From 0b0e95296a8a91aa61de00c0c903804555c884a2 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Wed, 1 Jun 2022 19:12:16 +0100
Subject: [PATCH] Upscale images by integer factors only

Doing anything else results in really poor results, so don't even try
scaling images by 2.25, for example -- scaling by 2 looks much better
and the size difference is relatively insignificant and definitely not
worth the difference in quality.
---
 src/common/bmpbndl.cpp       | 13 +++++++++++--
 tests/graphics/bmpbundle.cpp | 34 +++++++++++++++++++++++++++++-----
 2 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/src/common/bmpbndl.cpp b/src/common/bmpbndl.cpp
index a5300fbb9d..bd00552003 100644
--- a/src/common/bmpbndl.cpp
+++ b/src/common/bmpbndl.cpp
@@ -738,9 +738,18 @@ wxBitmapBundleImpl::DoGetPreferredSize(double scaleTarget,
         const double scaleMax = availableScales[n - 1];
 
         // But check how far is it from the requested scale: if it's more than
-        // 1.5 times smaller, we should still scale it, notably to ensure that
+        // 1.5 times larger, we should still scale it, notably to ensure that
         // bitmaps of standard size are scaled when 2x DPI scaling is used.
-        scaleBest = scaleTarget / scaleMax >= 1.5 ? scaleTarget : scaleMax;
+        if ( scaleTarget >= 1.5*scaleMax )
+        {
+            // However scaling by non-integer scales doesn't work well at all, so
+            // round it to the closest integer in this case.
+            scaleBest = wxRound(scaleTarget);
+        }
+        else // Target scale is not much greater than the biggest one we have.
+        {
+            scaleBest = scaleMax;
+        }
     }
 
     return GetDefaultSize()*scaleBest;
diff --git a/tests/graphics/bmpbundle.cpp b/tests/graphics/bmpbundle.cpp
index a703fe0bec..17367b02b4 100644
--- a/tests/graphics/bmpbundle.cpp
+++ b/tests/graphics/bmpbundle.cpp
@@ -51,13 +51,36 @@ TEST_CASE("BitmapBundle::FromBitmaps", "[bmpbundle]")
 
 TEST_CASE("BitmapBundle::GetPreferredSize", "[bmpbundle]")
 {
-    CHECK( wxBitmapBundle().GetPreferredBitmapSizeAtScale(1) == wxDefaultSize );
+    // Check that empty bundle doesn't have any preferred size.
+    wxBitmapBundle b;
+    CHECK( b.GetPreferredBitmapSizeAtScale(1) == wxDefaultSize );
 
     const wxSize normal(32, 32);
     const wxSize bigger(64, 64);
+    const wxSize triple(96, 96);
 
-    const wxBitmapBundle
-        b = wxBitmapBundle::FromBitmaps(wxBitmap(normal), wxBitmap(bigger));
+
+    // Then check what happens if there is only a single bitmap.
+    b = wxBitmapBundle::FromBitmap(wxBitmap(normal));
+
+    // We should avoid scaling as long as the size is close enough to the
+    // actual bitmap size.
+    CHECK( b.GetPreferredBitmapSizeAtScale(0   ) == normal );
+    CHECK( b.GetPreferredBitmapSizeAtScale(1   ) == normal );
+    CHECK( b.GetPreferredBitmapSizeAtScale(1.25) == normal );
+    CHECK( b.GetPreferredBitmapSizeAtScale(1.4 ) == normal );
+
+    // Once it becomes too big, we're going to need to scale, but we should be
+    // scaling by an integer factor.
+    CHECK( b.GetPreferredBitmapSizeAtScale(1.5 ) == bigger );
+    CHECK( b.GetPreferredBitmapSizeAtScale(1.75) == bigger );
+    CHECK( b.GetPreferredBitmapSizeAtScale(2   ) == bigger );
+    CHECK( b.GetPreferredBitmapSizeAtScale(2.25) == bigger );
+    CHECK( b.GetPreferredBitmapSizeAtScale(2.5 ) == triple );
+
+
+    // Now check what happens when there is also a double size bitmap.
+    b = wxBitmapBundle::FromBitmaps(wxBitmap(normal), wxBitmap(bigger));
 
     // Check that the existing bitmaps are used without scaling for most of the
     // typical scaling values.
@@ -71,8 +94,9 @@ TEST_CASE("BitmapBundle::GetPreferredSize", "[bmpbundle]")
     CHECK( b.GetPreferredBitmapSizeAtScale(2.5 ) == bigger );
 
     // This scale is too big to use any of the existing bitmaps, so they will
-    // be scaled.
-    CHECK( b.GetPreferredBitmapSizeAtScale(3   ) == 3*normal );
+    // be scaled, but use integer factors.
+    CHECK( b.GetPreferredBitmapSizeAtScale(3   ) == triple );
+    CHECK( b.GetPreferredBitmapSizeAtScale(3.33) == triple );
 }
 
 #ifdef wxHAS_DPI_INDEPENDENT_PIXELS