How many 32-bit variables can I use concurrently in a single thread of a Metal compute kernel without worrying about the variables getting spilled into the device memory? Alternatively: how many 32-bit registers does a single thread have available for itself? Let's say that each thread of my compute kernel needs to store and work with its own array of N float variables, where N can be 128, 256, 512 or more. To achieve maximum possible performance, I do not want to the local thread variables to get spilled into the slow device memory. I want all N variables to be stored "on-chip", in the thread memory space. To make my question more concrete, let's say there is an array thread float localArray[N]. Assuming an unrealistic hypothetical scenario where localArray is the only variable in the whole kernel, what is the maximum value of N for which no portion of localArray would get spilled into the device memory? I searched in the Metal feature set tables, but I could not find any details.

After following the instructions here: https://developer.apple.com/metal/cpp/ I attempted building my project and Xcode presented several errors. In essence it's complaining about some redeclarations in the Metal-CPP headers. NSBundle.hpp and NSError.hpp are included in the metal-cpp/foundation directory from the metal-cpp download. Any help in getting these issues resolved is appreciated. Thanks!

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSBundle allFrameworks]: unrecognized selector sent to instance NS::Bundle* Bundle = NS::Bundle::mainBundle(); Bundle->allFrameworks(); call to allFrameworks() and allBundles() will throw exception, but other functions work well.

I am working on a custom resolve tile shader for a client. I see a big difference in performance depending on where we write to: 1- the resolve texture of the color attachment 2- a rw tile shader texture set via [renderEncoder setTileTexture: myResolvedTexture] Option 2 is more than twice as slow than option 1. Our compute shader writes to 4 UAVs so just using the resolve texture entry is not possible. Why such a difference as there is no more data being written? Can option 2 be as fast as option 1? I can demonstrate the issue in a modified version of the Multisample code sample.

In my project I need to do the following: In runtime create metal Dynamic library from source. In runtime create metal Executable library from source and Link it with my previous created Dynamic library. Create compute pipeline using those two libraries created above. But I get the following error at the third step: Error Domain=AGXMetalG15X_M1 Code=2 "Undefined symbols: _Z5noisev, referenced from: OnTheFlyKernel " UserInfo={NSLocalizedDescription=Undefined symbols: _Z5noisev, referenced from: OnTheFlyKernel } import Foundation import Metal class MetalShaderCompiler { let device = MTLCreateSystemDefaultDevice()! var pipeline: MTLComputePipelineState! func compileDylib() -> MTLDynamicLibrary { let source = """ #include <metal_stdlib> using namespace metal; half3 noise() { return half3(1, 0, 1); } """ let option = MTLCompileOptions() option.libraryType = .dynamic option.installName = "@executable_path/libFoundation.metallib" let library = try! device.makeLibrary(source: source, options: option) let dylib = try! device.makeDynamicLibrary(library: library) return dylib } func compileExlib(dylib: MTLDynamicLibrary) -> MTLLibrary { let source = """ #include <metal_stdlib> using namespace metal; extern half3 noise(); kernel void OnTheFlyKernel(texture2d<half, access::read> src [[texture(0)]], texture2d<half, access::write> dst [[texture(1)]], ushort2 gid [[thread_position_in_grid]]) { half4 rgba = src.read(gid); rgba.rgb += noise(); dst.write(rgba, gid); } """ let option = MTLCompileOptions() option.libraryType = .executable option.libraries = [dylib] let library = try! self.device.makeLibrary(source: source, options: option) return library } func runtime() { let dylib = self.compileDylib() let exlib = self.compileExlib(dylib: dylib) let pipelineDescriptor = MTLComputePipelineDescriptor() pipelineDescriptor.computeFunction = exlib.makeFunction(name: "OnTheFlyKernel") pipelineDescriptor.preloadedLibraries = [dylib] pipeline = try! device.makeComputePipelineState(descriptor: pipelineDescriptor, options: .bindingInfo, reflection: nil) } }

There is a sample project from Apple here. It has a scene of a city at night and you can move in it. It basically has 2 parts: application code written in what looks like Objective-C (I am more familiar with C++), which inherits from things like NSObject, MTKView, NSViewController and so on - it processes input and all app-related and window-related stuff. rendering code that also looks like Objective-C. Btw both parts are mostly in .mm files (Obj-C++ AFAIK). The application part directly uses only one class from the rendering part - AAPLRenderer. I want to move the rendering part to C++ using metal-cpp. For that I need to link metal-cpp to the project. I did it successfully with blank projects several times before using this tutorial. But with this sample project Xcode can't find Foundation/Foundation.hpp (and other metal-cpp headers). The error says this: Did not find header 'Foundation.hpp' in framework 'Foundation' (loaded from '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/System/Library/Frameworks') Pls help

Hey everyone, I’m trying to run Kingdom Come: Deliverance 2 using the Game Porting Toolkit, but I’m encountering a black screen when launching the game. From what I know about the game’s requirements, it might be using Shader Model 6.5, which supports advanced features like DirectX Raytracing (DXR) Tier 1.1. This leads me to suspect that the issue could be related to missing support for DirectX 12.1 Features or Shader Model 6.5 in GPTK. Does anyone know if these features are currently supported by GPTK? If not, are there any plans to implement them in future updates? Alternatively, is there any workaround for games that rely on Shader Model 6.5 and ray tracing? Thanks a lot for your help!

Our app uses Metal for image processing. We have found that if our app (and its possible intensive image processing) is started quickly after user is logged in, then calls to Metal may be hanging/stuck for a good while. Example: it can take 1-2 minutes for something that usually takes 3-5 seconds! Metal threads are just hanging in a memmove... In Activity Monitor we see a lot of things are happening right after log-in. But why Metal calls are blocking for so long is unknown to us... The workaround is to wait a minute before we start our app and start intensive image processing using Metal. But hard to explain this workaround to end-users... It doesn't happen on all computers but fairly easy to reproduce on some computers. We are using macOS 15.3.1. M1/M3 Max. Any good ideas for how to proceed with this problem and possible reach out to Apple engineers? Thanks! :)

The title is self-exploratory. I wasn't able to find the CAMetalDisplayLink on the most recent metal-cpp release (metal-cpp_macOS15_iOS18-beta). Are there any plans to include it in the next release?

Now the examples of metal-cpp are target on desktop and using AppKit which is not supported on iOS. Is there any tips for developing with metal-cpp on mobile device?

When inspecting the geometry in Xcode's metal debugger, I noticed that the shown "frustrum box" didn't make sense. Since Metal uses depth range 0,1 in NDC space, I would expect a vertex that is projected to z:0 to be on the front clipping plane of the frustrum shown in the geometry inspector. This is however not the case. A vertex with ndc z:0 is shown halfway inside the frustrum. Vertices with ndc z less than 0 are correctly culled during rendering, while the geometry inspector's frustrum shows that the vertex is stil inside the frustrum. The image shows vertices that are visually in the middle of the frustrum on z axis, but at the same time the out position shows that they are projected to z:0. How is this possible, unless there's a bug in the geometry inspector?

Hello! I need to "draw" a set of particles into the texture. It would be trivial in render encoder of course. However, I would like to implement the task in compute kernel. Every particle draw operation is expected to set 5 texels - "center" one and left/right/upper/lower. Particles can and will overlap, so concurrent draws are to be expected. I tried using texture atomics - atomic_store() to be more precise. This worked, albeit pretty slowly - too slow for my purpose. Just to test what would happen, I tried using normal texture write(). I was expecting to see some kind of visual artefacts, but to my surprise, it worked very well (and much faster). My question: is it safe? I understand that calling write() doesn't guarantee any ordering of the operations, so if multiple threads write to the same texel, the final value may come from any of those threads. But suppose all the threads were to write the very same color? Can I assume that the texel in question will have said color after the compute kernel finishes? I am using M2 Pro MacBook, but ideally I would love to get the answer for the all Apple Silicon devices. My texture format is R32Int (so as to be able to use atomics), but I could do with any single-channel format, the purpose of the texture is to be binary mask of sorts. Thanks!

I have a bare-bones Metal app setup where I attach a CAMetalLayer to a window that inherits from a NSWindow with a custom delegate. Everything else is vanilla. I'm also using metal-cpp and metal shader converter. I'm running into a issue where the application runs fine in the beginning, but once I resize the window, it starts hitching. It turns out that [CAMetalLayer nextDrawable:] frequently (but not always) takes around a full second (plus or minus a few milliseconds) to return once drawableSize has been updated. I've tried setting allowsNextDrawableTimeout to false which doesn't work; it returns a valid drawable after a second instead of nil. Setting displaySyncEnabled to false reduces the likelihood of this happening to around 50% from 90%+ but does not eliminate it. Setting maximumDrawableCount to 2 or 3 does not seem to make a difference. By dumping the resource IDs of the returned textures I've noticed something interesting: Before resizing, the layer seems to shuffle between 2 textures or at least 2 resource IDs, but after resizing it starts to create new textures for each returned drawable. Occasionally it seems to reuse a previous resource ID, but it does not seem to have anything to do with whether the method returns quickly or not. Why does this happen, and how can I fix it? Should I create a new CAMetalLayer when resizing the window instead of updating drawableSize?

I am interested in learning the Metal framework for rendering development. However, most of Apple’s official documentation uses Objective-C code. Therefore, I am seeking guidance on whether it is more advantageous for me to focus solely on learning Swift to gain proficiency in Metal.

I am making a framework in C++ using metal-cpp, basically a small game engine. I am also consequently using metal-cpp-extensions provided in LearnMetalCPP to make applications work. For one of my classes, I needed to add AppKit.hpp inside a public header file, so I moved it and its associate headers(NSApplication.hpp, NSMenu.hpp, etc.) from Project headers to Public in Build Phases' Headers, however, it started giving me the error "cast of C pointer type 'void *' to Objective-C pointer type 'Class' requires a bridged cast" at several points in the AppKit headers. They don't appear when AppKit and its associates are in the Project headers, or when they are in the Private headers and no headers import it. I imagined that disabling Objective-C ARC and Using __bridge casts outside of ARC in Build Settings would solve it, but it didn't budge. I imagined it wouldn't involve actively changing the headers would be the answer, but even if I try to put __bridge before the problematic casts, it didn't recognize __bridge. How do I solve this? And why is it only happening in Public and not Project headers?

Hello, Apple! This post is a bug report for Metal driver in MacOS Sequoia. I'm working on opensource game engine and one of my users reported a bug, on "MacOS Sequoia" + "AMD Radeon RX 6900 XT".  Engine crashes, when liking a compute pipeline, with following NSError: "Compiler encountered an internal error: I" Offended shader (depth aware blur): https://shader-playground.timjones.io/27565de40391f62f078c891077ba758c On my end, compiling same shader on M1 (Sonoma) or with offline compiler doesn't reproduce the issue. Post with bug-report on github: https://github.com/Try/OpenGothic/issues/712 Looking forward for your help and driver fix ;)

I'm trying to pass a buffer of float2 items from CPU to GPU. In the kernel, I can provide a parameter for the buffer: device const float2* values for example. How do I specify float2 as the type for the MTL::Buffer? I managed to get the code to work by "cheating" by defining a simple class that has the same data members as a float2, but there is probably a better way. class Coord_f { public: float x{0.0f}; float y{0.0f}; }; then using code to allocate like this: NS::TransferPtr(device->newBuffer(n_elements * sizeof(Coord_f), MTL::ResourceStorageModeManaged)) The headers for metal-cpp do not appear to define vector objects like float2, but I'm doubtless missing something. Thanks.

I am trying to use the SVGF denoiser to denoise my ray traced shadows (and also other textures later). I do get a smoothed image, but with wonky denoising. I need the depth-normal textures and motion textures for the SVGF and assume that these are badly filled in my case. However, neither in the above linked documentation nor in the WWDC19 video I find how they should be defined. I am looking to answers to: Is depth in red or alpha channel for the depth-normal texture? Are the normals in screen space? Is depth linear? Is it distance or z coordinate in view space? Or even logarithmically scaled or something else? Are the motion vectors supposed to be in pixels per frame? What is the orientation of the axis? Is y up or down? Are there are other restrictions on the formats? Also the linked code did not help me (I have not found any SVGF so far; also all the code is in Objective-C++, not Swift, but that's a different topic). So how should I fill these textures. Can someone point me to the documentation where these kinds of questions are answered?

What evidence exists that it's safe to call nextDrawable() on CAMetalLayer off the main thread? I have seen developers claiming that it's OK, but the official docs are silent on the topic. Attempting to do so with Strict Concurrency Checking set to Complete complains that CAMetalLayer is not @Sendable. I want to call it off the main thread since there doesn't seem to be any way to prevent it from blocking the UI for up to a second. I have read hints and allegations that this won't happen if you avoid asking for too many drawables, but that doesn't seem to be true 100% of the time in my experience. Supposing it is allowed, I wonder how races are handled such as when the layer's size is changed on the main thread, or if the layer is removed from the layer hierarchy.

Is there a working example of imageblock_slice with implicit layout somewhere? I get a compilation error when i write this: imageblock_slilce color_slice = img_blk.slice(frag->color); Error: No matching member function for call to 'slice' candidate template ignored: couldn't infer template argument 'E' candidate function template not viable: requires 2 arguments, but 1 was provided Too few template arguments for class template 'imageblock_slice' It seems the syntax has changed since the Imageblocks presentation https://developer.apple.com/videos/play/tech-talks/603/ I tried supplying the struct type of the image block between <> but it still does not work.