Replace rather than update Metal buffers

src/mbgl/mtl/buffer_resource.cpp

@@ -91,8 +91,29 @@ void BufferResource::update(const void* data, std::size_t updateSize, std::size_
 
     if (updateSize > 0) {
         if (buffer) {
-            if (auto* content = static_cast<uint8_t*>(buffer->contents())) {
-                std::memcpy(content + offset, data, updateSize);
+            if (auto* const content = static_cast<uint8_t*>(buffer->contents())) {
+                // Until we can be sure that the buffer is not still in use to render the
+                // previous frame, replace it with a new buffer instead of updating it.
+                auto& device = context.getBackend().getDevice();
+
+                const bool updateIsEntireBuffer = (offset == 0 && updateSize == size);
+                const auto copySource = updateIsEntireBuffer ? data : content;
+                auto newBuffer = NS::TransferPtr(device->newBuffer(copySource, size, usage));
+
+                assert(newBuffer);
+                if (newBuffer) {
+                    buffer = std::move(newBuffer);
+
+                    // Apply the update to the new buffer, if necessary
+                    if (!updateIsEntireBuffer) {
+                        auto* const newContent = static_cast<uint8_t*>(buffer->contents());
+
+                        assert(newContent);
+                        if (newContent) {
+                            std::memcpy(newContent + offset, data, updateSize);
+                        }
+                    }
+                }
             }
         } else {
             std::memcpy(raw.data() + offset, data, updateSize);

src/mbgl/mtl/drawable.cpp

@@ -499,6 +499,8 @@ void Drawable::upload(gfx::UploadPass& uploadPass_) {
     }
 
     if (impl->indexes->getDirty()) {
+        // Create or update a buffer for the index data.  We don't update any
+        // existing buffer because it may still be in use by the previous frame.
         auto indexBufferResource{uploadPass.createIndexBufferResource(
             impl->indexes->data(), impl->indexes->bytes(), usage, /*persistent=*/false)};
         auto indexBuffer = std::make_unique<gfx::IndexBuffer>(impl->indexes->elements(),