From e230e55ed4122b6cb0f502519e8c1d14254a996c Mon Sep 17 00:00:00 2001
From: assiduous <assiduous@diligentgraphics.com>
Date: Sun, 1 Oct 2023 20:46:22 -0700
Subject: [PATCH] Fixed staging buffers in WebGL (fix #412)

---
 Common/interface/StringTools.hpp              |  2 +-
 .../include/BufferGLImpl.hpp                  |  7 ++++++
 Graphics/GraphicsEngineOpenGL/include/pch.h   |  3 ++-
 .../GraphicsEngineOpenGL/src/BufferGLImpl.cpp | 22 ++++++++++++++++++-
 4 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/Common/interface/StringTools.hpp b/Common/interface/StringTools.hpp
index f2adcfd67..90dd3ea8c 100644
--- a/Common/interface/StringTools.hpp
+++ b/Common/interface/StringTools.hpp
@@ -205,7 +205,7 @@ inline size_t CountFloatNumberChars(const char* Str)
 /// For each chunk, calls the Handler.
 ///
 /// \note   This function is used to split long messages on Android to avoid
-///         trunction in logcat.
+///         truncation in logcat.
 template <typename IterType, typename HandlerType>
 void SplitLongString(IterType Start, IterType End, size_t MaxChunkLen, size_t NewLineSearchLen, HandlerType&& Handler)
 {
diff --git a/Graphics/GraphicsEngineOpenGL/include/BufferGLImpl.hpp b/Graphics/GraphicsEngineOpenGL/include/BufferGLImpl.hpp
index 87bb1ea88..0fbaa4e09 100644
--- a/Graphics/GraphicsEngineOpenGL/include/BufferGLImpl.hpp
+++ b/Graphics/GraphicsEngineOpenGL/include/BufferGLImpl.hpp
@@ -27,6 +27,8 @@
 
 #pragma once
 
+#include <vector>
+
 #include "EngineGLImplTraits.hpp"
 #include "BufferBase.hpp"
 #include "BufferViewGLImpl.hpp" // Required by BufferBase
@@ -92,6 +94,11 @@ class BufferGLImpl final : public BufferBase<EngineGLImplTraits>, public AsyncWr
     GLObjectWrappers::GLBufferObj m_GlBuffer;
     const Uint32                  m_BindTarget;
     const GLenum                  m_GLUsageHint;
+
+#if PLATFORM_EMSCRIPTEN
+    // Used for devices that don't support glMapBufferRange (currently, Emscripten)
+    std::vector<Uint8> m_MappedData;
+#endif
 };
 
 void BufferGLImpl::BufferMemoryBarrier(MEMORY_BARRIER RequiredBarriers, GLContextState& GLState)
diff --git a/Graphics/GraphicsEngineOpenGL/include/pch.h b/Graphics/GraphicsEngineOpenGL/include/pch.h
index c32ece35e..b94c07c7c 100644
--- a/Graphics/GraphicsEngineOpenGL/include/pch.h
+++ b/Graphics/GraphicsEngineOpenGL/include/pch.h
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2019-2022 Diligent Graphics LLC
+ *  Copyright 2019-2023 Diligent Graphics LLC
  *  Copyright 2015-2019 Egor Yusov
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
@@ -111,6 +111,7 @@
 
 #elif PLATFORM_EMSCRIPTEN
 
+#    include <webgl/webgl2.h>
 #    include <GLES3/gl32.h>
 #    include "GLStubsEmscripten.h"
 
diff --git a/Graphics/GraphicsEngineOpenGL/src/BufferGLImpl.cpp b/Graphics/GraphicsEngineOpenGL/src/BufferGLImpl.cpp
index 6595f6b86..259009dd0 100644
--- a/Graphics/GraphicsEngineOpenGL/src/BufferGLImpl.cpp
+++ b/Graphics/GraphicsEngineOpenGL/src/BufferGLImpl.cpp
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2019-2022 Diligent Graphics LLC
+ *  Copyright 2019-2023 Diligent Graphics LLC
  *  Copyright 2015-2019 Egor Yusov
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
@@ -277,6 +277,18 @@ void BufferGLImpl::MapRange(GLContextState& CtxState, MAP_TYPE MapType, Uint32 M
     constexpr bool ResetVAO = true;
     CtxState.BindBuffer(m_BindTarget, m_GlBuffer, ResetVAO);
 
+#if PLATFORM_EMSCRIPTEN
+    // Emscripten does not support mapping buffers for reading
+    if (MapType == MAP_READ)
+    {
+        m_MappedData.resize(static_cast<size_t>(Length));
+        glGetBufferSubData(m_BindTarget, StaticCast<GLintptr>(Offset), StaticCast<GLsizeiptr>(Length), m_MappedData.data());
+        CHECK_GL_ERROR("glGetBufferSubData() failed");
+        pMappedData = m_MappedData.data();
+        return;
+    }
+#endif
+
     // !!!WARNING!!! GL_MAP_UNSYNCHRONIZED_BIT is not the same thing as MAP_FLAG_DO_NOT_WAIT.
     // If GL_MAP_UNSYNCHRONIZED_BIT flag is set, OpenGL will not attempt to synchronize operations
     // on the buffer. This does not mean that map will fail if the buffer still in use. It is thus
@@ -328,6 +340,14 @@ void BufferGLImpl::MapRange(GLContextState& CtxState, MAP_TYPE MapType, Uint32 M
 
 void BufferGLImpl::Unmap(GLContextState& CtxState)
 {
+#if PLATFORM_EMSCRIPTEN
+    if (!m_MappedData.empty())
+    {
+        m_MappedData.clear();
+        return;
+    }
+#endif
+
     constexpr bool ResetVAO = true;
     CtxState.BindBuffer(m_BindTarget, m_GlBuffer, ResetVAO);
     auto Result = glUnmapBuffer(m_BindTarget);