pixel_density.hpp

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#pragma once


#include <planet/affine/extents2d.hpp>
#include <planet/sdl/sdl.hpp>


namespace planet::sdl {

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    inline affine::extents2d pixel_density(SDL_Window *const window) noexcept

The number of drawable pixels per logical point for the display window is on — > 1 on a HiDPI/Retina display and 1 otherwise. Mouse events and display extents arrive in logical points whereas the swapchain works in drawable pixels, so multiply the former by this to reach the latter.

SDL reports a single density, so both axes carry the same value here. Returning affine::extents2d (the aspect-ratio vocabulary used elsewhere) leaves room for an anisotropic density without touching call sites. Falls back to {1, 1} for a null window or when SDL cannot report a density, so callers can multiply unconditionally.

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    {
        float const density = window ? SDL_GetWindowPixelDensity(window) : 0.0f;
        float const scale = density > 0.0f ? density : 1.0f;
        return {scale, scale};
    }

    inline affine::extents2d pixel_density(SDL_WindowID const window_id) noexcept

Look the window up by id first. An unknown id yields {1, 1}.

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    {
        return pixel_density(SDL_GetWindowFromID(window_id));
    }


}