Rotating text and icon demo for dear imgui

ImRotateDemo.cpp

#include "imgui_internal.h"

int rotation_start_index; 
void ImRotateStart() 
{ 
	rotation_start_index = ImGui::GetWindowDrawList()->VtxBuffer.Size; 
}

ImVec2 ImRotationCenter()
{
	ImVec2 l(FLT_MAX, FLT_MAX), u(-FLT_MAX, -FLT_MAX); // bounds

	const auto& buf = ImGui::GetWindowDrawList()->VtxBuffer;
	for (int i = rotation_start_index; i < buf.Size; i++)
		l = ImMin(l, buf[i].pos), u = ImMax(u, buf[i].pos);

	return ImVec2((l.x+u.x)/2, (l.y+u.y)/2); // or use _ClipRectStack?
}

ImVec2 operator-(const ImVec2& l, const ImVec2& r) { return{ l.x - r.x, l.y - r.y }; }

void ImRotateEnd(float rad, ImVec2 center = ImRotationCenter())
{
	float s=sin(rad), c=cos(rad);
	center = ImRotate(center, s, c) - center;

	auto& buf = ImGui::GetWindowDrawList()->VtxBuffer;
	for (int i = rotation_start_index; i < buf.Size; i++)
		buf[i].pos = ImRotate(buf[i].pos, s, c) - center;
}

//https://github.com/juliettef/IconFontCppHeaders/blob/master/IconsMaterialDesign_c.h
#include "IconsMaterialDesign_c.h"

void ImRotateDemo()
{
	ImRotateStart();
	ImGui::Text(__FUNCTION__);
	ImRotateEnd(0.5f * ImGui::GetTime());

	ImRotateStart(); ImGui::SameLine();
	ImGui::Text(ICON_MD_BRIGHTNESS_5);
	ImRotateEnd(0.005f*::GetTickCount()*!ImGui::IsItemHovered());
}