Fix Graphite/Metal GradientBlend on the iOS simulator + shader-error diagnostic API (#4555) by ramezgerges · Pull Request #4586 · mono/SkiaSharp

ramezgerges · 2026-07-30T00:53:29Z

Description

Fixes #4555 (Graphite/Metal GradientBlend cell returning null Recorder.Snap() only on the iOS simulator) and adds the C API surface used to diagnose it.

Two commits, two roles:

SKGraphiteContext shader-error-handler overloads — wraps the new sk_graphite_context_options.fShaderErrorHandler C API. New backwards-compatible CreateDawn/CreateMetal/CreateVulkan overloads take an SKGraphiteShaderErrorHandlerDelegate; delegate is pinned for the Context's lifetime and freed in DisposeNative after the native context tears down its handler pointer. The proxy never throws across the FFI boundary — a bad handler cannot crash Skia's shader-compile path.
Fix Graphite/Metal GradientBlend on the iOS simulator — bumps the submodule to pick up the two Skia-side fixes: PSO-creation failures now routed through ShaderErrorHandler, and framebuffer fetch disabled under TARGET_OS_SIMULATOR. Drops the simulator-only null-Snap() skip seam from GraphiteMetalRenderer (a null Snap is again a hard failure everywhere, so regressions can't hide behind the skip) and adds the newly-passing graphite-metal.ios/GradientBlend.png golden.

Related issues

Fixes #4555

Required skia PR

Requires mono/skia#308

Areas affected

Changes

Public API

ABI-stable additive changes only.

// new delegate
public delegate void SKGraphiteShaderErrorHandlerDelegate(string shader, string errors, bool shaderWasCached);

// new overloads on SKGraphiteContext
public static SKGraphiteContext CreateDawn(
    SKGraphiteDawnBackendContext backendContext,
    SKGraphiteContextOptions options,
    SKGraphiteShaderErrorHandlerDelegate shaderErrorHandler);

public static SKGraphiteContext CreateMetal(
    SKGraphiteMtlBackendContext backendContext,
    SKGraphiteContextOptions options,
    SKGraphiteShaderErrorHandlerDelegate shaderErrorHandler);

public static SKGraphiteContext CreateVulkan(
    SKGraphiteVkBackendContext backendContext,
    SKGraphiteContextOptions options,
    SKGraphiteShaderErrorHandlerDelegate shaderErrorHandler);

Behavior

Graphite/Metal on iOS/tvOS simulator: GradientBlend (and any other draw needing a dst read with a non-coefficient blend — Multiply, Screen, Overlay, …) now renders correctly instead of returning null from Recorder.Snap(). Real Apple devices and macOS unchanged.
The simulator-only null-Snap() skip in GraphiteMetalRenderer is removed — regressions to this class of bug now fail loudly.
Callers who install a shader-error handler now also receive Metal PSO-creation failures (previously invisible outside SkDebugf).

Testing

Full SkiaSharp.Tests.Devices run on iPhone 16 / iOS 26.1 simulator (arm64): 1219 total, 0 failed, 1138 succeeded, 81 skipped. GradientBlend cell rendering and matching its committed graphite-metal.ios golden.

GraphiteVkContextAcceptsShaderErrorHandler smoke test on Linux/Lavapipe (Vulkan): passes — proves no double-free / no EntryPointNotFoundException on Context teardown after installing a handler. The Metal simulator path itself needs an Apple host to reproduce, which is what the Devices-tests run above covered.

Checklist

Tests added or updated (if omitted, explain why above)
Changes above lists all public API and behavioral changes (or "None.")
New/changed public API? Filed a docs issue in mono/SkiaSharp-API-docs so reference docs can be written later
Native change? Companion mono/skia PR linked above and bindings regenerated

github-actions · 2026-07-30T00:53:37Z

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Remove the source when you're done:

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#4555 was broadened to cover all three Metal failures because they share a root cause: no CI host has a real Metal device. That was wrong for tracking. #4586 carries 'Fixes #4555' and addresses only the iOS simulator's gradient pipeline, so merging it would have silently closed the macOS shutdown hang and the Mac Catalyst GPU-family gap along with it. #4555 is back to its original scope. The other two are now #4598 (macOS virtualized Metal hangs the test host on shutdown, killing the whole leg) and #4599 (Mac Catalyst reports no MTLGPUFamily that Ganesh or Graphite accepts). Each has its own cause and its own likely fix -- an Apple Silicon pool for the first, possibly a probe change for the second -- so each closes on its own. Repointed the opt-out comments and the policy doc at whichever issue explains that leg, and updated the #4591 umbrella table. The iOS leg cites both #4598 and #4555, because the simulator has the shutdown hang *and* the gradient bug.

mattleibow · 2026-07-31T06:18:24Z

/azp run

azure-pipelines · 2026-07-31T06:18:31Z

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ramezgerges · 2026-08-03T17:19:16Z

Rebased onto the current main and resolved the GraphiteMetalRenderer.cs conflict (kept the version that removes the null-Snap workaround, which is exactly what this PR fixes). The two failed /azp run attempts happened while I was force-pushing; the branch is stable now.

azure-pipelines · 2026-08-03T18:10:40Z

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Copilot

Pull request overview

This PR fixes a Graphite/Metal iOS-simulator rendering failure (null Recorder.Snap() in the GradientBlend scene) and introduces a managed shader-error diagnostic hook by wiring a new native fShaderErrorHandler option through to SKGraphiteContext creation.

Changes:

Adds SKGraphiteShaderErrorHandlerDelegate and new CreateDawn/CreateMetal/CreateVulkan overloads that accept a shader-error handler, with lifetime management via pinned delegates and a native bridge handle.
Removes the simulator-specific null-Snap() special-casing in the Graphite/Metal visual renderer so regressions fail consistently across hosts.
Adds a Vulkan smoke test ensuring installing a shader-error handler does not break context teardown and basic submission.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/VulkanTests/GraphiteVkBackendContextTest.cs	Adds a Vulkan smoke test for the new shader-error handler overload and lifetime/teardown behavior.
tests/Tests/SkiaSharp/Visual/Renderers/GraphiteMetalRenderer.cs	Makes `Recorder.Snap()` null a hard failure on all hosts (including simulator) now that the underlying issue is fixed.
binding/SkiaSharp/SkiaApi.generated.cs	Adds new P/Invoke surface and struct field for `sk_graphite_shader_error_handler_t` and `SKGraphiteContextOptions.fShaderErrorHandler`.
binding/SkiaSharp/Gpu/Graphite/SKGraphiteContext.cs	Adds handler-overload factories and pins/tears down managed + native handler bridge resources.
binding/SkiaSharp/DelegateProxies.cs	Adds the managed callback proxy implementation for shader-error handler invocations.
binding/SkiaSharp.Skottie/SkottieApi.generated.cs	Regenerates typedefs to include the new Graphite shader-error handler type alias.
binding/SkiaSharp.SceneGraph/SceneGraphApi.generated.cs	Regenerates typedefs to include the new Graphite shader-error handler type alias.
binding/SkiaSharp.Resources/ResourcesApi.generated.cs	Regenerates typedefs to include the new Graphite shader-error handler type alias.

mattleibow

Requesting changes: the shader-handler test does not verify callback delivery, and the new backend-specific test setup should be consolidated with the existing Graphite backend harness so future Graphite scenarios can run consistently across Vulkan, Metal, and Dawn.

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github-actions · 2026-08-04T03:25:38Z

📦 Artifact size report

Packages from this PR (build 1539617) vs the latest nightly baseline 4.151.0-nightly.124 (observed 2026-08-04).

Total .nupkg size: 569.4 MB → 569.1 MB (−296.6 KB, -0.1%)

Packages

⚠️ marks growth over 500.0 KB or 2%. Changes under 50.0 KB are treated as noise.

Package	baseline	this PR	Δ	Δ%
`SkiaSharp.NativeAssets.WinUI`	109.1 MB	108.6 MB	🟢 −451.5 KB	-0.4%
`SkiaSharp.NativeAssets.WebAssembly`	69.6 MB	69.6 MB	🔴 +67.5 KB	+0.1%

+38 package(s) unchanged (< 50.0 KB).

Per-file changes

`SkiaSharp.NativeAssets.WebAssembly`

File	Size
🧬 `wasm 5.0.6/mt · libSkiaSharp.a` (`buildTransitive/netstandard1.0/libSkiaSharp.a/5.0.6/mt/libSkiaSharp.a`)	17.9 MB → 17.9 MB (🔴 +1.5 KB)
🧬 `wasm 5.0.6/st,simd · libSkiaSharp.a` (`buildTransitive/netstandard1.0/libSkiaSharp.a/5.0.6/st,simd/libSkiaSharp.a`)	18.2 MB → 18.2 MB (🔴 +1.5 KB)
🧬 `wasm 5.0.6/mt,simd · libSkiaSharp.a` (`buildTransitive/netstandard1.0/libSkiaSharp.a/5.0.6/mt,simd/libSkiaSharp.a`)	18.2 MB → 18.2 MB (🔴 +1.5 KB)
🧬 `wasm 5.0.6/st · libSkiaSharp.a` (`buildTransitive/netstandard1.0/libSkiaSharp.a/5.0.6/st/libSkiaSharp.a`)	17.9 MB → 17.9 MB (🔴 +1.5 KB)
🧬 `wasm 3.1.56/mt · libSkiaSharp.a` (`buildTransitive/netstandard1.0/libSkiaSharp.a/3.1.56/mt/libSkiaSharp.a`)	17.7 MB → 17.7 MB (🔴 +1.5 KB)
🧬 `wasm 3.1.56/st · libSkiaSharp.a` (`buildTransitive/netstandard1.0/libSkiaSharp.a/3.1.56/st/libSkiaSharp.a`)	17.8 MB → 17.8 MB (🔴 +1.5 KB)
🧬 `wasm 3.1.56/mt,simd · libSkiaSharp.a` (`buildTransitive/netstandard1.0/libSkiaSharp.a/3.1.56/mt,simd/libSkiaSharp.a`)	18.0 MB → 18.0 MB (🔴 +1.5 KB)
🧬 `wasm 3.1.56/st,simd · libSkiaSharp.a` (`buildTransitive/netstandard1.0/libSkiaSharp.a/3.1.56/st,simd/libSkiaSharp.a`)	18.0 MB → 18.0 MB (🔴 +1.5 KB)

`SkiaSharp.NativeAssets.WinUI`

File	Size
`runtimes/win-x64/native/libGLESv2.pdb`	66.6 MB → 66.5 MB (🟢 −144.0 KB)
`runtimes/win-arm64/native/libGLESv2.pdb`	64.5 MB → 64.4 MB (🟢 −80.0 KB)
`runtimes/win-x86/native/libGLESv2.pdb`	67.3 MB → 67.2 MB (🟢 −80.0 KB)

_{Informational only — this never blocks the PR. Native binaries are labelled by os/arch.}

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Wraps the new sk_graphite_context_options.fShaderErrorHandler C API so managed callers can capture Graphite shader compile failures. The motivating case is the Metal iOS simulator gradient scene where Recorder.Snap() silently returns null with no diagnostic — Skia's default handler prints via SkDebugf + asserts, which is invisible in shipping apps on Apple platforms. * new CreateDawn/CreateMetal/CreateVulkan overloads taking SKGraphiteShaderErrorHandlerDelegate (backwards-compatible additions, no signature changes) * SKGraphiteShaderErrorHandlerDelegate proxy in DelegateProxies never throws across the FFI boundary — a bad handler cannot crash Skia's shader-compile path * GCHandle pinned for the Context's lifetime, freed in DisposeNative after the native context tears down its internal handler pointer Includes GraphiteVkContextAcceptsShaderErrorHandler smoke test that proves the wiring survives Context create + trivial draw + dispose on Vulkan (Lavapipe compiles cleanly so the callback does not fire — the important assertion is no double-free / no EntryPointNotFound on teardown). The Metal simulator failure path requires an iOS host to reproduce and is out of scope for CI. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Root cause (diagnosed with the fShaderErrorHandler hook from this branch, plus PSO-failure forwarding added to it): Graphite's MtlCaps enabled framebuffer fetch for every Apple-family GPU and Caps::getDstReadStrategy() then always used it for dst reads. The iOS simulator advertises an Apple GPU family but cannot read a render target from a fragment shader — the MSL compiles, but newRenderPipelineStateWithDescriptor fails with CompilerError Code=2 "reading from a rendertarget is not supported" — so the Multiply-blend draw in GradientBlend (the only matrix scene needing a dst read) nulled its pipeline and Recorder.Snap() returned null. Ganesh/Metal never uses framebuffer fetch and real devices/macOS support it, which is why only this one cell failed. Submodule changes (mono/skia dev/issue-4555-graphite-shader-error-handler): * Metal PSO-creation failures are now reported through the ShaderErrorHandler (previously SkDebugf-only, invisible on iOS) * framebuffer fetch is disabled under TARGET_OS_SIMULATOR; dst reads fall back to DstReadStrategy::kTextureCopy there Test harness: * remove the simulator-only null-Snap() skip seam from GraphiteMetalRenderer — a null Snap() is a hard failure everywhere again, so regressions can no longer hide behind the skip * seed the graphite-metal.ios/GradientBlend golden (rendered on an iPhone 16 / iOS 26.1 simulator; pixel-identical to the graphite-metal.macos golden) Verified on the iOS simulator: full SkiaSharp.Tests.Devices run is green (1219 total, 0 failed, 1138 succeeded, 81 skipped), with the GradientBlend cell rendering and matching its golden. Fixes mono#4555. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

github-project-automation Bot added this to SkiaSharp Backlog Jul 30, 2026

ramezgerges mentioned this pull request Jul 30, 2026

Graphite shader-error handler + fix iOS-simulator dst read (mono/SkiaSharp#4555) mono/skia#308

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dotnet-policy-service Bot added the community ✨ label Jul 30, 2026

ramezgerges force-pushed the dev/issue-4555-graphite-shader-error-handler branch from 0b92317 to 9ab7523 Compare August 3, 2026 17:18

ramezgerges force-pushed the dev/issue-4555-graphite-shader-error-handler branch from 9ab7523 to a12b2b3 Compare August 3, 2026 17:41

mattleibow requested a review from Copilot August 3, 2026 18:39

Copilot started reviewing on behalf of mattleibow August 3, 2026 18:40 View session

Copilot AI reviewed Aug 3, 2026

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Comment thread binding/SkiaSharp/DelegateProxies.cs

Comment thread binding/SkiaSharp/Gpu/Graphite/SKGraphiteContext.cs Outdated

Comment thread binding/SkiaSharp/SkiaApi.generated.cs Outdated

mattleibow requested changes Aug 3, 2026

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Comment thread tests/VulkanTests/GraphiteVkBackendContextTest.cs Outdated

Comment thread tests/VulkanTests/GraphiteVkBackendContextTest.cs Outdated

github-project-automation Bot moved this to Changes Requested in SkiaSharp Backlog Aug 3, 2026

ramezgerges force-pushed the dev/issue-4555-graphite-shader-error-handler branch from a12b2b3 to 077354b Compare August 4, 2026 16:54

ramezgerges and others added 2 commits September 14, 2026 11:10

ramezgerges force-pushed the dev/issue-4555-graphite-shader-error-handler branch from 077354b to 71c6d22 Compare September 14, 2026 15:16

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`SkiaSharp.NativeAssets.WebAssembly`

`SkiaSharp.NativeAssets.WinUI`