From 788f57cb52aa9b4e22ccf7786d036657797afaf0 Mon Sep 17 00:00:00 2001
From: Luke Street <luke.street@encounterpc.com>
Date: Wed, 16 Mar 2022 02:05:56 -0400
Subject: [PATCH] aurora: Use multiple staging buffers & map at end of frame

---
 aurora/lib/gfx/common.cpp | 43 +++++++++++++++++++++++++--------------
 aurora/lib/gfx/common.hpp |  1 +
 2 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/aurora/lib/gfx/common.cpp b/aurora/lib/gfx/common.cpp
index 5746b3000..3ccdee423 100644
--- a/aurora/lib/gfx/common.cpp
+++ b/aurora/lib/gfx/common.cpp
@@ -211,7 +211,7 @@ wgpu::Buffer g_uniformBuffer;
 wgpu::Buffer g_indexBuffer;
 wgpu::Buffer g_storageBuffer;
 size_t g_staticStorageLastSize = 0;
-static wgpu::Buffer g_stagingBuffer;
+static std::array<wgpu::Buffer, 2> g_stagingBuffers;
 
 static ShaderState g_state;
 static PipelineRef g_currentPipeline;
@@ -405,8 +405,11 @@ void initialize() {
                "Shared Index Buffer");
   createBuffer(g_storageBuffer, wgpu::BufferUsage::Storage | wgpu::BufferUsage::CopyDst, StorageBufferSize,
                "Shared Storage Buffer");
-  createBuffer(g_stagingBuffer, wgpu::BufferUsage::MapWrite | wgpu::BufferUsage::CopySrc, StagingBufferSize,
-               "Staging Buffer");
+  createBuffer(g_stagingBuffers[0], wgpu::BufferUsage::MapWrite | wgpu::BufferUsage::CopySrc, StagingBufferSize,
+               "Staging Buffer 1");
+  createBuffer(g_stagingBuffers[1], wgpu::BufferUsage::MapWrite | wgpu::BufferUsage::CopySrc, StagingBufferSize,
+               "Staging Buffer 2");
+  map_staging_buffer();
 
   g_state.moviePlayer = movie_player::construct_state();
   g_state.coloredQuad = colored_quad::construct_state();
@@ -429,31 +432,39 @@ void shutdown() {
   g_uniformBuffer = {};
   g_indexBuffer = {};
   g_storageBuffer = {};
-  g_stagingBuffer = {};
+  g_stagingBuffers.fill({});
 
   g_state = {};
 }
 
-void begin_frame() {
-  bool bufferMapped = false;
-  size_t bufferOffset = 0;
-  const auto mapBuffer = [&](ByteBuffer& buf, uint64_t size) {
-    buf = ByteBuffer{static_cast<u8*>(g_stagingBuffer.GetMappedRange(bufferOffset, size)), size};
-    bufferOffset += size;
-  };
-  g_stagingBuffer.MapAsync(
+static size_t currentStagingBuffer = 0;
+static bool bufferMapped = false;
+void map_staging_buffer() {
+  bufferMapped = false;
+  g_stagingBuffers[currentStagingBuffer].MapAsync(
       wgpu::MapMode::Write, 0, StagingBufferSize,
       [](WGPUBufferMapAsyncStatus status, void* userdata) {
-        if (status != WGPUBufferMapAsyncStatus_Success) {
+        if (status == WGPUBufferMapAsyncStatus_DestroyedBeforeCallback) {
+          return;
+        } else if (status != WGPUBufferMapAsyncStatus_Success) {
           Log.report(logvisor::Fatal, FMT_STRING("Buffer mapping failed: {}"), status);
           unreachable();
         }
         *static_cast<bool*>(userdata) = true;
       },
       &bufferMapped);
+}
+
+void begin_frame() {
   while (!bufferMapped) {
     g_device.Tick();
   }
+  size_t bufferOffset = 0;
+  auto& stagingBuf = g_stagingBuffers[currentStagingBuffer];
+  const auto mapBuffer = [&](ByteBuffer& buf, uint64_t size) {
+    buf = ByteBuffer{static_cast<u8*>(stagingBuf.GetMappedRange(bufferOffset, size)), size};
+    bufferOffset += size;
+  };
   mapBuffer(g_verts, VertexBufferSize);
   mapBuffer(g_uniforms, UniformBufferSize);
   mapBuffer(g_indices, IndexBufferSize);
@@ -465,16 +476,18 @@ void end_frame(const wgpu::CommandEncoder& cmd) {
   const auto writeBuffer = [&](ByteBuffer& buf, wgpu::Buffer& out, uint64_t size, std::string_view label) {
     const auto writeSize = buf.size(); // Only need to copy this many bytes
     if (writeSize > 0) {
-      cmd.CopyBufferToBuffer(g_stagingBuffer, bufferOffset, out, 0, writeSize);
+      cmd.CopyBufferToBuffer(g_stagingBuffers[currentStagingBuffer], bufferOffset, out, 0, writeSize);
       buf.clear();
     }
     bufferOffset += size;
   };
-  g_stagingBuffer.Unmap();
+  g_stagingBuffers[currentStagingBuffer].Unmap();
   writeBuffer(g_verts, g_vertexBuffer, VertexBufferSize, "Vertex");
   writeBuffer(g_uniforms, g_uniformBuffer, UniformBufferSize, "Uniform");
   writeBuffer(g_indices, g_indexBuffer, IndexBufferSize, "Index");
   writeBuffer(g_storage, g_storageBuffer, StorageBufferSize, "Storage");
+  currentStagingBuffer = (currentStagingBuffer + 1) % g_stagingBuffers.size();
+  map_staging_buffer();
 }
 
 void render(const wgpu::RenderPassEncoder& pass) {
diff --git a/aurora/lib/gfx/common.hpp b/aurora/lib/gfx/common.hpp
index c21c6c699..e990ed0d2 100644
--- a/aurora/lib/gfx/common.hpp
+++ b/aurora/lib/gfx/common.hpp
@@ -174,6 +174,7 @@ void shutdown();
 void begin_frame();
 void end_frame(const wgpu::CommandEncoder& cmd);
 void render(const wgpu::RenderPassEncoder& pass);
+void map_staging_buffer();
 
 Range push_verts(const uint8_t* data, size_t length);
 template <typename T>