Some questions about Textured material and ColorizedTexture material

[justinwhp]

Hi Experts,

I am trying to export SketchUp material. In the file …\SketchUpAPI\model\material.h, there is enum SUMaterialType with three material types.

/**
@enum SUMaterialType
@brief Indicates material type.
*/
enum SUMaterialType {
  SUMaterialType_Colored = 0,     ///< Colored material
  SUMaterialType_Textured,        ///< Textured material
  SUMaterialType_ColorizedTexture ///< Colored and textured material
};

For the material type “SUMaterialType_Textured”, we only assign a texture onto a face. However, we still get color information from the function “SUMaterialGetColor（）”. My question is what the color is? Is it calculated from the pixel of texture image file?

For the material type “SUMaterialType_ColorizedTexture”, we can assign a color and a texture onto a face. When calling the function “SUTextureWriteToFile()” to save the texture file, the color is also applied onto the image file. My question is: material has carried color information, why the color is applied to the image file during writing texture into disk file?

[xqtyler]

I have the same questions. Who can answer the question?

[DanRathbun]

A search of the developer categories on this subject:

• search: "colorize texture category:12"

… finds …

About colorized textures

SketchUp’s Ruby API bakes non-affine (quadrilateral) texture transformations and color modifications into the exported images. This is because many file formats and external applications might not support these features the same way as SketchUp does. There is unfortunately not much control over this. SketchUp supports two ways to adjust a material’s appearance, so-called colorize types: Colorization will turn all pixels monochrome in one single color tone with only variations in brightness. …

How does colorised texture work?

We should probably document this in a page in the documentation. Let start here in making the first attempt - let me know if you need more details. (EDIT: We now have documented it: GitHub - SketchUp/sketchup-colorize-algorithm: Explanation of SketchUp's colorization algorithm) SketchUp perform two types of color adjustments: If you set a material color for a textured material via the Ruby API’s Sketchup::Material.color= it sets the type to Sketchup::Material::COLORIZE_TINT. You can toggle…

[xqtyler]

Hi Dan,

For Colorized texture, I have no questions.

For the material type “SUMaterialType_Textured”, we only assign a texture onto a face. However, we still get color information from the function “SUMaterialGetColor（）”. The question is what the color is? Is it calculated from the pixel of texture image file?

Do you know what the color is for the material type “SUMaterialType_Textured”?

[xqtyler]

According to Ruby API document, the answer is yes. Please see the link:

Class: Sketchup::Material

I assume the C API should be the same.

[DanRathbun]

@xqtyler

The question is what the color is? Is it calculated from the pixel of texture image file?
Do you know what the color is for the material type “SUMaterialType_Textured”?

And the Ruby API doc says …

If it uses a Texture, this will return the average color.

So yes, there is some calculation going on.

@xqtyler

I assume the C API should be the same.

I can say that API “parity” is a public stated goal of the Extensibility Team of the SketchUp Development group.

In the thread I referenced (you should read it in it’s entirety,) Thomas gives pseudo code and refers to the Ruby API method …

• Sketchup::Texture#average_color()

He also talks about the C API lacking some functions in this regard back in September of 2017, just before the 2018 version came out.

But then in the "version.txt"of the C API SDK is listed a new function for ver 6 (2018,) released in November of 2017, we have listed …

• SUTextureGetAverageColor()

So it appears that it did make it into the 2018 C SDK release (C API ver 6.)

[xqtyler]

Hi Dan,

Thanks for your detailed explanation. I am using the 2018 C SDK release (C API ver 6). I have no question about the function SUTextureGetAverageColor().

My question is:
For the material type “SUMaterialType_Textured”, we only assign a texture onto a face. However, we still get color information from the function “SUMaterialGetColor(), not from SUTextureGetAverageColor()”. My question is what the color got from SUMaterialGetColor() is? Is it calculated from the pixel of texture image file?

Thanks

[bugra]

Hi,
I can’t see a reason for SUMaterialGetColor to return the average color for a textured-only material. Can you post a minimal code example that duplicates the issue?

[bugra]

I think I see what’s happening. When you set the texture on a material using SUMaterialSetTexture, the average texture color is applied to the material. So when you call SUMaterialGetColor, you get this average texture color back.

[tt_su]

@bugra

I think I see what’s happening. When you set the texture on a material using SUMaterialSetTexture, the average texture color is applied to the material. So when you call SUMaterialGetColor, you get this average texture color back.

Yup, you’ll also see the colour change in the UI.

[DanRathbun]

So the question that follows is, is this expected behavior or is it a bug ?

[xqtyler]

@bugra @DanRathbun and @tt_su Have any conclusion for the question “Is this expected behavior or is it a bug”?

[bugra]

I don’t believe this is a bug. You can see this behavior in SketchUp’s UI as well. If you apply a textured material to a surface and edit that in-model material, you’ll see that it assumes the average texture color. So even if you remove the texture (i.e. check off ‘Use texture image’), the material color will remain somewhat close to the texture color. At least that’s what I believe was the rationale.

[xqtyler]

Hi @bugra,

Thanks for your information. I agree with your point.
Maybe we can add some comments on the API SUMaterialGetColor() to tell SKP clients that what the color is when texture type is pure textured.

Thanks a lot again for your (@bugra @DanRathbun @tt_su) help. I have no questions about texture and materials.