auto_exposure_pass.h

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#pragma once
 
#include <engine/rendering/gpu_program.h>
#include <graphics/render_view.h>
#include <bgfx/bgfx.h>
#include <cstdint>
 
namespace unravel
{
 
enum class exposure_metering_mode : std::uint8_t
{
    average = 0,
    center_weighted = 1,
    spot = 2,
};
 
class auto_exposure_pass
{
public:
    auto_exposure_pass() = default;
    ~auto_exposure_pass()
    {
        shutdown();
    }
    struct settings
    {
        float min_ev = -4.0f;
        float max_ev = 0.0f;
        float compensation = 0.0f;
        float adaptation_speed_up = 3.0f;
        float adaptation_speed_down = 1.0f;
        float low_percentile = 0.50f;
        float high_percentile = 0.95f;
        exposure_metering_mode metering_mode = exposure_metering_mode::center_weighted;
        float metering_area = 0.7f;
    };
 
    struct run_params
    {
        gfx::frame_buffer::ptr input;
        settings config{};
        float delta_time = 0.0f;
    };
 
    auto init(rtti::context& ctx) -> bool;
    auto shutdown() -> int32_t;
    void run(gfx::render_view& rview, const run_params& params);
 
    auto get_exposure_texture(gfx::render_view& rview) const -> gfx::texture::ptr;
 
    void release_resources(gfx::render_view& rview);
 
private:
    static constexpr float min_log_lum = -10.0f;
    static constexpr float max_log_lum = 20.0f;
    static constexpr int histogram_bins = 256;
    static constexpr std::uint32_t max_metering_dim = 512;
 
    void ensure_resources(gfx::render_view& rview);
    void run_histogram(gfx::render_view& rview, const settings& config, const gfx::frame_buffer::ptr& input);
    void run_average(gfx::render_view& rview, const settings& config, float dt);
 
    struct histogram_program : uniforms_cache
    {
        gpu_program::ptr program;
        gfx::program::uniform_ptr s_hdr_input;
        gfx::program::uniform_ptr u_histogram_params;
        gfx::program::uniform_ptr u_metering_params;
 
        void cache_uniforms()
        {
            cache_uniform(program.get(), s_hdr_input, "s_hdr_input", gfx::uniform_type::Sampler);
            cache_uniform(program.get(), u_histogram_params, "u_histogram_params", gfx::uniform_type::Vec4);
            cache_uniform(program.get(), u_metering_params, "u_metering_params", gfx::uniform_type::Vec4);
        }
    } histogram_program_;
 
    struct average_program : uniforms_cache
    {
        gpu_program::ptr program;
        gfx::program::uniform_ptr u_average_params0;
        gfx::program::uniform_ptr u_average_params1;
        gfx::program::uniform_ptr u_average_params2;
 
        void cache_uniforms()
        {
            cache_uniform(program.get(), u_average_params0, "u_average_params0", gfx::uniform_type::Vec4);
            cache_uniform(program.get(), u_average_params1, "u_average_params1", gfx::uniform_type::Vec4);
            cache_uniform(program.get(), u_average_params2, "u_average_params2", gfx::uniform_type::Vec4);
        }
    } average_program_;
 
    bgfx::DynamicIndexBufferHandle histogram_buffer_ = BGFX_INVALID_HANDLE;
};
 
} // namespace unravel