Opacity of preview color in C# component

I'm having trouble with setting the color of a Brep in my C# component. The command FromArgb() takes four arguments which represents alpha, red, green, and blue. As I understand the first argument alpha, which can vary between 1 and 255, corresponds to the opacity of the previewed Brep (255 being solid and 1 being transparant). With my code below I manage to change the color but not the opacity. Changing int a below doesn't give any effect. The previewed Brep is always displayed as solid (255) no matter of the value of int a. Changing int r, g and b however gives effect on the previewed color. It is like the first argument doesn't have any effect.

Any Ideas??

int a = 180; // Opacity??
int r = 10; // red
int g = 10; // green
int b = 10; // blue

brep = nb;
alpha = a;
red = r;
green = g;
blue = b;

}

// <Custom additional code>
Brep brep;
int alpha;
int red;
int green;
int blue;

public override void DrawViewportMeshes(IGH_PreviewArgs args)
{
args.Display.DrawBrepShaded(brep, new Rhino.Display.DisplayMaterial(System.Drawing.Color.FromArgb(alpha, red, green, blue)));
}
// </Custom additional code>
}

Replies to This Discussion

Permalink Reply by David Rutten on October 10, 2013 at 10:37am

Hi Benjamin,

alpha values can vary between 0 and 255, where 0 is indeed fully transparent.

A Rhino Display material however doesn't support colours with transparency. The .NET color type (which does support an alpha channel) is converted into a Rhino colour type and the alpha information is discarded. Instead, you have to modify the Transparency property of the DisplayMaterial. This property is completely separate from the Diffuse colour.

David Rutten

david@mcneel.com

Tirol, Austria

Permalink Reply by Benjamin on October 10, 2013 at 10:46am

Hi David,

I see, I'm kind of a beginner in C#, can you write an example of how to modify the Transparency property of the DisplayMaterial?

// Benjamin

Permalink Reply by Giulio Piacentino on October 10, 2013 at 11:43am

Hi Benjamin,

There should be another constructor available that allows to use a double for the transparency. You should be able to use it like so (this being a very long line):

args.Display.DrawBrepShaded(brep, new Rhino.Display.DisplayMaterial(System.Drawing.Color.FromArgb(red, green, blue), doublePrecisionAlpha));

DisplayMaterial Line 53...

Transparency goes from 0.0-1.0: github.com...

This is the way you can set it via the property:

Rhino.Display.DisplayMaterial material = new Rhino.Display.DisplayMaterial(System.Drawing.Color.FromArgb(red, green, blue), doublePrecisionAlpha);

material.Transparency = 0.5;

args.Display.DrawBrepShaded(brep, material);

You can get this type of information in a C# book.

I hope this helps,

Giulio

Giulio Piacentino
for Robert McNeel & Associates
giulio@mcneel.com

Permalink Reply by Benjamin on October 11, 2013 at 8:16am

Thanks a lot! Works great :)

Permalink Reply by Benjamin on October 12, 2013 at 5:03am

Another question on the same topic:

In the same component I have a list of Point3d as output. These points will by default be previewed as red crosses, is there any way to overwrite the preview of them and make them invisible?

Permalink Reply by David Rutten on October 12, 2013 at 11:48am

You can switch the preview off for an output parameter. This is easiest inside the RegisterOutputParams() function. You can call pManager.HideParameter(1) for example.

You can enable/disable the preview of any input/output parameter at any time, but you'll have to cast the IGH_Param to IGH_PreviewObject before you get access to the Hidden property.

David Rutten

david@mcneel.com

München, Germany

Permalink Reply by Benjamin on October 14, 2013 at 4:26am

Can't get it to work, can anyone take a look?

public override void RegisterOutputParams(IGH_PreviewObject pManager)
{
pManager.HideParameter(1);
}

Permalink Reply by David Rutten on October 14, 2013 at 6:07am

That method doesn't register any output parameters... Can you please post your entire method?

David Rutten

david@mcneel.com

Seattle, WA

Permalink Reply by Benjamin on October 14, 2013 at 6:24am

TopColumn1 = TP1; // List<Point3d>
TopColumn2 = TP2; // List<Point3d>
SecondaryBeam = TPS; // List<Point3d>

brep = nb;
alpha = a;
red = r;
green = g;
blue = b;
}

// <Custom additional code>
Brep brep;
double alpha;
int red;
int green;
int blue;

public override void RegisterOutputParams(IGH_PreviewObject pManager)
{
pManager.HideParameter(1);
}

public override void DrawViewportMeshes(IGH_PreviewArgs args)
{
args.Display.DrawBrepShaded(brep, new Rhino.Display.DisplayMaterial(System.Drawing.Color.FromArgb(red, green, blue), alpha));
}
// </Custom additional code>
}

Permalink Reply by David Rutten on October 14, 2013 at 10:45am

It's still empty:

public override void RegisterOutputParams(IGH_PreviewObject pManager)
{
pManager.HideParameter(1);
}

If you're not adding any outputs, then you also cannot hide any outputs.

David Rutten

david@mcneel.com

Seattle, WA

Permalink Reply by Benjamin on October 14, 2013 at 1:17pm

I still can't figure out how to write the code. Could you maybe write an example? I'm sorry but I'm not very experienced in writing in C#.

Permalink Reply by David Rutten on October 14, 2013 at 7:21pm

public override void RegisterOutputParams(IGH_PreviewObject pManager)
{

pManager.AddBrepParameter("Brep", "B", "Shape");

pManager.AddPointParameter("Pt", "P", "Point");
pManager.HideParameter(1);
}

(For the sake of brevity I didn't include the access argument)

The HideParameter(index) method will switch the preview off for the parameter at the given index. In this case the point parameter.

David Rutten

david@mcneel.com

Seattle, WA