From ec339b0282cdcc72e0acebbdb3653668f6ef4085 Mon Sep 17 00:00:00 2001
From: Ben Doherty <bendoherty@google.com>
Date: Thu, 8 Apr 2021 10:38:59 -0700
Subject: [PATCH] Fix texture swizzling crash with older Nvidia GPUs (#3779)

---
 filament/backend/src/metal/MetalContext.h  |  3 +++
 filament/backend/src/metal/MetalDriver.mm  | 19 ++++++++++++++-----
 filament/backend/src/metal/MetalHandles.mm |  5 ++++-
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/filament/backend/src/metal/MetalContext.h b/filament/backend/src/metal/MetalContext.h
index dad842f009..42163c99be 100644
--- a/filament/backend/src/metal/MetalContext.h
+++ b/filament/backend/src/metal/MetalContext.h
@@ -51,6 +51,9 @@ struct MetalContext {
     id<MTLCommandBuffer> pendingCommandBuffer = nullptr;
     id<MTLRenderCommandEncoder> currentRenderPassEncoder = nullptr;
 
+    // Supported features.
+    bool supportsTextureSwizzling = false;
+
     // Tracks resources used by command buffers.
     MetalResourceTracker resourceTracker;
 
diff --git a/filament/backend/src/metal/MetalDriver.mm b/filament/backend/src/metal/MetalDriver.mm
index b6706f8334..5b5375d5e8 100644
--- a/filament/backend/src/metal/MetalDriver.mm
+++ b/filament/backend/src/metal/MetalDriver.mm
@@ -78,6 +78,19 @@ MetalDriver::MetalDriver(backend::MetalPlatform* platform) noexcept
                   << [mContext->device.name cStringUsingEncoding:NSUTF8StringEncoding] << "'"
                   << utils::io::endl;
 
+    // In order to support texture swizzling, the GPU needs to support it and the system be running
+    // macOS 10.15+ / iOS 13+.
+    mContext->supportsTextureSwizzling = false;
+    if (@available(macOS 10.15, iOS 13, *)) {
+#if defined(IOS)
+        mContext->supportsTextureSwizzling =
+                [mContext->device supportsFeatureSet:MTLFeatureSet_iOS_GPUFamily1_v1];
+#else
+        mContext->supportsTextureSwizzling =
+                [mContext->device supportsFeatureSet:MTLFeatureSet_macOS_GPUFamily2_v1];
+#endif
+    }
+
     mContext->commandQueue = [mContext->device newCommandQueue];
     mContext->commandQueue.label = @"Filament";
     mContext->pipelineStateCache.setDevice(mContext->device);
@@ -588,11 +601,7 @@ bool MetalDriver::isTextureFormatSupported(TextureFormat format) {
 }
 
 bool MetalDriver::isTextureSwizzleSupported() {
-    if (@available(macOS 10.15, iOS 13, *)) {
-        return true;
-    } else {
-        return false;
-    }
+    return mContext->supportsTextureSwizzling;
 }
 
 bool MetalDriver::isTextureFormatMipmappable(TextureFormat format) {
diff --git a/filament/backend/src/metal/MetalHandles.mm b/filament/backend/src/metal/MetalHandles.mm
index 7f089257f9..0a799aec9c 100644
--- a/filament/backend/src/metal/MetalHandles.mm
+++ b/filament/backend/src/metal/MetalHandles.mm
@@ -502,7 +502,10 @@ MetalTexture::MetalTexture(MetalContext& context, SamplerType target, uint8_t le
             a == TextureSwizzle::CHANNEL_3;
     // If texture is nil, then it must be a SAMPLER_EXTERNAL texture. We'll ignore this case for now.
     // TODO: implement swizzling for external textures.
-    if (!isDefaultSwizzle && texture) {
+    if (!isDefaultSwizzle && texture && context.supportsTextureSwizzling) {
+        // Even though we've already checked context.supportsTextureSwizzling, we still need to
+        // guard these calls with @availability, otherwise the API usage will generate compiler
+        // warnings.
         if (@available(macOS 10.15, iOS 13, *)) {
             NSUInteger slices = texture.arrayLength;
             if (texture.textureType == MTLTextureTypeCube ||