skinBatchInstance.h

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// SPDX-License-Identifier: Apache-2.0
// Copyright 2025-2026 Arnis Lektauers
//
// SkinBatchInstance — matrix palette manager for dynamic batching.
//
//
//
// Holds references to the GraphNode of each original mesh instance in a
// dynamic batch.  Each frame, updateMatrices() packs their world transforms
// into a flat float4x4 array (the "palette").  The renderer binds this
// palette at Metal buffer slot 6; the vertex shader indexes into it via
// per-vertex boneIndex to transform vertices on the GPU.
//
// DEVIATION: Standalone class, not extending SkinInstance (which is an
// empty stub).  Uses a Metal buffer instead of upstream's RGBA32F bone
// texture for simpler shader code and idiomatic Metal usage.
//
#pragma once
 
#include <cstring>
#include <vector>
 
#include "scene/graphNode.h"
 
namespace visutwin::canvas
{
    class SkinBatchInstance
    {
    public:
        explicit SkinBatchInstance(std::vector<GraphNode*> nodes);

        void updateMatrices();

        [[nodiscard]] const float* paletteData() const { return _palette.data(); }

        [[nodiscard]] size_t paletteSizeBytes() const { return _palette.size() * sizeof(float); }

        [[nodiscard]] int boneCount() const { return static_cast<int>(_nodes.size()); }
 
    private:
        std::vector<GraphNode*> _nodes;
        std::vector<float> _palette;  // N x 16 floats (float4x4 per bone)
    };
 
} // namespace visutwin::canvas