Color interpolation across a face

ArunYoganandan

Hello all,

Is there a way to set up the color for each vertex in a face and let the color of the face be the interpolated value?

This is a pretty common thing in openGL. For eg. in OpenGL, you could set the color array to

float[] colors = { 
                1f, 0f, 0f, 1f, // vertex 0 red
                0f, 1f, 0f, 1f, // vertex 1 green
                0f, 0f, 1f, 1f, // vertex 2 blue
                1f, 0f, 1f, 1f, // vertex 3 magenta
        };

across a square and you would get an image like
http://blog.uncle.se/wp-content/uploads/2012/02/02_SmoothColoring.png

Is there a way to do something like that programmatically in Sketchup? I'm only able find ways to set the color of the whole face.

Thanks in advance.
Arun

Dan Rathbun

You might use THAT image as a material's texture applied to the face. Then adjust the corners of the material image to the face's vertices. ??

Dan Rathbun

If you are thinking of creating the images "on-the-fly" then you'll need to use a 3rd party Library, such as ImageMajik etc. SketchUp does use PaintLib internally, but I do not know of anyone accessing it.

ArunYoganandan

@dan rathbun said:

You might use THAT image as a material applied to the face. Then adjust the corners of the material image to the face's vertices. ??

Hi Dan,

Thanks for your reply. What I'm trying to do is build a sliceable color cube like
http://www.sonycsl.co.jp/person/nielsen/visualcomputing/programs/colorcube-1.png
This is an immersive system and the user would be able to grab a corner and move it within the original cube's dimensions in 3D to
indicate the color desired. i.e, position 0.4,0.1,0.3 within the cube will denote the corresponding RGB values.
When the corner is moved, the faces will also correspondingly change in shape/fragment (Exactly like how it would behave when the vertex of a cube is moved in sketchup)
revealing new colors at the depth (like slicing a volume with interpolated colors).

Simply put, the faces of the cube get modified to different configurations and hence I will not be able to use a static texture. Something like a GLSL shader would be perfect except I don't think we could do that in SU?

Thanks,
Arun

Dan Rathbun

If you know the binary fileformat for some image filetype, you could write out a file in binary mode:

` img = File.open('myimage.bmp',"wb")

img.write(value)

...

img.close`

Then bring that image into your materials collection.

Dan Rathbun

Hmmm.. I'll need to think on that...

Have you been following what Aerilius' OnScreen GUI Toolkit

or: Chris Fullmer's On Screen GUI RGB Colorpicker

Dan Rathbun

To draw in OpenGL style (either 3D or 2D,) in SketchUp, must be done within a Tool class, using the View instance's family of draw methods.

see:
https://developers.google.com/sketchup/docs/ourdoc/view#draw

Dan Rathbun

So.. for color interpolation within a Tool class, when you set the color (just prior to painting a point,) with view.drawing_color=() you would evaluate the argument using color.blend

The receiver color would be color of one vertice, arg1 the other vertice's color, and the weight arg would be percentage ( Float) of the distance between the two vertices.

thomthom

The API doesn't let you set vertex colour. Wish it did.

Dan Rathbun

That's not what he wants.

He wants to draw multi-gradient color fill, on-the-fly.

thomthom

@dan rathbun said:

That's not what he wants.

He wants to draw multi-gradient color fill, on-the-fly.

Yes - and in OpenGL you do that by defining a colour for each vertex in a polygon where the shader then creates a gradient between each vertex colour across the polygon surface.

Dan Rathbun

Yep.. it would be nice to have more OpenGL draw functions.
Implementing a shader in Ruby is bound to be slow.

Aerilius

@dan rathbun said:

... you would evaluate the argument using color.blend

color.blend makes brown out of red and green.
In case you need a different interpolation (where you want red and green to result yellow), you need to write your own interpolation method, or take Color.interpolate(color1, color2,...) of https://bitbucket.org/Aerilius/color/wiki/Home

ArunYoganandan

Thanks everyone for the replies.

@Dan using the draw in a tool's view method looks like a plausible option. Let me dig into it and get back.

Thanks again.