[librsvg/librsvg-2.50] (#730): Incorrect text spacing when the transform is not 1:1

[Federico Mena Quintero <federico src gnome org>]

commit afba7f2fcae0505113450198f74c8bf95c3cc13c
Author: Federico Mena Quintero <federico gnome org>
Date:   Mon May 24 18:34:49 2021 -0500

    (#730): Incorrect text spacing when the transform is not 1:1
    
    Three things here:
    
    * The main one, context.set_round_glyph_positions(false) on the Pango
    context.  This is what was causing incorrect text spacing when the
    transform does not have 1:1 scaling.
    
    * Set HintStyle::None and HintMetrics::Off.  These seem to cause
    inconsistencies when the transform is not an identity matrix.
    
    * Set the font options on the cr, not on the Pango context, as the
    latter will pick up the options from the cr anyway.
    
    Fixes https://gitlab.gnome.org/GNOME/librsvg/-/issues/730

 rsvg_internals/src/drawing_ctx.rs                  |  36 +++++++++++++++------
 .../reftests/bugs/730-font-scaling-ref.png         | Bin 0 -> 14781 bytes
 tests/fixtures/reftests/bugs/730-font-scaling.svg  |  18 +++++++++++
 3 files changed, 44 insertions(+), 10 deletions(-)
---
diff --git a/rsvg_internals/src/drawing_ctx.rs b/rsvg_internals/src/drawing_ctx.rs
index f7da9675..e176e691 100644
--- a/rsvg_internals/src/drawing_ctx.rs
+++ b/rsvg_internals/src/drawing_ctx.rs
@@ -1,8 +1,11 @@
 //! The main context structure which drives the drawing process.
 
 use float_cmp::approx_eq;
+use glib::translate::*;
+use glib_sys::gboolean;
 use once_cell::sync::Lazy;
 use pango::FontMapExt;
+use pango_sys::PangoContext;
 use regex::{Captures, Regex};
 use std::borrow::Cow;
 use std::cell::RefCell;
@@ -2054,8 +2057,31 @@ impl From<TextRendering> for cairo::Antialias {
 impl From<&DrawingCtx> for pango::Context {
     fn from(draw_ctx: &DrawingCtx) -> pango::Context {
         let cr = draw_ctx.cr.clone();
+
+        let mut options = cairo::FontOptions::new();
+        if draw_ctx.testing {
+            options.set_antialias(cairo::Antialias::Gray);
+        }
+
+        options.set_hint_style(cairo::HintStyle::None);
+        options.set_hint_metrics(cairo::HintMetrics::Off);
+
+        cr.set_font_options(&options);
+
         let font_map = pangocairo::FontMap::get_default().unwrap();
         let context = font_map.create_context().unwrap();
+
+        unsafe {
+            extern "C" {
+                fn pango_context_set_round_glyph_positions(
+                    context: *mut PangoContext,
+                    round_positions: gboolean,
+                );
+            }
+
+            pango_context_set_round_glyph_positions(context.to_glib_none().0, false.to_glib());
+        }
+
         pangocairo::functions::update_context(&cr, &context);
 
         // Pango says this about pango_cairo_context_set_resolution():
@@ -2076,16 +2102,6 @@ impl From<&DrawingCtx> for pango::Context {
         // code.
         pangocairo::functions::context_set_resolution(&context, 72.0);
 
-        if draw_ctx.testing {
-            let mut options = cairo::FontOptions::new();
-
-            options.set_antialias(cairo::Antialias::Gray);
-            options.set_hint_style(cairo::HintStyle::Full);
-            options.set_hint_metrics(cairo::HintMetrics::On);
-
-            pangocairo::functions::context_set_font_options(&context, Some(&options));
-        }
-
         context
     }
 }
diff --git a/tests/fixtures/reftests/bugs/730-font-scaling-ref.png 
b/tests/fixtures/reftests/bugs/730-font-scaling-ref.png
new file mode 100644
index 00000000..a4a152fd
Binary files /dev/null and b/tests/fixtures/reftests/bugs/730-font-scaling-ref.png differ
diff --git a/tests/fixtures/reftests/bugs/730-font-scaling.svg 
b/tests/fixtures/reftests/bugs/730-font-scaling.svg
new file mode 100644
index 00000000..5a8ea2b8
--- /dev/null
+++ b/tests/fixtures/reftests/bugs/730-font-scaling.svg
@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg"; width="500" height="200">
+  <svg x="10" y="0" width="480" height="40" viewBox="0 0 480 40">
+    <text x="0" y="25" font-size="20" font-family="sans">How vexingly quick daft zebras jump!</text>
+  </svg>
+
+  <svg x="10" y="40" width="480" height="40" viewBox="0 0 240 20">
+    <text x="0" y="12.5" font-size="10" font-family="sans">How vexingly quick daft zebras jump!</text>
+  </svg>
+
+  <svg x="10" y="80" width="480" height="40" viewBox="0 0 120 10">
+    <text x="0" y="6.25" font-size="5" font-family="sans">How vexingly quick daft zebras jump!</text>
+  </svg>
+
+  <svg x="10" y="120" width="480" height="40" viewBox="0 0 60 5">
+    <text x="0" y="3.125" font-size="2.5" font-family="sans">How vexingly quick daft zebras jump!</text>
+  </svg>
+</svg>