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NativeEngine: MultiRenderTarget framebuffers + OIT alpha blend modes #1754

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531ac59
NativeEngine: MultiRenderTarget framebuffers + OIT alpha blend modes
bkaradzic Jun 11, 2026
779fc34
NativeEngine: fold CreateFrameBuffer/CreateMultiFrameBuffer into shar…
bkaradzic Jul 8, 2026
05862e2
NativeEngine: only reserve depth/stencil FB slot when generated
bkaradzic Jul 8, 2026
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60 changes: 54 additions & 6 deletions Plugins/NativeEngine/Source/NativeEngine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,8 @@ namespace Babylon
constexpr uint64_t MULTIPLY = BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_DST_COLOR, BGFX_STATE_BLEND_ZERO, BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_ONE);
constexpr uint64_t MAXIMIZED = BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_SRC_ALPHA, BGFX_STATE_BLEND_INV_SRC_COLOR, BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_ONE);
constexpr uint64_t ONEONE = BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_ZERO, BGFX_STATE_BLEND_ONE);
constexpr uint64_t ONEONE_ONEONE = BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_ONE);
constexpr uint64_t LAYER_ACCUMULATE = BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_SRC_ALPHA, BGFX_STATE_BLEND_INV_SRC_ALPHA, BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_INV_SRC_ALPHA);
constexpr uint64_t PREMULTIPLIED = BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_INV_SRC_ALPHA, BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_ONE);
constexpr uint64_t PREMULTIPLIED_PORTERDUFF = BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_INV_SRC_ALPHA, BGFX_STATE_BLEND_ONE, BGFX_STATE_BLEND_INV_SRC_ALPHA);
constexpr uint64_t INTERPOLATE = BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_FACTOR, BGFX_STATE_BLEND_INV_FACTOR, BGFX_STATE_BLEND_FACTOR, BGFX_STATE_BLEND_INV_FACTOR);
Expand Down Expand Up @@ -598,6 +600,8 @@ namespace Babylon
StaticValue("ALPHA_MULTIPLY", Napi::Number::From(env, AlphaMode::MULTIPLY)),
StaticValue("ALPHA_MAXIMIZED", Napi::Number::From(env, AlphaMode::MAXIMIZED)),
StaticValue("ALPHA_ONEONE", Napi::Number::From(env, AlphaMode::ONEONE)),
StaticValue("ALPHA_ONEONE_ONEONE", Napi::Number::From(env, AlphaMode::ONEONE_ONEONE)),
StaticValue("ALPHA_LAYER_ACCUMULATE", Napi::Number::From(env, AlphaMode::LAYER_ACCUMULATE)),
StaticValue("ALPHA_PREMULTIPLIED", Napi::Number::From(env, AlphaMode::PREMULTIPLIED)),
StaticValue("ALPHA_PREMULTIPLIED_PORTERDUFF", Napi::Number::From(env, AlphaMode::PREMULTIPLIED_PORTERDUFF)),
StaticValue("ALPHA_INTERPOLATE", Napi::Number::From(env, AlphaMode::INTERPOLATE)),
Expand Down Expand Up @@ -726,6 +730,7 @@ namespace Babylon
InstanceMethod("resizeImageBitmap", &NativeEngine::ResizeImageBitmap),

InstanceMethod("createFrameBuffer", &NativeEngine::CreateFrameBuffer),
InstanceMethod("createMultiFrameBuffer", &NativeEngine::CreateMultiFrameBuffer),

InstanceMethod("getRenderWidth", &NativeEngine::GetRenderWidth),
InstanceMethod("getRenderHeight", &NativeEngine::GetRenderHeight),
Expand Down Expand Up @@ -1853,12 +1858,55 @@ namespace Babylon
const bool generateDepth = info[4].As<Napi::Boolean>();
const uint32_t samples = info[5].IsUndefined() ? 1 : info[5].As<Napi::Number>().Uint32Value();

std::array<bgfx::Attachment, 2> attachments{};
// A single render target is just the zero-or-one color attachment case of the shared implementation.
Graphics::Texture* const colorTextures[]{texture};
const gsl::span<Graphics::Texture* const> colorAttachments{colorTextures, texture != nullptr ? 1u : 0u};

return CreateFrameBufferImpl(info.Env(), colorAttachments, width, height, generateStencilBuffer, generateDepth, samples);
}

Napi::Value NativeEngine::CreateMultiFrameBuffer(const Napi::CallbackInfo& info)
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{
const auto colorTexturesArray = info[0].As<Napi::Array>();
const uint16_t width = static_cast<uint16_t>(info[1].As<Napi::Number>().Uint32Value());
const uint16_t height = static_cast<uint16_t>(info[2].As<Napi::Number>().Uint32Value());
const bool generateStencilBuffer = info[3].As<Napi::Boolean>();
const bool generateDepth = info[4].As<Napi::Boolean>();
const uint32_t samples = info[5].IsUndefined() ? 1 : info[5].As<Napi::Number>().Uint32Value();

const uint32_t colorCount = colorTexturesArray.Length();
// BGFX_CONFIG_MAX_FRAME_BUFFER_ATTACHMENTS is 8, so at most 8 color attachments fit alongside the depth attachment.
std::array<Graphics::Texture*, 8> colorTextures{};
if (colorCount > colorTextures.size())
{
throw Napi::Error::New(info.Env(), "Invalid number of color attachments for multi render target frame buffer");
}

for (uint32_t i = 0; i < colorCount; ++i)
{
colorTextures[i] = colorTexturesArray.Get(i).As<Napi::Pointer<Graphics::Texture>>().Get();
}

return CreateFrameBufferImpl(info.Env(), gsl::span<Graphics::Texture* const>{colorTextures.data(), colorCount}, width, height, generateStencilBuffer, generateDepth, samples);
}

Napi::Value NativeEngine::CreateFrameBufferImpl(Napi::Env env, gsl::span<Graphics::Texture* const> colorTextures, uint16_t width, uint16_t height, bool generateStencilBuffer, bool generateDepth, uint32_t samples)
{
const bgfx::Caps* caps = bgfx::getCaps();
const uint32_t colorCount = static_cast<uint32_t>(colorTextures.size());
// One slot per color attachment plus a single depth/stencil attachment. bgfx caps the total via
// maxFBAttachments; reject out-of-range counts up front rather than relying on the validation assert.
if (colorCount + 1 > caps->limits.maxFBAttachments)
{
throw Napi::Error::New(env, "Invalid number of color attachments for frame buffer");
}

@bkaradzic-microsoft bkaradzic-microsoft Jul 8, 2026

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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.


// BGFX_CONFIG_MAX_FRAME_BUFFER_ATTACHMENTS is 8, so 8 color + 1 depth fits in a fixed array.
std::array<bgfx::Attachment, 9> attachments{};
uint8_t numAttachments = 0;

if (texture != nullptr)
for (Graphics::Texture* texture : colorTextures)
{
const bgfx::Caps* caps = bgfx::getCaps();
// bgfx validation now asserts when trying to use BGFX_RESOLVE_AUTO_GEN_MIPS with a texture that doesn't have the BGFX_CAPS_FORMAT_TEXTURE_MIP_AUTOGEN flag,
// but before it would just ignore the flag and not generate mips without any warning. This prevents validation assert, but rendering might be broken if autogen
// mips were expected. Basically this change preserves previous behavior.
Expand All @@ -1873,7 +1921,7 @@ namespace Babylon
{
if (generateStencilBuffer && !generateDepth)
{
JsConsoleLogger::LogWarn(info.Env(), "Stencil without depth is not supported, assuming depth and stencil");
JsConsoleLogger::LogWarn(env, "Stencil without depth is not supported, assuming depth and stencil");
}

auto flags = BGFX_TEXTURE_RT_WRITE_ONLY | RenderTargetSamplesToBgfxMsaaFlag(samples);
Expand Down Expand Up @@ -1905,11 +1953,11 @@ namespace Babylon
bgfx::destroy(depthStencilTextureHandle);
}

throw Napi::Error::New(info.Env(), "Failed to create frame buffer");
throw Napi::Error::New(env, "Failed to create frame buffer");
}

Graphics::FrameBuffer* frameBuffer = new Graphics::FrameBuffer(m_deviceContext, frameBufferHandle, width, height, false, generateDepth, generateStencilBuffer, depthStencilAttachmentIndex);
return Napi::Pointer<Graphics::FrameBuffer>::Create(info.Env(), frameBuffer, Napi::NapiPointerDeleter(frameBuffer));
return Napi::Pointer<Graphics::FrameBuffer>::Create(env, frameBuffer, Napi::NapiPointerDeleter(frameBuffer));
}

// TODO: This doesn't get called when an Engine instance is disposed.
Expand Down
7 changes: 7 additions & 0 deletions Plugins/NativeEngine/Source/NativeEngine.h
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,11 @@

namespace Babylon
{
namespace Graphics
{
class Texture;
}

class NativeEngine final : public Napi::ObjectWrap<NativeEngine>
{
static constexpr auto JS_CLASS_NAME = "_NativeEngine";
Expand Down Expand Up @@ -115,6 +120,8 @@ namespace Babylon
void DeleteTexture(const Napi::CallbackInfo& info);
Napi::Value ReadTexture(const Napi::CallbackInfo& info);
Napi::Value CreateFrameBuffer(const Napi::CallbackInfo& info);
Napi::Value CreateMultiFrameBuffer(const Napi::CallbackInfo& info);
Napi::Value CreateFrameBufferImpl(Napi::Env env, gsl::span<Graphics::Texture* const> colorTextures, uint16_t width, uint16_t height, bool generateStencilBuffer, bool generateDepth, uint32_t samples);
void DeleteFrameBuffer(NativeDataStream::Reader& data);
void BindFrameBuffer(NativeDataStream::Reader& data);
void UnbindFrameBuffer(NativeDataStream::Reader& data);
Expand Down
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