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Fix bgfx allocation alignment #100

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Merged
ZivDero merged 1 commit into from
Aug 31, 2026
Merged

Fix bgfx allocation alignment #100

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2 changes: 2 additions & 0 deletions code/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -163,6 +163,8 @@ set(BGFX_ROOT "${CMAKE_SOURCE_DIR}/thirdparty/bgfx.cmake/bgfx")
set_source_files_properties("${CMAKE_CURRENT_SOURCE_DIR}/bgfxbackend.cpp" PROPERTIES
INCLUDE_DIRECTORIES
"${BGFX_ROOT}/include;${CMAKE_SOURCE_DIR}/thirdparty/bgfx.cmake/bx/include;${BGFX_ROOT}/examples/common/imgui"
COMPILE_DEFINITIONS
"BX_CONFIG_DEBUG=$<IF:$<CONFIG:Debug>,1,$<BOOL:${BX_CONFIG_DEBUG}>>"
COMPILE_OPTIONS "/Zc:preprocessor"
)

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28 changes: 28 additions & 0 deletions code/bgfxbackend.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,15 +15,18 @@
#include "dbgprint.h"
#include "except.h"

#include <bx/allocator.h>
#include <bgfx/bgfx.h>
#include <bgfx/embedded_shader.h>

#include <vs_ocornut_imgui.bin.h>
#include <fs_ocornut_imgui.bin.h>

#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <malloc.h>


static const bgfx::EmbeddedShader _EmbeddedShaders[] = {
Expand Down Expand Up @@ -119,6 +122,30 @@ class BackendCallback : public bgfx::CallbackI
static BackendCallback _Callback;


// bgfx contains cache-line-aligned render records but requests their backing arrays with
// the allocator's default alignment. The Win32 CRT only guarantees eight-byte alignment,
// which is insufficient when clang-cl copies those records with aligned SSE instructions.
class BackendAllocator : public bx::AllocatorI
{
public:
virtual ~BackendAllocator(void) override {}

virtual void * realloc(void * ptr, size_t size, size_t alignment, const char *, uint32_t) override
{
if (size == 0) {
_aligned_free(ptr);
return(NULL);
}

const size_t cachelinealignment = BX_CACHE_LINE_SIZE;
alignment = std::max(alignment, cachelinealignment);
return(_aligned_realloc(ptr, size, alignment));
}
};

static BackendAllocator _Allocator;


/// <summary>
/// Builds the table that widens a 565 pixel to the 32 bit color the fallback path uploads.
/// </summary>
Expand Down Expand Up @@ -273,6 +300,7 @@ bool Backend_Init(HWND window, int windowwidth, int windowheight, BackendRendere
init.resolution.height = (uint32_t)windowheight;
init.resolution.reset = _ResetFlags;
init.callback = &_Callback;
init.allocator = &_Allocator;

switch (renderer) {
case BACKEND_RENDERER_D3D11:
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