NativeEngine: MultiRenderTarget framebuffers + OIT alpha blend modes by bkaradzic-microsoft · Pull Request #1754 · BabylonJS/BabylonNative

bkaradzic-microsoft · 2026-06-11T17:46:19Z

Paired engine PR: BabylonJS/Babylon.js#18568

What

Foundational native support for MultiRenderTarget (MRT) and the order-independent-transparency blend
modes, removing several "engine._gl is null" crash classes. It does not by itself turn the
MRT/OIT/FrameGraph validation tests green — those need further work (see Follow-ups).

Changes

Plugins/NativeEngine/Source/NativeEngine.cpp / .h
- CreateFrameBuffer and CreateMultiFrameBuffer now share a private
  CreateFrameBufferImpl(env, colorTextures, …) helper that builds one bgfx framebuffer with N color
  attachments (+ an optional depth/stencil attachment), so a MultiRenderTarget renders to all
  targets at once (bgfx writes every attachment of the bound framebuffer — no drawBuffers needed).
  The two N-API methods are kept for protocol compatibility and only differ in how they parse
  info[0] (single nullable texture vs. array); the single-RT path is just the 0-or-1-color case.
  The shared helper validates the attachment count against caps->limits.maxFBAttachments and keeps
  the "Stencil without depth…" warning and the isTextureValid assert.
- Add alpha blend modes ALPHA_ONEONE_ONEONE (11) and ALPHA_LAYER_ACCUMULATE (17) used by the
  depth-peeling OIT renderer.

Paired engine PR

Pairs with the Babylon.js change (createMultipleRenderTarget + MRT helper overrides, applyStates
override, reverse-Z clear, alpha-mode mapping). That PR feature-detects both createMultiFrameBuffer
and the two alpha constants, so it degrades gracefully on native binaries that predate this PR.

CI

The validation suite uses the published babylonjs npm, which doesn't yet contain the paired JS, so
no new tests are enabled here and CI stays in the usual "pending dep bump" state. Verified locally
against a babylon.max.js built from the paired branch, and the plugin compiles clean
(cmake --build build/win32 --target NativeEngine --config RelWithDebInfo).

Follow-ups (separate work)

OIT depth-peeling still faults inside the D3D11 driver on submit (multi-output / SRV↔RTV
ping-pong); needs interactive GPU debugging (PIX / VS Graphics Debugger).
Native does not yet apply the blend equation (MAX) — setAlphaEquation is a no-op — so OIT
blending would still be incorrect after the crash is fixed.
2D-array / cube color attachments for MRT are approximated as 2D (test "MRT with different texture
types").

Related PRs & landing order

Babylon.js (engine / TS): [Native] MultiRenderTarget, reverse-Z clear, applyStates, OIT alpha modes Babylon.js#18568
BabylonNative (C++ engine): NativeEngine: MultiRenderTarget framebuffers + OIT alpha blend modes #1754

These two are co-dependent and land in this order:

Babylon.js #18568 first — it only adds native-engine TS overrides, changes no WebGL behavior,
re-enables no validation tests on its own, and feature-detects this PR's additions, so it can merge
independently.
A babylonjs npm release ships that TS change.
BabylonNative NativeEngine: MultiRenderTarget framebuffers + OIT alpha blend modes #1754 last — after bumping the bundled babylonjs to that release. (This
foundational pair does not yet turn the MRT/OIT/FrameGraph tests green — that is separate follow-up
work.)

bghgary

[Reviewed by Copilot on behalf of @bghgary]

One refactor comment inline.

bghgary

[Reviewed by Copilot on behalf of @bghgary]

LGTM. The description is now stale, though: since #18568 feature-detects the native surface, the "co-dependent / landing order" framing no longer applies — the two can land separately, and this can come out of draft.

Copilot

Pull request overview

This PR adds foundational NativeEngine support for MultiRenderTarget framebuffers by creating a single bgfx framebuffer with N color attachments (plus optional depth/stencil), and exposes two additional alpha blend modes needed by OIT depth-peeling workflows. It also updates the bundled Babylon.js npm dependencies used by the Apps workspace.

Changes:

Add createMultiFrameBuffer and refactor framebuffer creation into a shared CreateFrameBufferImpl that supports multiple color attachments.
Expose additional alpha blend mode constants (ALPHA_ONEONE_ONEONE, ALPHA_LAYER_ACCUMULATE) for native-side blend state mapping.
Bump Babylon.js-related npm dependencies in Apps/ to ^9.15.0 (and update lockfile).

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
Plugins/NativeEngine/Source/NativeEngine.h	Declares new MRT framebuffer entrypoint and shared framebuffer helper.
Plugins/NativeEngine/Source/NativeEngine.cpp	Implements MRT framebuffer creation via a shared helper; adds OIT blend mode constants and JS binding for `createMultiFrameBuffer`.
Apps/package.json	Updates Babylon.js package dependency versions to `^9.15.0`.
Apps/package-lock.json	Locks Babylon.js packages to `9.15.0` and updates related integrity metadata.

Files not reviewed (1)

Apps/package-lock.json: Generated file

bkaradzic-microsoft · 2026-07-08T23:13:28Z

+        if (colorCount + 1 > caps->limits.maxFBAttachments)
+        {
+            throw Napi::Error::New(env, "Invalid number of color attachments for frame buffer");
+        }


Fixed in 05862e2. The guard now reserves the depth/stencil slot only when one is generated: const uint32_t depthStencilCount = (generateStencilBuffer || generateDepth) ? 1u : 0u; then checks colorCount + depthStencilCount > caps->limits.maxFBAttachments. This matches the attachment-creation path below (which only appends the depth/stencil attachment inside the same generateStencilBuffer || generateDepth branch), so a max-color-count MRT with no depth/stencil is no longer wrongly rejected.

Foundational native-engine support for MultiRenderTarget (MRT) and the order- independent-transparency blend modes, removing several "engine._gl is null" crash classes. It does not by itself land the MRT/OIT/FrameGraph validation tests, which need further work (see follow-ups below). - Add NativeEngine::CreateMultiFrameBuffer: build one bgfx framebuffer with N color attachments (+ optional depth) so a MultiRenderTarget renders to all targets at once (bgfx writes every attachment of the bound framebuffer, so no drawBuffers is needed). JS-controlled attachment count is validated against caps->limits.maxFBAttachments. - Add alpha blend modes ALPHA_ONEONE_ONEONE (11) and ALPHA_LAYER_ACCUMULATE (17) used by the depth-peeling OIT renderer. Pairs with the Babylon.js change (createMultipleRenderTarget + MRT helper overrides, applyStates, reverse-Z clear). Known follow-ups: the OIT depth- peeling path still faults inside the D3D11 driver on submit (needs interactive GPU debugging), and the blend equation (MAX) is not yet applied natively. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…ed helper Address review feedback (discussion_r3546780088): the single- and multi-RT framebuffer paths were ~95% identical. Extract the shared color/depth attachment setup, framebuffer creation and cleanup into a private CreateFrameBufferImpl helper. Both N-API methods are kept so the protocol is unchanged; they now only differ in how they parse info[0] (single nullable texture vs. array) before calling the shared helper. This restores the "Stencil without depth..." warning and the isTextureValid assert that the multi path had dropped, and lets the single-RT path be the 0-or-1-color case (the shared helper no longer rejects colorCount == 0). The maxFBAttachments upper-bound guard is preserved. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The attachment-count guard in CreateFrameBufferImpl unconditionally added 1 for a depth/stencil attachment (colorCount + 1), which incorrectly rejected a valid MRT that uses the maximum number of color attachments with no depth/stencil (generateDepth=false, generateStencilBuffer=false). Reserve the depth/stencil slot only when one is actually generated, matching the attachment-creation logic below. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…odes (#18568) Paired native PR: BabylonJS/BabylonNative#1754 ## What Foundational native-engine surface so `MultiRenderTarget`, the reverse depth buffer, and the order-independent-transparency (depth-peeling) renderer stop dereferencing the null `_gl` context. This removes several distinct crash classes. It does **not** by itself turn the MRT/OIT/FrameGraph validation tests green — those need further work (see Follow-ups). ## Changes (`packages/dev/core/src/Engines`) - **`thinNativeEngine.pure.ts`** - `createMultipleRenderTarget` + the MRT helper overrides: `bindAttachments`, `buildTextureLayout`, `restoreSingleAttachment`/`restoreSingleAttachmentForRenderTarget`, `generateMipMapsMultiFramebuffer`, `resolveMultiFramebuffer`, `unBindMultiColorAttachmentFramebuffer`, `updateMultipleRenderTargetTextureSampleCount`. bgfx writes every color attachment of the bound framebuffer, so the WebGL `drawBuffers` / MSAA-resolve plumbing becomes no-ops on Native. Reports `drawBuffersExtension = true`. - `clear()`: implement the reverse depth buffer (clear depth to 0 + `GEQUAL`) instead of throwing. - `applyStates()`: override so it flushes the depth-culling state through the native command path — the base implementation drives the null `_gl` directly, which crashed callers that mutate `engine.depthCullingState` then call `applyStates()` (e.g. the OIT depth-peeling renderer). - **`Native/nativeHelpers.ts` / `nativeInterfaces.ts`**: map alpha modes `ALPHA_ONEONE_ONEONE` and `ALPHA_LAYER_ACCUMULATE` to the native engine, and declare `createMultiFrameBuffer`. ## Backward compatibility (feature detection) `createMultiFrameBuffer` and the two OIT alpha constants only exist on a Babylon Native binary that carries the paired #1754. They are declared **optional** on the native interface and feature-detected at runtime, so this PR runs against the currently-published native **without** a protocol/version bump: - `createMultiFrameBuffer` absent → `Logger.Warn` + fall back to a single-attachment `createFrameBuffer` bound to the first color target. - `ALPHA_ONEONE_ONEONE` / `ALPHA_LAYER_ACCUMULATE` absent → warn once + fall back to `ALPHA_ONEONE`. This is also what fixes the previously-red **"Native tests (experimental)"** CI job, which pulls the BabylonNative *master* Playground (no #1754): before the guards it hit `createMultiFrameBuffer is not a function` / an `undefined` alpha mode, the harness exited on the first failure, and the step's retries blew the job timeout. With the guards the MRT/OIT scenes degrade gracefully instead of crashing. ## Paired native PR Pairs with the BabylonNative C++ change (the shared `CreateFrameBufferImpl` framebuffer helper + the two alpha blend modes). Thanks to the feature detection above, this JS PR can land **before** #1754. ## Follow-ups (not in this PR) - OIT depth-peeling (`thinDepthPeelingRenderer`) still faults inside the D3D11 driver on `submit` (a multi-output / SRV↔RTV ping-pong state the driver rejects); needs interactive GPU debugging. - The blend **equation** (e.g. `MAX`) is not yet applied on Native (`setAlphaEquation` is a no-op), so OIT blending would still be incorrect once the crash is resolved. ## Testing - `nx run babylonjs:build` (full `tsc -b` + rollup + declaration) and ESLint pass. - Against native **with** #1754: built `babylon.max.js` and ran the BabylonNative Playground suite (D3D11). MRT, reverse-Z, and the depth-peeling setup no longer crash with `COLOR_ATTACHMENT0` / `reverse depth buffer` / `depthMask of undefined` / `Unsupported alpha mode`. No regressions in existing 2D render-target tests. - Against native **without** #1754: the feature-detection guards keep those same scenes from throwing — they warn and degrade to a single-attachment framebuffer + `ALPHA_ONEONE`. --- ## Related PRs & landing order - **Babylon.js (engine / TS):** #18568 - **BabylonNative (C++ engine):** BabylonJS/BabylonNative#1754 These two are co-dependent. With the feature-detection guards, **#18568 no longer hard-requires the native side** and can merge independently: 1. **Babylon.js #18568 first** — adds native-engine TS overrides, changes no WebGL behavior, re-enables no validation tests on its own, and degrades gracefully on native that predates #1754. 2. A **`babylonjs` npm release** ships that TS change. 3. **BabylonNative #1754 last** — after bumping the bundled `babylonjs` to that release. (This foundational pair does not yet turn the MRT/OIT/FrameGraph tests green — that is separate follow-up work.) --------- Co-authored-by: Branimir Karadzic <branimirkaradzic@gmail.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

bkaradzic-microsoft mentioned this pull request Jun 11, 2026

[Native] MultiRenderTarget, reverse-Z clear, applyStates, OIT alpha modes BabylonJS/Babylon.js#18568

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bkaradzic-microsoft force-pushed the native-multi-render-target branch from c773272 to db75d2e Compare June 18, 2026 15:22

bkaradzic-microsoft force-pushed the native-multi-render-target branch from db75d2e to 1b4cbd0 Compare July 6, 2026 15:14

bkaradzic-microsoft requested a review from bghgary July 8, 2026 15:15

bghgary requested changes Jul 8, 2026

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Comment thread Plugins/NativeEngine/Source/NativeEngine.cpp

bghgary approved these changes Jul 8, 2026

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bkaradzic-microsoft marked this pull request as ready for review July 8, 2026 22:59

Copilot AI review requested due to automatic review settings July 8, 2026 22:59

Copilot started reviewing on behalf of bkaradzic-microsoft July 8, 2026 23:00 View session

Copilot AI reviewed Jul 8, 2026

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bkaradzic and others added 2 commits July 8, 2026 16:07

bkaradzic-microsoft force-pushed the native-multi-render-target branch from 04f709e to 779fc34 Compare July 8, 2026 23:07

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NativeEngine: MultiRenderTarget framebuffers + OIT alpha blend modes#1754

NativeEngine: MultiRenderTarget framebuffers + OIT alpha blend modes#1754
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bkaradzic-microsoft commented Jun 11, 2026 •

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