How exactly are you transforming the image? Can you change that to also transform the rectangle itself, so you won't be trying to fill pixels that aren't covered by the image?
Another option is to use image effects (Microsoft.Graphics.Canvas.Effects namespace) which give much more detailed control than FillRectangle over how multiple images are transformed, combined, etc.
I have a C# capture application that captures screenshot of an application and draws it to another window. Now I would like to set one color (or range) of the screenshot to be transparent and then draw it like that.
I am drawing the screenshot as sprite to 3d (directx9) surface using SharpDX.
How can I do this transparency?
When converting your screenshot to a texture, your colors should be defined by four values R,G,B,A. Alpha channel is responsible for transparency, so you should check if a color has a value / range that you want to cut out and change it's alpha value to 0.
It was a bit odd situation. My alpha modified pictures did not show up when draw:ing.
It was because I did not specify alphablend mode in .Begin-statement.
And I did not find any other way to do it than going through the whole bitmap and changing the alpha value one pixel at the time.
There's a neat little library called YLScsDrawing that allows you to skew a bitmap between four corners, and then draw it. Unfortunately, whenever I attempt this, my rectangular bitmap always has incredibly aliased edges, even with IsBilinearInterpolation = True. How could I go about changing this library so that it antialiases the edges?
An example of what I mean can be found below. Look at the top of the green line.
I am processing images to change their color from black to red, blue, green etc based on the requirement. I use SetPixel methods to change color of each pixel of the image from black to say red.
It works mostly fine except the borders and some curves within the image. Let's say I've circled image filled with black color. Circled image color is changed but still when I zoom, I can see blackish dots around border which is not completely replaced with red color. I tried to dig around and found that it has something to do with anti-aliasing.
Has anything faced similar problem or have thoughts/suggestions on how to fix this issue?
Many thanks in advnace for your help!
Regards,
Tanush
It can be related with anti-aliasing. Anti-aliasing essence is that the more pixel is closer to the edge (boundary of something) the more pixel color is blended with background color (or we can say that it is more 'transparent').
So the problem may be that you need not only to replace source color to destination color, but also pixels which were blended from source color to background color.
To achieve this you need:
1) Run edge detection algorithm of some kind - it may be simple or advanced as you want.
2) If pixel is near edge and pixel is near other pixel of your source color, then calculate it's opacity (1-transparency) factor- which will be
opacity = (pixel_color-background_color)/(source_color-background_color)
3) Now calculate your color to which you must replace current anti-aliased pixel:
new_color = background_color * (1-opacity) + opacity * target_color
And put this new_color instead of antialiased pixel.
In summary:
You need to detect antialiased pixels and replace them with your version of antialiased pixels.
Hardest part of algorithm is detection of antialiased pixels - because you can't be sure that you found all edge pixels with 100% probability. Also you can't be sure was pixel antialiased or was just made initially of such color). Because of this you may get some color noise in final product. But in any case it should be better than just sit and wait :)
good luck