Unwanted Transparency Question

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Hi I have been writing a small "ribbon" like screensaver program using bezier curves.
It all works fine apart from a couple of colouring routines such as the snippet below.

d1,d2,d3,d4 represent the start, end and control points of the curve.
The formula calculates a couple of distance values and stores them in the xp/yp variables and these values are then used as rgb values.

Dim xp As Integer = Sqrt((d1.X - d4.X) ^ 2 + (d1.Y - d4.Y) ^ 2)
Dim yp As Integer = Sqrt((d2.X - d3.X) ^ 2 + (d2.Y - d3.Y) ^ 2)
mypen.Color = Color.FromArgb(1, xp Mod 255, yp Mod 255, xp + yp Mod 255)

Again the code works fine and produces some nice effects. However the Alpha value set to a value of 1 will cause the "shader" to produce a transparent colour occasionally. i.e the desktop or windows behind my black background will be shown inside the curves.

upping the alpha value cures the problem but causes washed out looking colours rather than the vibrant colours produced with a value of 1.

I have tried changing the forms transparency key and looking for rgb values that match the key then changing them to a near value instead but none of this seems to work. (I may have done something wrong here)

So anyone have any ideas?

[edit]
A picture to show the problem in action :

https://dl.dropboxusercontent.com/u/47121409/umm.jpg[

Posted 14-Sep-14 8:49am

5everin

Updated 14-Sep-14 9:05am

v4

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2 solutions

Solution 2

What else would you expect? The A value of 1 means very transparent color. Read this: "To create an opaque color, set alpha to 255":
http://msdn.microsoft.com/en-us/library/at1k42eh%28v=vs.110%29.aspx[^].

—SA

Posted 14-Sep-14 15:31pm

Sergey Alexandrovich Kryukov

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5everin 15-Sep-14 7:26am

I want transparent colours. I just want them on a black background, not "cutting" through it to reveal the desktop.

Sergey Alexandrovich Kryukov 15-Sep-14 10:31am

Then chose proper transparency... :-)
—SA

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5everin · Accepted Answer · 2014-09-14T10:36:00

Solution 1

Ok the penny suddenly dropped :)

Me.AllowTransparency = False

Though again this cures the problem. The program can also run in a transparent window over the desktop. So I thought a simple toggle of the boolean would do it. It seems not. First change is fine but then the program appears to ignore any further toggling.

have tried :

Me.AllowTransparency = Not Me.AllowTransparency
and if/then statements and both seem to do the same thing.

Still I guess my question is answered.

Posted 14-Sep-14 10:36am

5everin

Comments

Sergey Alexandrovich Kryukov 14-Sep-14 21:32pm

No, it is not answered. This property it totally irrelevant to ARGB transparency.
—SA

5everin 16-Sep-14 9:18am

I accept what you say. But it does cure the problem.

I think what is happening is that when the b' curves are drawn on top of previously drawn b' curves the blending that takes place sometimes results in a shade that matches the forms transparency key and the problem occurs. So its not something I can control without adding a ton of complexity and probably slowing down the program to the point of a slide show.