feat(render): logical style metrics with a UI scale, so chrome has a consistent physical size

adapters/glfw/glfw_host.cpp

@@ -249,6 +249,12 @@ void Host::refresh_sizes() noexcept {
   fb_height_ = fh > 0 ? static_cast<u32>(fh) : 0u;
   if (ww > 0 && fw > 0) fb_scale_x_ = static_cast<f32>(fw) / static_cast<f32>(ww);
   if (wh > 0 && fh > 0) fb_scale_y_ = static_cast<f32>(fh) / static_cast<f32>(wh);
+  // The renderer draws its logical style metrics at this same ratio, so the chrome
+  // is the same physical size at any scale: one value states the display, and a
+  // 12 px label is 24 device px on the 2x panel both these sizes describe. Read here
+  // rather than in the frame loop because this is the one place the two sizes are,
+  // and re-read whenever the window moves to a display with another scale.
+  if (renderer_) renderer_->style().ui_scale = fb_scale_x_;
 }
 
 // ------------------------------------------------------------------ events

adapters/glfw/glfw_host.hpp

@@ -48,7 +48,10 @@ using FrameFn = std::function<void(plot::Plot&, f64 dt)>;
 /// `glfwGetWindowSize()` disagree. The host calls `begin_frame` with the
 /// framebuffer size and scales every pointer coordinate by the ratio
 /// `framebuffer / window`, so a gesture lands on the pixels the plot was laid out
-/// in. On an unscaled display the ratio is 1.0 and nothing changes.
+/// in. The same ratio states the display to the renderer
+/// (`Style::ui_scale`), which is what makes the chrome -- labels, strokes, paddings
+/// -- one physical size at any scale. On an unscaled display the ratio is 1.0 and
+/// nothing changes.
 ///
 /// Headless smoke mode, read once per `run()`:
 ///