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Rewrote ImVec2 subscripting to remove undefined behavior

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Brayden Lee 2025-12-20 00:51:28 -05:00
parent 760d5ec69a
commit e269a23a83
1 changed files with 11 additions and 3 deletions
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14
imgui.h
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@ -287,6 +287,7 @@ typedef int (*ImGuiInputTextCallback)(ImGuiInputTextCallbackData* data);
typedef void (*ImGuiSizeCallback)(ImGuiSizeCallbackData* data); // Callback function for ImGui::SetNextWindowSizeConstraints()
typedef void* (*ImGuiMemAllocFunc)(size_t sz, void* user_data); // Function signature for ImGui::SetAllocatorFunctions()
typedef void (*ImGuiMemFreeFunc)(void* ptr, void* user_data); // Function signature for ImGui::SetAllocatorFunctions()
namespace ImGui { [[noreturn]] inline void Unreachable(); }; // Function signature for ImGui::Unreachable()
// ImVec2: 2D vector used to store positions, sizes etc. [Compile-time configurable type]
// - This is a frequently used type in the API. Consider using IM_VEC2_CLASS_EXTRA to create implicit cast from/to our preferred type.
@ -297,8 +298,15 @@ struct ImVec2
float x, y;
constexpr ImVec2() : x(0.0f), y(0.0f) { }
constexpr ImVec2(float _x, float _y) : x(_x), y(_y) { }
float& operator[] (size_t idx) { IM_ASSERT(idx == 0 || idx == 1); return ((float*)(void*)(char*)this)[idx]; } // We very rarely use this [] operator, so the assert overhead is fine.
float operator[] (size_t idx) const { IM_ASSERT(idx == 0 || idx == 1); return ((const float*)(const void*)(const char*)this)[idx]; }
#define SUBSCRIPT_OPERATION \
switch (idx % 2) { \
case 0: return x; \
case 1: return y; \
default: ImGui::Unreachable(); /* Compiler hint: ensures optimization is taken and removes a false positive non-returning branch. */ \
};
float& operator[] (size_t idx) { SUBSCRIPT_OPERATION; }
float operator[] (size_t idx) const { SUBSCRIPT_OPERATION; }
#undef SUBSCRIPT_OPERATION
#ifdef IM_VEC2_CLASS_EXTRA
IM_VEC2_CLASS_EXTRA // Define additional constructors and implicit cast operators in imconfig.h to convert back and forth between your math types and ImVec2.
#endif
@ -2261,7 +2269,7 @@ IM_MSVC_RUNTIME_CHECKS_RESTORE
//-----------------------------------------------------------------------------
// If you are using C++>=23, use std::unreachable() in <utility>, and you may also define STD_UNREACHABLE_IS_AVAILABLE to substitute definitions.
// Code is from: https://en.cppreference.com/w/cpp/utility/unreachable.html
// Inclusion in the ImGUI namespace is chosen to avoid possible namespace collisions with stdlib >= 23.
// Inclusion in the ImGUI namespace is chosen to avoid possible namespace collisions.
//-----------------------------------------------------------------------------
namespace ImGui
{