From ce3e5f74e8a6fe798c5e593de7abd1b95bc158ae Mon Sep 17 00:00:00 2001
From: Ben Doherty <bendoherty@google.com>
Date: Wed, 25 Aug 2021 09:48:07 -0700
Subject: [PATCH] Fix Metal STREAM buffers (#4543)

---
 filament/backend/src/metal/MetalBuffer.h  |  5 +++--
 filament/backend/src/metal/MetalBuffer.mm | 12 ++++++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/filament/backend/src/metal/MetalBuffer.h b/filament/backend/src/metal/MetalBuffer.h
index f4c69076b2..1cb63e5204 100644
--- a/filament/backend/src/metal/MetalBuffer.h
+++ b/filament/backend/src/metal/MetalBuffer.h
@@ -62,7 +62,7 @@ public:
      * Returns the offset into the buffer returned by getGpuBufferForDraw. This is always 0 for
      * non-STREAM buffers.
      */
-    size_t getGpuBufferStreamOffset() noexcept { return mCurrentStreamOffset; }
+    size_t getGpuBufferStreamOffset() noexcept { return mCurrentStreamStart; }
 
     void* getCpuBuffer() const noexcept { return mCpuBuffer; }
 
@@ -85,7 +85,8 @@ private:
 
     BufferUsage mUsage;
     size_t mBufferSize = 0;
-    size_t mCurrentStreamOffset = 0;
+    size_t mCurrentStreamStart = 0;
+    size_t mCurrentStreamEnd = 0;
     const MetalBufferPoolEntry* mBufferPoolEntry = nullptr;
     void* mCpuBuffer = nullptr;
     MetalContext& mContext;
diff --git a/filament/backend/src/metal/MetalBuffer.mm b/filament/backend/src/metal/MetalBuffer.mm
index 743c52b982..f93aebbef1 100644
--- a/filament/backend/src/metal/MetalBuffer.mm
+++ b/filament/backend/src/metal/MetalBuffer.mm
@@ -93,9 +93,13 @@ void MetalBuffer::copyIntoStreamBuffer(void* src, size_t size) {
     assert_invariant(size <= mBufferSize);
     assert_invariant(!mCpuBuffer);
 
-    if (mCurrentStreamOffset + size > mBufferSize) {
+    mCurrentStreamStart = mCurrentStreamEnd;
+    mCurrentStreamEnd += size;
+
+    if (mCurrentStreamEnd > mBufferSize) {
         // Allocate a new buffer and reset the stream offset.
-        mCurrentStreamOffset = 0;
+        mCurrentStreamStart = 0;
+        mCurrentStreamEnd = size;
 
         if (mBufferPoolEntry) { mContext.bufferPool->releaseBuffer(mBufferPoolEntry); }
         mBufferPoolEntry = mContext.bufferPool->acquireBuffer(mBufferSize);
@@ -106,7 +110,7 @@ void MetalBuffer::copyIntoStreamBuffer(void* src, size_t size) {
         mBufferPoolEntry = mContext.bufferPool->acquireBuffer(mBufferSize);
     }
 
-    memcpy(static_cast<uint8_t*>(mBufferPoolEntry->buffer.contents) + mCurrentStreamOffset, src, size);
+    memcpy(static_cast<uint8_t*>(mBufferPoolEntry->buffer.contents) + mCurrentStreamStart, src, size);
 }
 
 id<MTLBuffer> MetalBuffer::getGpuBufferForDraw(id<MTLCommandBuffer> cmdBuffer) noexcept {
@@ -160,7 +164,7 @@ void MetalBuffer::bindBuffers(id<MTLCommandBuffer> cmdBuffer, id<MTLRenderComman
             continue;
         }
         metalBuffers[b] = gpuBuffer;
-        metalOffsets[b] = offsets[b] + buffer->mCurrentStreamOffset;
+        metalOffsets[b] = offsets[b] + buffer->mCurrentStreamStart;
     }
 
     if (stages & Stage::VERTEX) {