UnrealImGui/Source/ImGui/Private/ImGuiDrawData.h

// Distributed under the MIT License (MIT) (see accompanying LICENSE file)

#pragma once

#include "ImGuiInteroperability.h"
#include "VersionCompatibility.h"

#include <Rendering/RenderingCommon.h>

#include <imgui.h>


// ImGui draw command data transformed for Slate.
struct FImGuiDrawCommand
{
	uint32 NumElements;
	FSlateRect ClippingRect;
	TextureIndex TextureId;
};

// Wraps raw ImGui draw list data in utilities that transform them for Slate.
class FImGuiDrawList
{
public:

	// Get the number of draw commands in this list.
	FORCEINLINE int NumCommands() const { return ImGuiCommandBuffer.Size; }

	// Get the draw command by number.
	// @param CommandNb - Number of draw command
	// @param Transform - Transform to apply to clipping rectangle
	// @returns Draw command data
	FImGuiDrawCommand GetCommand(int CommandNb, const FTransform2D& Transform) const
	{
		const ImDrawCmd& ImGuiCommand = ImGuiCommandBuffer[CommandNb];
		return { ImGuiCommand.ElemCount, TransformRect(Transform, ImGuiInterops::ToSlateRect(ImGuiCommand.ClipRect)),
			ImGuiInterops::ToTextureIndex(ImGuiCommand.TextureId) };
	}

#if ENGINE_COMPATIBILITY_LEGACY_CLIPPING_API
	// Transform and copy vertex data to target buffer (old data in the target buffer are replaced).
	// @param OutVertexBuffer - Destination buffer
	// @param Transform - Transform to apply to all vertices
	// @param VertexClippingRect - Clipping rectangle for transformed Slate vertices
	void CopyVertexData(TArray<FSlateVertex>& OutVertexBuffer, const FTransform2D& Transform, const FSlateRotatedRect& VertexClippingRect) const;
#else
	// Transform and copy vertex data to target buffer (old data in the target buffer are replaced).
	// @param OutVertexBuffer - Destination buffer
	// @param Transform - Transform to apply to all vertices
	void CopyVertexData(TArray<FSlateVertex>& OutVertexBuffer, const FTransform2D& Transform) const;
#endif // ENGINE_COMPATIBILITY_LEGACY_CLIPPING_API

	// Transform and copy index data to target buffer (old data in the target buffer are replaced).
	// Internal index buffer contains enough data to match the sum of NumElements from all draw commands.
	// @param OutIndexBuffer - Destination buffer
	// @param StartIndex - Start copying source data starting from this index
	// @param NumElements - How many elements we want to copy
	void CopyIndexData(TArray<SlateIndex>& OutIndexBuffer, const int32 StartIndex, const int32 NumElements) const;

	// Transfers data from ImGui source list to this object. Leaves source cleared.
	void TransferDrawData(ImDrawList& Src);

private:

	ImVector<ImDrawCmd> ImGuiCommandBuffer;
	ImVector<ImDrawIdx> ImGuiIndexBuffer;
	ImVector<ImDrawVert> ImGuiVertexBuffer;
};