add a flag to override DPI, so we can tune on mac

docs/INSTRUCTIONS.md

@@ -15,7 +15,11 @@ Grab a pre-built binary release -- updated every Sunday, announced at
   https://github.com/dabreegster/abstreet/releases/download/v0.1.19/abstreet_windows_v0_1_19.zip
 - Mac:
   https://github.com/dabreegster/abstreet/releases/download/v0.1.19/abstreet_mac_v0_1_19.zip
-  - The minimap may be missing, depending on your monitor's DPI.
+  - The minimap may be missing, depending on your monitor's DPI. If so, modify
+    the `play_abstreet.sh` script to pass `--hidpi_factor=2.0` and experiment
+    with different values. If you have to do this, please
+    [file an issue](https://github.com/dabreegster/abstreet/issues) and let me
+    know, so I can figure out why `glutin` misreports this.
 - Linux:
   https://github.com/dabreegster/abstreet/releases/download/v0.1.19/abstreet_linux_v0_1_19.zip
   - The binary might not work on your flavor of Linux; let me know

ezgui/src/runner.rs

@@ -181,6 +181,7 @@ pub struct Settings {
     initial_dims: (f64, f64),
     profiling_enabled: bool,
     default_font_size: usize,
+    override_hidpi_factor: Option<f64>,
 }
 
 impl Settings {
@@ -190,6 +191,7 @@ impl Settings {
             initial_dims,
             profiling_enabled: false,
             default_font_size: 30,
+            override_hidpi_factor: None,
         }
     }
 
@@ -201,6 +203,10 @@ impl Settings {
     pub fn default_font_size(&mut self, size: usize) {
         self.default_font_size = size;
     }
+
+    pub fn override_hidpi_factor(&mut self, override_hidpi_factor: f64) {
+        self.override_hidpi_factor = Some(override_hidpi_factor);
+    }
 }
 
 pub fn run<G: GUI, F: FnOnce(&mut EventCtx) -> G>(settings: Settings, make_gui: F) {
@@ -271,8 +277,12 @@ pub fn run<G: GUI, F: FnOnce(&mut EventCtx) -> G>(settings: Settings, make_gui:
     )
     .unwrap();
 
-    let hidpi_factor = events_loop.get_primary_monitor().get_hidpi_factor();
+    let mut hidpi_factor = events_loop.get_primary_monitor().get_hidpi_factor();
     println!("HiDPI factor is purportedly {}", hidpi_factor);
+    if let Some(x) = settings.override_hidpi_factor {
+        println!("... but overriding it to {} by flag", x);
+        hidpi_factor = x;
+    }
     let mut canvas = Canvas::new(
         settings.initial_dims.0,
         settings.initial_dims.1,

game/src/main.rs

@@ -46,6 +46,9 @@ fn main() {
     if let Some(n) = args.optional_parse("--font_size", |s| s.parse::<usize>()) {
         settings.default_font_size(n);
     }
+    if let Some(x) = args.optional_parse("--hidpi_factor", |x| x.parse::<f64>()) {
+        settings.override_hidpi_factor(x);
+    }
     args.done();
 
     ezgui::run(settings, |ctx| game::Game::new(flags, opts, ctx));