From 79f5c49afeff6db89e66c325acf96b36551664a3 Mon Sep 17 00:00:00 2001
From: FrHun <28605587+frhun@users.noreply.github.com>
Date: Tue, 6 Dec 2022 00:12:02 +0100
Subject: [PATCH] Magnifier: Eliminate flickering when downsizing

Previously the content flickered when downsizing the window, because the
previously grabbed frame was still active, but was now too large for the
window.
This crops the source rect to a size where it now perfectly fits the
content area.
---
 .../Applications/Magnifier/MagnifierWidget.cpp   | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/Userland/Applications/Magnifier/MagnifierWidget.cpp b/Userland/Applications/Magnifier/MagnifierWidget.cpp
index ffe0da2505..e5b77ea225 100644
--- a/Userland/Applications/Magnifier/MagnifierWidget.cpp
+++ b/Userland/Applications/Magnifier/MagnifierWidget.cpp
@@ -79,7 +79,7 @@ void MagnifierWidget::sync()
         return;
 
     auto size = frame_inner_rect().size();
-    Gfx::IntSize grab_size { size.width() / m_scale_factor, size.height() / m_scale_factor };
+    Gfx::IntSize grab_size { (size.width() + m_scale_factor - 1) / m_scale_factor, (size.height() + m_scale_factor - 1) / m_scale_factor };
     VERIFY(grab_size.width() != 0 && grab_size.height() != 0);
 
     if (m_locked_location.has_value()) {
@@ -101,8 +101,20 @@ void MagnifierWidget::paint_event(GUI::PaintEvent& event)
 
     GUI::Painter painter(*this);
 
+    if (m_pause_capture)
+        painter.fill_rect(frame_inner_rect(), Gfx::Color::Black);
+
+    // We have to clip the source rect for cases when the currently captured image is larger than the inner_rect
+    int horizontal_clip = (frame_inner_rect().width() + m_scale_factor - 1) / m_scale_factor;
+    int vertical_clip = (frame_inner_rect().height() + m_scale_factor - 1) / m_scale_factor;
+
     if (m_grabbed_bitmap)
-        painter.draw_scaled_bitmap(frame_inner_rect(), *m_grabbed_bitmap, m_grabbed_bitmap->rect(), 1.0, Gfx::Painter::ScalingMode::NearestFractional);
+        painter.draw_scaled_bitmap(
+            frame_inner_rect().intersected(Gfx::IntRect { { 0, 0 }, m_grabbed_bitmap->rect().size() } * m_scale_factor),
+            *m_grabbed_bitmap,
+            m_grabbed_bitmap->rect().intersected({ 0, 0, horizontal_clip, vertical_clip }),
+            1.0,
+            Gfx::Painter::ScalingMode::NearestFractional);
 
     if (m_show_grid) {