resizable_shell.hpp

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#pragma once
 
// ResizableShell — plugin-window size constraints, aspect-ratio lock,
// and saved-size persistence.
//
// Plugin shells (VST3 IPlugViewContentScaleSupport, AU fit-in-window,
// CLAP clap_plugin_gui.adjust_size) all need the same three behaviors:
//  1. Clamp requested sizes to a min/max.
//  2. Optionally lock to an aspect ratio so resize handles move in step.
//  3. Round-trip the last accepted size across session reloads.
//
// This component owns the arithmetic. Format adapters delegate to it
// from their native resize callbacks and persist the last size blob
// alongside parameter state.
 
#include <cstdint>
#include <optional>
#include <span>
#include <vector>
 
namespace pulp::view {
 
struct Size {
    uint32_t width = 0;
    uint32_t height = 0;
    bool operator==(const Size& o) const {
        return width == o.width && height == o.height;
    }
};
 
struct ResizableShellConfig {
    Size min_size{200, 150};
    Size max_size{4096, 4096};
    Size initial_size{640, 480};
    double aspect_ratio = 0.0;
};
 
class ResizableShell {
public:
    explicit ResizableShell(ResizableShellConfig cfg = {})
        : cfg_(cfg), current_(negotiate_static_(cfg, cfg.initial_size)) {}

    Size negotiate(Size requested) const;

    Size apply(Size requested) {
        current_ = negotiate(requested);
        return current_;
    }
 
    Size current() const { return current_; }
    const ResizableShellConfig& config() const { return cfg_; }

    std::vector<uint8_t> serialize() const;

    bool deserialize(std::span<const uint8_t> blob);
 
private:
    // Free-function version of negotiate used by the ctor (negotiate()
    // depends on cfg_ which isn't initialized yet at member-init time).
    static Size negotiate_static_(const ResizableShellConfig& cfg, Size requested);
 
    ResizableShellConfig cfg_;
    Size current_;
};
 
}  // namespace pulp::view