# Hydra **URL:** https://forum.aousd.org/c/community/hydra/8.md?page=1 [Latest](https://forum.aousd.org/latest.md) · [Categories](https://forum.aousd.org/categories.md) · [Tags](https://forum.aousd.org/tags.md) **Page:** 2 --- ## [Hydra 2.0 Instance Selection](https://forum.aousd.org/t/hydra-2-0-instance-selection/2755)
**Author:** [@Nicola](https://forum.aousd.org/u/Nicola)\ **Replies:** 0\ **Last updated:** [October 29, 2025, 8:42am UTC](https://forum.aousd.org/t/hydra-2-0-instance-selection/2755 "2025-10-29T08:42:28Z")
I’m trying to select a subset of the instances in a PointInstancer. I see there is the method UsdImagingGLEngine::AddSelected(SdfPath const &path, int instanceIndex), but looking at the code the instanceIndex is not tak… --- ## [Primvars and Relationships](https://forum.aousd.org/t/primvars-and-relationships/2753)
**Author:** [@dietchmatch](https://forum.aousd.org/u/dietchmatch)\ **Replies:** 5\ **Last updated:** [October 29, 2025, 4:51am UTC](https://forum.aousd.org/t/primvars-and-relationships/2753 "2025-10-29T04:51:32Z")
Hi! I have a Renderman shader on which i’m reading a mesh int primvar ( using PxrPrimvar ) to switch between different textures. This works nicely, but if i create a Relationship on my mesh instead of creating a primva… --- ## [HGI Vulkan Shader Compilation: Ability to target a higher version of SPIR-V](https://forum.aousd.org/t/hgi-vulkan-shader-compilation-ability-to-target-a-higher-version-of-spir-v/2721)
**Author:** [@rlei](https://forum.aousd.org/u/rlei)\ **Replies:** 2\ **Last updated:** [October 12, 2025, 9:26pm UTC](https://forum.aousd.org/t/hgi-vulkan-shader-compilation-ability-to-target-a-higher-version-of-spir-v/2721 "2025-10-12T21:26:40Z")
Hello Hydra team! I’ve been working on a Render Delegate and have been taking advantage of the HGI + glslfx ecosystem which has working smoothly for the most part, so thanks for putting those exposures together! We hav… --- ## [How to readback AOVs from glslfx shader?](https://forum.aousd.org/t/how-to-readback-aovs-from-glslfx-shader/2653)
**Author:** [@Grimmigbeisser](https://forum.aousd.org/u/Grimmigbeisser)\ **Replies:** 3\ **Last updated:** [October 1, 2025, 10:53am UTC](https://forum.aousd.org/t/how-to-readback-aovs-from-glslfx-shader/2653 "2025-10-01T10:53:57Z")
Hi, i am working on a custom outline glslfx shader for hdstorm. My idea was to use the primid and instanceid AOVs for edge detection. I wrote a custom HdxTask, which uses an HdSt\_ImageShaderRenderPass. To supply the AOV… --- ## [Reading texture coords in from HdSceneIndexPrim](https://forum.aousd.org/t/reading-texture-coords-in-from-hdsceneindexprim/2692)
**Author:** [@donboie](https://forum.aousd.org/u/donboie)\ **Replies:** 7\ **Last updated:** [September 25, 2025, 6:29am UTC](https://forum.aousd.org/t/reading-texture-coords-in-from-hdsceneindexprim/2692 "2025-09-25T06:29:45Z")
Hi All, I’ve been experimenting with HdGpGenerativeProcedural and encountered a problem when trying to read textures coordinates from this mesh: Input usd file: def Xform "sopimport1" ( kind = "component" ) { … --- ## [Draw Mode and Unloaded Payloads](https://forum.aousd.org/t/draw-mode-and-unloaded-payloads/695)
**Author:** [@chris.rydalch](https://forum.aousd.org/u/chris.rydalch)\ **Replies:** 4\ **Last updated:** [August 29, 2025, 10:15pm UTC](https://forum.aousd.org/t/draw-mode-and-unloaded-payloads/695 "2025-08-29T22:15:01Z")
One of the examples in the USD WG Assets repot is a Teapot, and a scene demonstrating all of the draw modes. When I open the DrawModes.usd file in usdview with 23.08, and unload the payloads, the draw mode boxes/cards/ax… --- ## [Where to find the UsdLux Reference modified HdEmbree](https://forum.aousd.org/t/where-to-find-the-usdlux-reference-modified-hdembree/2663)
**Author:** [@James](https://forum.aousd.org/u/James)\ **Replies:** 2\ **Last updated:** [August 29, 2025, 2:58pm UTC](https://forum.aousd.org/t/where-to-find-the-usdlux-reference-modified-hdembree/2663 "2025-08-29T14:58:29Z")
We were excited to hear and read the updates to UsdLux documentation and hdEmbree being used as a reference implementation for direct lighting behaviour. However, when we built hdEmbree from OpenUSD 25.08 we noticed tha… --- ## [UsdRenderEngineGL leaves GL state that breaks QPainter overlays in QOpenGLWidget](https://forum.aousd.org/t/usdrenderenginegl-leaves-gl-state-that-breaks-qpainter-overlays-in-qopenglwidget/2639)
**Author:** [@hamed](https://forum.aousd.org/u/hamed)\ **Replies:** 1\ **Last updated:** [August 11, 2025, 11:50am UTC](https://forum.aousd.org/t/usdrenderenginegl-leaves-gl-state-that-breaks-qpainter-overlays-in-qopenglwidget/2639 "2025-08-11T11:50:56Z")
Hello, I’m integrating a UsdImagingGLEngine into a Qt’s OpenGL viewport. After calling UsdImagingGLEngine::render(…) inside QOpenGLWidget::paintGL(), any attempt to draw overlay text using QPainter on the widget produce… --- ## [Support different material binding purposes based on current active display purposes](https://forum.aousd.org/t/support-different-material-binding-purposes-based-on-current-active-display-purposes/2633)
**Author:** [@Mithridates](https://forum.aousd.org/u/Mithridates)\ **Replies:** 0\ **Last updated:** [August 5, 2025, 2:07pm UTC](https://forum.aousd.org/t/support-different-material-binding-purposes-based-on-current-active-display-purposes/2633 "2025-08-05T14:07:13Z")
Problem Description In the current OpenUSD implementation, a render delegate specifies its supported material via the GetMaterialBindingPurpose() function, which means only materials with a matching purpose are instantia… --- ## [How to access subdivided geometry in HdGp?](https://forum.aousd.org/t/how-to-access-subdivided-geometry-in-hdgp/2580)
**Author:** [@jjeziorski](https://forum.aousd.org/u/jjeziorski)\ **Replies:** 3\ **Last updated:** [July 23, 2025, 10:37am UTC](https://forum.aousd.org/t/how-to-access-subdivided-geometry-in-hdgp/2580 "2025-07-23T10:37:34Z")
Is there a way to access subdivided geometry in HdGp procedurals? We’re mostly interested in sharing data between procedurals and render delegate is there a good way that avoid calculating it twice? On a similar note i… --- ## [Primvar overrides for single and multiple level instancing](https://forum.aousd.org/t/primvar-overrides-for-single-and-multiple-level-instancing/2409)
**Author:** [@girish.ramesh](https://forum.aousd.org/u/girish.ramesh)\ **Replies:** 3\ **Last updated:** [July 23, 2025, 9:10am UTC](https://forum.aousd.org/t/primvar-overrides-for-single-and-multiple-level-instancing/2409 "2025-07-23T09:10:51Z")
This is a question regarding primvar overrides for general prims vs instantiable prims. This is a basic setup where we have primvar overrides authored at different levels of instancing, ranging from no instancing to two… --- ## [When using CameraUtilFraming API, what is the expected data outside the dataWindow?](https://forum.aousd.org/t/when-using-camerautilframing-api-what-is-the-expected-data-outside-the-datawindow/2592)
**Author:** [@debloip-adsk](https://forum.aousd.org/u/debloip-adsk)\ **Replies:** 0\ **Last updated:** [July 17, 2025, 7:04pm UTC](https://forum.aousd.org/t/when-using-camerautilframing-api-what-is-the-expected-data-outside-the-datawindow/2592 "2025-07-17T19:04:04Z")
Hello, We are trying to use the CameraUtilFraming to do crop region rendering (so having a certain portion of the viewport rendered with one renderer, with the rest rendered by another). For this we are currently experi… --- ## [Motion blur issue with custom prim adapter going from usd 22 to 24 and renderman from 25 to 26](https://forum.aousd.org/t/motion-blur-issue-with-custom-prim-adapter-going-from-usd-22-to-24-and-renderman-from-25-to-26/2572)
**Author:** [@ashum](https://forum.aousd.org/u/ashum)\ **Replies:** 0\ **Last updated:** [July 10, 2025, 4:41pm UTC](https://forum.aousd.org/t/motion-blur-issue-with-custom-prim-adapter-going-from-usd-22-to-24-and-renderman-from-25-to-26/2572 "2025-07-10T16:41:38Z")
Hi, for our custom primitive adapter we were using “samplePrimvar” to provide data for motion blur. From what it looks the behaviour has changed and now the “samplePrimvar” is not being called. Do you know if there is… --- ## [Cant get SkelAnim working with hydra 2 and v25.05](https://forum.aousd.org/t/cant-get-skelanim-working-with-hydra-2-and-v25-05/2415)
**Author:** [@rishflab](https://forum.aousd.org/u/rishflab)\ **Replies:** 2\ **Last updated:** [July 8, 2025, 8:23am UTC](https://forum.aousd.org/t/cant-get-skelanim-working-with-hydra-2-and-v25-05/2415 "2025-07-08T08:23:27Z")
I can’t get skeletal animation to play using UsdStageSceneIndex/Hydra2 with version v25.05. Has anyone had luck with skel anim, hydra 2 and the new release? hgi = Hgi::CreatePlatformDefaultHgi(); driver = HdDriv… --- ## [Rendering simple image with Python like usdview](https://forum.aousd.org/t/rendering-simple-image-with-python-like-usdview/2562)
**Author:** [@vbd](https://forum.aousd.org/u/vbd)\ **Replies:** 2\ **Last updated:** [July 7, 2025, 2:35pm UTC](https://forum.aousd.org/t/rendering-simple-image-with-python-like-usdview/2562 "2025-07-07T14:35:53Z")
Hi! I successfully cloned and built OpenUSD 25.5.1 and can run usdview. Now I’m trying to write a “Hello Hydra” application in Python that renders a simple image to buffer or file - very similar in functionality to usdv… --- ## [HdPrman for Maya](https://forum.aousd.org/t/hdprman-for-maya/2549)
**Author:** [@thornydre](https://forum.aousd.org/u/thornydre)\ **Replies:** 4\ **Last updated:** [July 1, 2025, 12:41pm UTC](https://forum.aousd.org/t/hdprman-for-maya/2549 "2025-07-01T12:41:26Z")
Hello, We are just starting to implement USD into our pipeline, and doing some early testing. We are using Renderman, we managed to have HdPrman running in Maya viewport, but opening a USD file with a PxrSurface materia… --- ## [Scene index invalidation of custom prim types](https://forum.aousd.org/t/scene-index-invalidation-of-custom-prim-types/2544)
**Author:** [@CyrilADSK](https://forum.aousd.org/u/CyrilADSK)\ **Replies:** 4\ **Last updated:** [June 26, 2025, 8:13am UTC](https://forum.aousd.org/t/scene-index-invalidation-of-custom-prim-types/2544 "2025-06-26T08:13:57Z")
Hi, In our render delegate we have custom prim types with custom adapters that we want to port to hydra 2/scene index. I am not sure I understand correctly how the invalidation mechanism should work in that case. Here … --- ## [Material bindings disappear in scene indices](https://forum.aousd.org/t/material-bindings-disappear-in-scene-indices/1939)
**Author:** [@dlanier](https://forum.aousd.org/u/dlanier)\ **Replies:** 4\ **Last updated:** [June 25, 2025, 9:18am UTC](https://forum.aousd.org/t/material-bindings-disappear-in-scene-indices/1939 "2025-06-25T09:18:04Z")
Hi, Summary : I have a problem when assigning a material to a usd prim that didn’t have any material previously, the material bindings get removed by a scene index. More context : This is with usd 24.08 with Hydra 2.… --- ## [Hgi to render directly to OpenGL frame buffer](https://forum.aousd.org/t/hgi-to-render-directly-to-opengl-frame-buffer/2525)
**Author:** [@mxbox](https://forum.aousd.org/u/mxbox)\ **Replies:** 0\ **Last updated:** [June 14, 2025, 2:05am UTC](https://forum.aousd.org/t/hgi-to-render-directly-to-opengl-frame-buffer/2525 "2025-06-14T02:05:25Z")
I am trying to create a simple demo app with Hgi and GLFW. I looked at the file pxr\\imaging\\hgi\\unitTestHelper.cpp as an example, then I ported the relevant functions to my GLFW app. But this file shows how to render t… --- ## [HdMeshUtil::ComputeTriangleIndices and the UsdGeomSubset indices attribute](https://forum.aousd.org/t/hdmeshutil-computetriangleindices-and-the-usdgeomsubset-indices-attribute/2504)
**Author:** [@omnnai](https://forum.aousd.org/u/omnnai)\ **Replies:** 0\ **Last updated:** [June 6, 2025, 4:30am UTC](https://forum.aousd.org/t/hdmeshutil-computetriangleindices-and-the-usdgeomsubset-indices-attribute/2504 "2025-06-06T04:30:19Z")
I am using Hydra for a typical rasterizer with a Vulkan backend. I rely on the HdMeshUtil::ComputeTriangleIndices to produce a single index buffer that can be used for reading from various vertex streams. Some meshes s… --- ## [Hydra2 prim addition order](https://forum.aousd.org/t/hydra2-prim-addition-order/2481)
**Author:** [@CyrilADSK](https://forum.aousd.org/u/CyrilADSK)\ **Replies:** 0\ **Last updated:** [May 28, 2025, 11:32am UTC](https://forum.aousd.org/t/hydra2-prim-addition-order/2481 "2025-05-28T11:32:00Z")
Hi, In our render delegate the lights can have dependencies on a custom type prim, ArnoldNodeGraph, which is very similar to a Material prim. When rendering a test scene, the new scene index system first adds the light … --- ## [Controlling the visibility and transform of a whole usd stage](https://forum.aousd.org/t/controlling-the-visibility-and-transform-of-a-whole-usd-stage/2474)
**Author:** [@dlanier](https://forum.aousd.org/u/dlanier)\ **Replies:** 0\ **Last updated:** [May 23, 2025, 12:51pm UTC](https://forum.aousd.org/t/controlling-the-visibility-and-transform-of-a-whole-usd-stage/2474 "2025-05-23T12:51:20Z")
Hi, In order to control the visibility and transform of all prims from a usd stage in Hydra 2.0, we use a UsdImagingRootOverridesSceneIndex and we add a HdFlatteningSceneIndex (only for visibility and xform) to apply th… --- ## [Questions about VtArray designs/usages to avoid unnecessary COW checks](https://forum.aousd.org/t/questions-about-vtarray-designs-usages-to-avoid-unnecessary-cow-checks/2469)
**Author:** [@WangLumina](https://forum.aousd.org/u/WangLumina)\ **Replies:** 3\ **Last updated:** [May 23, 2025, 6:06am UTC](https://forum.aousd.org/t/questions-about-vtarray-designs-usages-to-avoid-unnecessary-cow-checks/2469 "2025-05-23T06:06:01Z")
Hi team, We notice that when using VtArray, inappropriate usages of operator\[\], emplace\_back, push\_back, etc. can cuase quantities of unnecessary COW checks. Since it’s easy to be misused but can result some performance… --- ## [RPrims with enabled then disabled render purposes are stilled "sync'ed"](https://forum.aousd.org/t/rprims-with-enabled-then-disabled-render-purposes-are-stilled-synced/1514)
**Author:** [@deboisj](https://forum.aousd.org/u/deboisj)\ **Replies:** 2\ **Last updated:** [May 22, 2025, 10:01pm UTC](https://forum.aousd.org/t/rprims-with-enabled-then-disabled-render-purposes-are-stilled-synced/1514 "2025-05-22T22:01:44Z")
Hello, I am working on a render delegate, where I first noticed this issue. But then also saw that it happens in Storm/USDVIEW (tried in different versions, including 0.24.05) Consider this scenario : The USD render p… --- ## [How to setup a zbias and alpha threshold for rendering decals](https://forum.aousd.org/t/how-to-setup-a-zbias-and-alpha-threshold-for-rendering-decals/2449)
**Author:** [@Grimmigbeisser](https://forum.aousd.org/u/Grimmigbeisser)\ **Replies:** 2\ **Last updated:** [May 15, 2025, 6:58am UTC](https://forum.aousd.org/t/how-to-setup-a-zbias-and-alpha-threshold-for-rendering-decals/2449 "2025-05-15T06:58:24Z")
Hi, i am setting up an HdxRenderTask with the following code: auto decoRenderTaskId = GetControllerId().AppendChild(TfToken(“renderTask\_decorations”)); GetRenderIndex()-\>InsertTask(&delegate, decoRenderTaskId); HdxRen… --- ## [Getting HdRenderBuffers with hdPrman](https://forum.aousd.org/t/getting-hdrenderbuffers-with-hdprman/2440)
**Author:** [@tnorth](https://forum.aousd.org/u/tnorth)\ **Replies:** 0\ **Last updated:** [May 11, 2025, 1:11pm UTC](https://forum.aousd.org/t/getting-hdrenderbuffers-with-hdprman/2440 "2025-05-11T13:11:22Z")
Hi, I’ve been using the test code linked below from the USD repo as reference for creating an app to display renderman live rendering but it’s thrown up a few questions: How could I get pointers to HdRenderBuffers to … --- ## [How can I create materials programmatically code with hydra?](https://forum.aousd.org/t/how-can-i-create-materials-programmatically-code-with-hydra/2405)
**Author:** [@orhun](https://forum.aousd.org/u/orhun)\ **Replies:** 4\ **Last updated:** [May 6, 2025, 2:07am UTC](https://forum.aousd.org/t/how-can-i-create-materials-programmatically-code-with-hydra/2405 "2025-05-06T02:07:49Z")
Hi, How can I create materials programmatically with Hydra 2? I have been looking into HdMaterialNetwork2, and HdMaterialNode2, etc, but I am not sure whether I am on the correct path. Are there any resources, you cou… --- ## [HdInstancer::Sync() in Hydra 2.0](https://forum.aousd.org/t/hdinstancer-sync-in-hydra-2-0/2410)
**Author:** [@girish.ramesh](https://forum.aousd.org/u/girish.ramesh)\ **Replies:** 0\ **Last updated:** [April 29, 2025, 4:07pm UTC](https://forum.aousd.org/t/hdinstancer-sync-in-hydra-2-0/2410 "2025-04-29T16:07:51Z")
Hi, We are just experimenting with Hydra 2.0 and wanted to understand what the behaviour of the HdInstancer::Sync() would be in Hydra 2.0. In Hydra 1.x, the behaviour of the Sync() is that it is triggered from any HdRPr… --- ## [StageView and FrameRecorder collision?](https://forum.aousd.org/t/stageview-and-framerecorder-collision/2403)
**Author:** [@berengard](https://forum.aousd.org/u/berengard)\ **Replies:** 0\ **Last updated:** [April 28, 2025, 3:35am UTC](https://forum.aousd.org/t/stageview-and-framerecorder-collision/2403 "2025-04-28T03:35:43Z")
Hello, I’ve ran into some trouble using StageView and FrameRecorder in the same application. My app has a feature for creating a preview render for a given Usd file using Frame Recorder and another feature that opens a… --- ## [Issue with purpose tags visibility not being respected](https://forum.aousd.org/t/issue-with-purpose-tags-visibility-not-being-respected/2391)
**Author:** [@ashum](https://forum.aousd.org/u/ashum)\ **Replies:** 0\ **Last updated:** [April 22, 2025, 4:43pm UTC](https://forum.aousd.org/t/issue-with-purpose-tags-visibility-not-being-respected/2391 "2025-04-22T16:43:09Z")
Hey, I’ve found an issue that causes the unnecessary calls for UpdateForTime and Get in adapters when the purpose visibility of the prim is set to be off. Here is the bug report: Does anyone know why we need to have … [Previous page](https://forum.aousd.org/c/community/hydra/8.md) [Next page](https://forum.aousd.org/c/community/hydra/8.md?page=2)