# Ruby script for Texture positioning **URL:** \ **Category:** Ruby API\ **Created:** [April 7, 2025, 7:35pm UTC](https://forums.sketchup.com/t/ruby-script-for-texture-positioning/322437 "2025-04-07T19:35:42Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![evgeny27](https://sea2.discourse-cdn.com/sketchup/user_avatar/forums.sketchup.com/evgeny27/32/243558_2.png) [@evgeny27](https://forums.sketchup.com/u/evgeny27)\ **Post date:** [April 7, 2025, 7:35pm UTC](https://forums.sketchup.com/t/ruby-script-for-texture-positioning/322437/1 "2025-04-07T19:35:42Z")
Hey everyone, I’m trying to write a simple Ruby script that does the following: - Takes a material named `"TestTexture"` from the model - Applies it to a face I select - Aligns and stretches the texture so it fits **exactly** to the face’s **bounding rectangle** - Starts from the lower-left corner, aligned with the face orientation * * * ### What I’ve already tried: - Using `face.position_material(material, pt0, pt1, pt2)` with 3 valid `Point3d` - Ensuring the points are **not collinear** , and lie **within the face plane** - Using clean bounding box points (`face.bounds.min`) and offsetting by axes - Also tried projecting from face center using `face.normal`, `xaxis`, `yaxis` - Even tried using 8-argument version of `position_material` (with UVs) — which isn’t supported - Attempted to work with `face.uv_set` — turns out not exposed in Ruby API - Also tried using `UVHelper` to assist with coordinate mapping No matter what I try, `position_material` almost always throws this error: ```auto ArgumentError: Cannot convert argument to Geom::Vector3d ``` Any ideas or sample code would be a huge help 🙏 Thanks in advance! ---
**Author:** ![DanRathbun](https://sea2.discourse-cdn.com/sketchup/user_avatar/forums.sketchup.com/danrathbun/32/500_2.png) [@DanRathbun](https://forums.sketchup.com/u/DanRathbun)\ **Post date:** [April 7, 2025, 8:12pm UTC](https://forums.sketchup.com/t/ruby-script-for-texture-positioning/322437/2 "2025-04-07T20:12:17Z")
> [@evgeny27](#): > > Starts from the lower-left corner, aligned with the face orientation I believe that the UV coordinates start from the top left corner. In my testing it appears that the documentation is lacking. The UV coordinates in `face.position_material` are scale factors between `0.0` and `1,0`. See these other topics: - [Generate clickable images and assign functions to it](https://forums.sketchup.com/t/generate-clickable-images-and-assign-functions-to-it/264192) - [How to rotate a texure following the bigger face side?](https://forums.sketchup.com/t/how-to-rotate-a-texure-following-the-bigger-face-side/314749/) > [@evgeny27](#): > > Even tried using 8-argument version of `position_material` (with UVs) — which isn’t supported It isn’t? … Is an exception raised? > [@evgeny27](#): > > No matter what I try, `position_material` almost always throws this error: > > ```auto > ArgumentError: Cannot convert argument to Geom::Vector3d > > ``` We cannot help much without a test model file and a minimal test script demonstrating the issue." ---
**Author:** ![evgeny27](https://sea2.discourse-cdn.com/sketchup/user_avatar/forums.sketchup.com/evgeny27/32/243558_2.png) [@evgeny27](https://forums.sketchup.com/u/evgeny27)\ **Post date:** [April 9, 2025, 7:41pm UTC](https://forums.sketchup.com/t/ruby-script-for-texture-positioning/322437/3 "2025-04-09T19:41:38Z")
> [@DanRathbun](#): > > I believe that the UV coordinates start from the top left corner. > > In my testing it appears that the documentation is lacking. The UV coordinates in `face.position_material` are scale factors between `0.0` and `1,0`. OMG! After years of positioning textures manually (where the red pin always marked the origin at the lower-left corner), I never even considered that position\_material’s UV mapping starts from the top-left. Thank you for pointing that out! ---
**Author:** ![DanRathbun](https://sea2.discourse-cdn.com/sketchup/user_avatar/forums.sketchup.com/danrathbun/32/500_2.png) [@DanRathbun](https://forums.sketchup.com/u/DanRathbun)\ **Post date:** [April 9, 2025, 9:14pm UTC](https://forums.sketchup.com/t/ruby-script-for-texture-positioning/322437/4 "2025-04-09T21:14:49Z")
> [@evgeny27](#): > > I never even considered that position\_material’s UV mapping starts from the top-left. That is what I **thought** from testing. But I am not so sure now. The API documentation is not absolutely clear. What has me questioning it now, is [`Sketchup::ImageRep#color_at_uv()`](https://ruby.sketchup.com/Sketchup/ImageRep.html#color_at_uv-instance_method) which says: > The [#color\_at\_uv](https://ruby.sketchup.com/Sketchup/ImageRep.html#color_at_uv-instance_method) method returns a color corresponding to the UV texture coordinates. **0.0, 0.0 maps to the bottom left and 1.0, 1.0 to the top right of the image**. (_Emboldening by me_.) Since an `ImageRep` is the internal representation of material textures, this may be a good “clue”. Also, look at [`Geom::PolygonMesh#set_uv()`](https://ruby.sketchup.com/Geom/PolygonMesh.html#set_uv-instance_method)and it’s example snippet. The API docs could use a little primer of UVs and SketchUp geometry in the [**Files**](https://ruby.sketchup.com/file_list.html) section. * * * I think @thomthom has a UV helper / inspection utility that may help in development. - [UV Toolkit² | SketchUp Extension Warehouse](https://extensions.sketchup.com/extension/b3855845-ff9d-46d3-89cd-42830dcc5f74/uv-toolkit) ---
**Author:** ![thomthom](https://sea2.discourse-cdn.com/sketchup/user_avatar/forums.sketchup.com/thomthom/32/12606_2.png) [@thomthom](https://forums.sketchup.com/u/thomthom)\ **Post date:** [May 8, 2025, 7:11pm UTC](https://forums.sketchup.com/t/ruby-script-for-texture-positioning/322437/5 "2025-05-08T19:11:30Z")
> [@evgeny27](#): > > face.position\_material(material, pt0, pt1, pt2) The points given should be pairs of world and UV - from 1 to 4 pairs depending on what you need to control the position, orientation, scale, shear and perspective projection. To pin a texture to a face: ```auto points = [ Geom::Point3d.new(0, 0, 1), Geom::Point3d.new(9, 0, 1), Geom::Point3d.new(9, 9, 1), Geom::Point3d.new(0, 9, 1), ] face = entities.add_face(points) uvs = [ Geom::Point3d.new(0, 0), Geom::Point3d.new(1, 0), Geom::Point3d.new(1, 1), Geom::Point3d.new(0, 1), ] mapping = points.zip(uvs) # Mapping then looks like this: [ Geom::Point3d.new(0, 0, 1), # World Geom::Point3d.new(0, 0), # UV Geom::Point3d.new(9, 0, 1), # World Geom::Point3d.new(1, 0), # UV Geom::Point3d.new(9, 9, 1), # World Geom::Point3d.new(1, 1), # UV Geom::Point3d.new(0, 9, 1), # World Geom::Point3d.new(0, 1), # UV ] face.position_material(material, mapping, true) ```