egui_plot: use f64 for translate (#4637)

<!--
Please read the "Making a PR" section of
[`CONTRIBUTING.md`](https://github.com/emilk/egui/blob/master/CONTRIBUTING.md)
before opening a Pull Request!

* Keep your PR:s small and focused.
* The PR title is what ends up in the changelog, so make it descriptive!
* If applicable, add a screenshot or gif.
* If it is a non-trivial addition, consider adding a demo for it to
`egui_demo_lib`, or a new example.
* Do NOT open PR:s from your `master` branch, as that makes it hard for
maintainers to add commits to your PR.
* Remember to run `cargo fmt` and `cargo clippy`.
* Open the PR as a draft until you have self-reviewed it and run
`./scripts/check.sh`.
* When you have addressed a PR comment, mark it as resolved.

Please be patient! I will review your PR, but my time is limited!
-->

Can fix translating with high zoom out
#3462



* Maybe related to #3656

crates/egui_plot/src/lib.rs

@@ -961,6 +961,7 @@ impl<'a> Plot<'a> {
                     mem.auto_bounds = false.into();
                 }
                 BoundsModification::Translate(delta) => {
+                    let delta = (delta.x as f64, delta.y as f64);
                     bounds.translate(delta);
                     mem.auto_bounds = false.into();
                 }
@@ -1034,7 +1035,8 @@ impl<'a> Plot<'a> {
             if !allow_drag.y {
                 delta.y = 0.0;
             }
-            mem.transform.translate_bounds(delta);
+            mem.transform
+                .translate_bounds((delta.x as f64, delta.y as f64));
             mem.auto_bounds = mem.auto_bounds.and(!allow_drag);
         }
 
@@ -1123,7 +1125,8 @@ impl<'a> Plot<'a> {
                     scroll_delta.y = 0.0;
                 }
                 if scroll_delta != Vec2::ZERO {
-                    mem.transform.translate_bounds(-scroll_delta);
+                    mem.transform
+                        .translate_bounds((-scroll_delta.x as f64, -scroll_delta.y as f64));
                     mem.auto_bounds = false.into();
                 }
             }

crates/egui_plot/src/transform.rs

@@ -184,9 +184,9 @@ impl PlotBounds {
     }
 
     #[inline]
-    pub fn translate(&mut self, delta: Vec2) {
-        self.translate_x(delta.x as f64);
-        self.translate_y(delta.y as f64);
+    pub fn translate(&mut self, delta: (f64, f64)) {
+        self.translate_x(delta.0);
+        self.translate_y(delta.1);
     }
 
     #[inline]
@@ -321,16 +321,16 @@ impl PlotTransform {
         self.bounds = bounds;
     }
 
-    pub fn translate_bounds(&mut self, mut delta_pos: Vec2) {
+    pub fn translate_bounds(&mut self, mut delta_pos: (f64, f64)) {
         if self.x_centered {
-            delta_pos.x = 0.;
+            delta_pos.0 = 0.;
         }
         if self.y_centered {
-            delta_pos.y = 0.;
+            delta_pos.1 = 0.;
         }
-        delta_pos.x *= self.dvalue_dpos()[0] as f32;
-        delta_pos.y *= self.dvalue_dpos()[1] as f32;
-        self.bounds.translate(delta_pos);
+        delta_pos.0 *= self.dvalue_dpos()[0];
+        delta_pos.1 *= self.dvalue_dpos()[1];
+        self.bounds.translate((delta_pos.0, delta_pos.1));
     }
 
     /// Zoom by a relative factor with the given screen position as center.