{"record":{"id":"d18b16faa639da40","repo":"BabylonJS/Babylon.js","slug":"can-t-handle-more-than-8-attachments-for-a-mrt-in","errorCode":null,"errorMessage":"Can't handle more than 8 attachments for a MRT in cache render pipeline!","messagePattern":"Can't handle more than 8 attachments for a MRT in cache render pipeline!","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"packages/dev/core/src/Engines/WebGPU/webgpuCacheRenderPipeline.ts","lineNumber":370,"sourceCode":"        (this.mrtAttachments as any) = attachments;\r\n        let mask = 0;\r\n        for (let i = 0; i < attachments.length; ++i) {\r\n            if (attachments[i] !== 0) {\r\n                mask += 1 << i;\r\n            }\r\n        }\r\n        if (this._mrtEnabledMask !== mask) {\r\n            this._mrtEnabledMask = mask;\r\n            this._isDirty = true;\r\n            this._stateDirtyLowestIndex = Math.min(this._stateDirtyLowestIndex, StatePosition.MRTAttachments);\r\n        }\r\n    }\r\n\r\n    public setMRT(textureArray: InternalTexture[], textureCount?: number): void {\r\n        textureCount = textureCount ?? textureArray.length;\r\n        if (textureCount > 8) {\r\n            // We only support 8 MRTs in WebGPU, so we throw an error if we try to set more than that.\r\n            throw new Error(\"Can't handle more than 8 attachments for a MRT in cache render pipeline!\");\r\n        }\r\n        (this.mrtTextureArray as any) = textureArray;\r\n        (this.mrtTextureCount as any) = textureCount;\r\n\r\n        // Since we need approximately 45 different values per texture format (see WebGPUTextureManager.renderableTextureFormatToIndex), we use 6 bits to encode a texture format,\r\n        // which means we can encode 8 texture formats in 48 bits (a double can represent integers exactly up until 2^53, so 48 bits is ok).\r\n\r\n        this._mrtEnabledMask = 0xffff; // all textures are enabled at start (meaning we can write to them). Calls to setMRTAttachments may disable some\r\n\r\n        let mrtAttachments = 0;\r\n        let mask = 0;\r\n\r\n        for (let i = 0; i < textureCount; ++i) {\r\n            const texture = textureArray[i];\r\n            const gpuWrapper = texture?._hardwareTexture as Nullable<WebGPUHardwareTexture>;\r\n\r\n            this._mrtFormats[i] = gpuWrapper?.format ?? this._webgpuColorFormat[0];\r\n\r","sourceCodeStart":352,"sourceCodeEnd":388,"githubUrl":"https://github.com/BabylonJS/Babylon.js/blob/0592b347b8a4ee0236089ea86a749cacfdb266d8/packages/dev/core/src/Engines/WebGPU/webgpuCacheRenderPipeline.ts#L352-L388","documentation":"WebGPUCacheRenderPipeline.setMRT enforces the WebGPU limit of 8 color attachments per render pass. Passing an InternalTexture array (or textureCount) larger than 8 throws, because the pipeline cache encodes at most 8 MRT attachments.","triggerScenarios":"Calling setMRT with an array of more than 8 internal textures, or passing an explicit textureCount > 8, typically through engine device reset/pipeline setup paths that wire many render targets.","commonSituations":"Custom MRT setups with 9+ render targets (e.g. G-buffer with many attachments); porting a Vulkan/DirectX engine with higher MRT limits to WebGPU; miscomputed textureCount from a bad length.","solutions":["Reduce the number of simultaneous render targets to at most 8 (merge/pack attachments, e.g. into RGBA channels).","Split the rendering into multiple passes, writing a subset of targets per pass.","Verify the textureCount argument; pass it explicitly only when it correctly equals the attachment count."],"exampleFix":"// before\npipeline.setMRT([t0,t1,t2,t3,t4,t5,t6,t7,t8]); // 9 targets\n// after\npipeline.setMRT([t0,t1,t2,t3,t4,t5,t6,t7]); // pack extra data or use a second pass","handlingStrategy":"validation","validationCode":"if (textureArray.length > 8 || (textureCount ?? textureArray.length) > 8) {\n  throw new RangeError('WebGPU supports at most 8 MRT attachments; reduce or pack render targets');\n}\npipeline.setMRT(textureArray, textureCount);","typeGuard":"function fitsWebGPUMrt(textures: unknown[], count?: number): textures is BABYLON.InternalTexture[] {\n  return textures.length <= 8 && (count ?? textures.length) <= 8;\n}","tryCatchPattern":"try {\n  pipeline.setMRT(textures, count);\n} catch (e) {\n  if (String(e.message).includes('more than 8 attachments')) {\n    pipeline.setMRT(textures.slice(0, 8), 8); // render remaining targets in a second pass\n  } else throw e;\n}","preventionTips":["Design G-buffers with a maximum of 8 color attachments when targeting WebGPU.","Pack several scalar outputs into one RGBA target via channel packing.","Split wide-MRT rendering into multiple passes."],"tags":["babylonjs","webgpu","mrt","render-targets","limit-exceeded"],"backgroundTag":"mrt-attachment-limit-exceeded","analyzedSha":"0592b347b8a4ee0236089ea86a749cacfdb266d8","analyzedAt":"2026-08-30T15:11:20.442Z","schemaVersion":2},"datasetVersion":"2026-08-30T18:17:15.746Z"}