Access Texture Mappings from Objects Inside Block Definitions

Rhino Developer
1

Question:

I’m developing a Rhino C++ plugin that saves and restores texture mappings for objects. The save/restore works perfectly for regular objects in the document, but I’m struggling to access texture mappings from objects inside block definitions.

What Works:

  • Saving/restoring texture mappings for regular objects using obj->Attributes().m_rendering_attributes.m_mappings

  • Finding block instances that have an elementId user attribute

  • Getting the block definition from the instance

What Doesn’t Work:

  • Accessing texture mapping data from objects inside block definitions

Approaches Tried:

1. Direct Access (Causes Crashes):

const CRhinoInstanceDefinition* idef = // ... get definition
int obj_count = idef->ObjectCount();

for (int i = 0; i < obj_count; i++)
{
    const CRhinoObject* obj = idef->Object(i);
    const ON_3dmObjectAttributes& attribs = obj->Attributes();
    // Access violation when trying to read:
    int mapping_count = attribs.m_rendering_attributes.m_mappings.Count();
}

This crashes with an access violation at opennurbs_array_defs.h:1074 - the internal m_mappings array appears to be in a corrupted/invalid state for objects inside block definitions.

2. Block Edit Mode via Script (Commands Don’t Exist):

// Select block instance
RhinoApp().RunScript(doc->RuntimeSerialNumber(), L"_SelId <uuid>", 0);

// Try to enter block edit mode - ALL FAIL with "Unknown command"
RhinoApp().RunScript(doc->RuntimeSerialNumber(), L"BlockEdit", 0);
RhinoApp().RunScript(doc->RuntimeSerialNumber(), L"-BlockEdit", 0); 
RhinoApp().RunScript(doc->RuntimeSerialNumber(), L"_BlockEdit", 0);
RhinoApp().RunScript(doc->RuntimeSerialNumber(), L"EditBlockInPlace", 0);

All variations return “Unknown command” in the Rhino command line.

Question: What is the correct way to programmatically access texture mapping information from objects inside block definitions in the C++ SDK?

Specifically:

  1. Is there a C++ API method to enter block edit mode (similar to RhinoCommon’s InstanceDefinitionTable.ModifyGeometry)?

  2. Is there a safe way to access object attributes from block definition objects without triggering access violations?

  3. Are there any special considerations or different APIs for accessing rendering attributes of objects inside blocks vs. regular objects?

Environment:

  • Rhino C++ SDK

  • Working with Speckle-generated blocks (long auto-generated block names)

  • Need to save/restore texture mappings to survive geometry refresh operations

Any guidance would be greatly appreciated!

2

Here is some context for why I’m trying to do this, I’m using Speckle to load geometry sent from Revit as we design in Revit and Rhino but render only from Rhino. Every time Speckle loads geometry, it wipes the texture mappings from all the objects, so we want to be able to save them first, load Speckle, then restore mappings.

RestoreTextureMappings

3

Can you share some geometry with textures?

4

Absolutely, I’ve included 2 files, one with the mappings applied to meshes and blocks (Example_with_mappings.3dm) and then the other after a Speckle reload where the mappings have been cleared (Example_after_Speckle_no_mappings.3dm).

For additional context we do most of the mapping with “Apply box mapping” but we do have some cases where we use planar, cylinder or surface.

image
image1657×831 209 KB

Examples.zip (13.9 MB)

5

I was just curious whether the mapping type could be retrieved with Grasshopper:

image
image1786×849 100 KB

Weird that it does not show the surface mapping type on the 3x8 beam which isn’t vertical.

image
image1380×758 78.6 KB

6

That might be correct, in Rhino it shows Surface mapping even when there is no mapping applied to the object and I didn’t apply any mapping to that block.

Are we able to save those mappings to file and then reapply them?

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