Add tessellation option to toggle rounding text to pixel coordinates

On by default and only there for testing

egui/src/introspection.rs

@@ -136,6 +136,7 @@ impl Widget for &mut epaint::TessellationOptions {
                 aa_size: _,
                 anti_alias,
                 coarse_tessellation_culling,
+                round_text_to_pixels,
                 debug_paint_clip_rects,
                 debug_paint_text_rects,
                 debug_ignore_clip_rects,
@@ -147,6 +148,9 @@ impl Widget for &mut epaint::TessellationOptions {
                     coarse_tessellation_culling,
                     "Do coarse culling in the tessellator",
                 );
+                ui.checkbox(round_text_to_pixels, "Align text positions to pixel grid")
+                    .on_hover_text("Most text already is, so don't expect to see a large change.");
+
                 ui.checkbox(debug_ignore_clip_rects, "Ignore clip rectangles");
                 ui.checkbox(debug_paint_clip_rects, "Paint clip rectangles");
                 ui.checkbox(debug_paint_text_rects, "Paint text bounds");

epaint/src/tessellator.rs

@@ -274,6 +274,10 @@ pub struct TessellationOptions {
     /// This likely makes
     pub coarse_tessellation_culling: bool,
 
+    /// If `true` (default) align text to mesh grid.
+    /// This makes the text sharper on most platforms.
+    pub round_text_to_pixels: bool,
+
     /// Output the clip rectangles to be painted.
     pub debug_paint_clip_rects: bool,
 
@@ -291,6 +295,7 @@ impl Default for TessellationOptions {
             aa_size: 1.0,
             anti_alias: true,
             coarse_tessellation_culling: true,
+            round_text_to_pixels: true,
             debug_paint_text_rects: false,
             debug_paint_clip_rects: false,
             debug_ignore_clip_rects: false,
@@ -311,7 +316,11 @@ impl TessellationOptions {
 impl TessellationOptions {
     #[inline(always)]
     pub fn round_to_pixel(&self, point: f32) -> f32 {
-        (point * self.pixels_per_point).round() / self.pixels_per_point
+        if self.round_text_to_pixels {
+            (point * self.pixels_per_point).round() / self.pixels_per_point
+        } else {
+            point
+        }
     }
 }