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android: populate dpi_scale from DisplayMetrics.density #647

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Merged
not-fl3 merged 1 commit into from
Jun 15, 2026
+54 −0
Merged

android: populate dpi_scale from DisplayMetrics.density #647

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54 changes: 54 additions & 0 deletions src/native/android.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -190,9 +190,11 @@ impl MainThreadState {
},
Message::SurfaceChanged { width, height } => {
{
let density = unsafe { query_display_density() };
let mut d = crate::native_display().lock().unwrap();
d.screen_width = width as _;
d.screen_height = height as _;
d.dpi_scale = density;
}
self.event_handler.resize_event(width as _, height as _);
}
Expand Down Expand Up @@ -323,6 +325,56 @@ pub unsafe fn attach_jni_env() -> *mut ndk_sys::JNIEnv {
env
}

/// `Resources.getDisplayMetrics().density` — 1.0 = mdpi, 2.0 = xhdpi,
/// etc. Returns 1.0 on any JNI hiccup.
unsafe fn query_display_density() -> f32 {
if VM.is_null() || ACTIVITY.is_null() {
return 1.0;
}
let env = attach_jni_env();
if env.is_null() {
return 1.0;
}

let resources = ndk_utils::call_object_method!(
env,
ACTIVITY,
"getResources",
"()Landroid/content/res/Resources;"
);
if resources.is_null() {
return 1.0;
}

let metrics = ndk_utils::call_object_method!(
env,
resources,
"getDisplayMetrics",
"()Landroid/util/DisplayMetrics;"
);
if metrics.is_null() {
return 1.0;
}

let get_object_class = (**env).GetObjectClass.unwrap();
let get_field_id = (**env).GetFieldID.unwrap();
let get_float_field = (**env).GetFloatField.unwrap();

let metrics_class = get_object_class(env, metrics);
let density_field = get_field_id(
env,
metrics_class,
b"density\0".as_ptr() as _,
b"F\0".as_ptr() as _,
);
if density_field.is_null() {
return 1.0;
}

let density = get_float_field(env, metrics, density_field);
if density > 0.0 { density } else { 1.0 }
}

pub struct AndroidClipboard {}
impl AndroidClipboard {
pub fn new() -> AndroidClipboard {
Expand Down Expand Up @@ -454,9 +506,11 @@ where

let clipboard = Box::new(AndroidClipboard::new());
let tx_fn = Box::new(move |req| tx.send(Message::Request(req)).unwrap());
let density = query_display_density();
crate::set_or_replace_display(NativeDisplayData {
high_dpi: conf.high_dpi,
blocking_event_loop: conf.platform.blocking_event_loop,
dpi_scale: density,
..NativeDisplayData::new(screen_width as _, screen_height as _, tx_fn, clipboard)
});

Expand Down
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