LibGfx: Make it possible to apply an (integer) scale to a Painter

This adds a scale factor to Painter, which will be used for HighDPI
support. It's also a step towards general affine transforms on Painters.

All of Painter's public API takes logical coordinates, while some
internals deal with physical coordinates now. If scale == 1, logical
and physical coordinates are the same. For scale == 2, a 200x100 bitmap
would be covered by a logical {0, 0, 100, 50} rect, while its physical
size would be {0, 0, 200, 100}.

Most of Painter's functions just assert that scale() == 1 is for now,
but most functions called by WindowServer are updated to handle
arbitrary (integer) scale.

Also add a new Demo "LibGfxScaleDemo" that covers the converted
functions and that can be used to iteratively add scaling support
to more functions.

To make Painter's interface deal with logical coordinates only,
make translation() and clip_rect() non-public.

7 files changed, 288 insertions, 73 deletions

diff --git a/Base/res/apps/LibGfxScaleDemo.af b/Base/res/apps/LibGfxScaleDemo.af
new file mode 100644
index 0000000000..0548f43885
--- /dev/null
+++ b/Base/res/apps/LibGfxScaleDemo.af
@@ -0,0 +1,4 @@
+[App]
+Name=LibGfx Scale Demo
+Executable=/bin/LibGfxScaleDemo
+Category=Demos
diff --git a/Documentation/HighDPI.md b/Documentation/HighDPI.md
index 96b1eb1a5a..0043e77a6a 100644
--- a/Documentation/HighDPI.md
+++ b/Documentation/HighDPI.md
@@ -34,4 +34,4 @@ The plan is to have all applications use highdpi backbuffers eventually. It'll t
 3. Let apps opt in to high-res window framebuffers, and convert all apps one-by-one
 4. Remove high-res window framebuffer opt-in since all apps have it now.
 
-We're currently before point 0.
+We're currently before point 1.
diff --git a/Userland/Demos/CMakeLists.txt b/Userland/Demos/CMakeLists.txt
index ace09e2ea9..5d1e01b90f 100644
--- a/Userland/Demos/CMakeLists.txt
+++ b/Userland/Demos/CMakeLists.txt
@@ -3,6 +3,7 @@ add_subdirectory(Cube)
 add_subdirectory(Eyes)
 add_subdirectory(Fire)
 add_subdirectory(LibGfxDemo)
+add_subdirectory(LibGfxScaleDemo)
 add_subdirectory(Mouse)
 add_subdirectory(Screensaver)
 add_subdirectory(WidgetGallery)
diff --git a/Userland/Demos/LibGfxScaleDemo/CMakeLists.txt b/Userland/Demos/LibGfxScaleDemo/CMakeLists.txt
new file mode 100644
index 0000000000..38f441dab9
--- /dev/null
+++ b/Userland/Demos/LibGfxScaleDemo/CMakeLists.txt
@@ -0,0 +1,6 @@
+set(SOURCES
+    main.cpp
+)
+
+serenity_app(LibGfxScaleDemo ICON app-libgfx-demo)
+target_link_libraries(LibGfxScaleDemo LibGUI LibIPC LibGfx LibCore)
diff --git a/Userland/Demos/LibGfxScaleDemo/main.cpp b/Userland/Demos/LibGfxScaleDemo/main.cpp
new file mode 100644
index 0000000000..ade1e1da62
--- /dev/null
+++ b/Userland/Demos/LibGfxScaleDemo/main.cpp
@@ -0,0 +1,121 @@
+/*
+ * Copyright (c) 2020, Nico Weber <thakis@chromium.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <LibGUI/Application.h>
+#include <LibGUI/Icon.h>
+#include <LibGUI/Painter.h>
+#include <LibGUI/Widget.h>
+#include <LibGUI/Window.h>
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/FontDatabase.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/Palette.h>
+#include <LibGfx/Path.h>
+#include <LibGfx/WindowTheme.h>
+
+const int WIDTH = 300;
+const int HEIGHT = 200;
+
+class Canvas final : public GUI::Widget {
+    C_OBJECT(Canvas)
+public:
+    virtual ~Canvas() override;
+
+private:
+    Canvas();
+    RefPtr<Gfx::Bitmap> m_bitmap_1x;
+    RefPtr<Gfx::Bitmap> m_bitmap_2x;
+
+    void draw(Gfx::Painter& painter);
+    virtual void paint_event(GUI::PaintEvent&) override;
+};
+
+Canvas::Canvas()
+{
+    m_bitmap_1x = Gfx::Bitmap::create(Gfx::BitmapFormat::RGB32, { WIDTH, HEIGHT });
+    m_bitmap_2x = Gfx::Bitmap::create(Gfx::BitmapFormat::RGB32, { WIDTH * 2, HEIGHT * 2 });
+
+    Gfx::Painter painter_1x(*m_bitmap_1x);
+    draw(painter_1x);
+
+    Gfx::Painter painter_2x(*m_bitmap_2x);
+    painter_2x.scale(2);
+    draw(painter_2x);
+
+    update();
+}
+
+Canvas::~Canvas()
+{
+}
+
+void Canvas::paint_event(GUI::PaintEvent& event)
+{
+    GUI::Painter painter(*this);
+    painter.add_clip_rect(event.rect());
+    painter.fill_rect(event.rect(), Color::Magenta);
+    painter.blit({ 0, 0 }, *m_bitmap_1x, m_bitmap_1x->rect());
+    painter.blit({ 0, HEIGHT }, *m_bitmap_2x, m_bitmap_2x->rect());
+}
+
+void Canvas::draw(Gfx::Painter& painter)
+{
+    auto active_window_icon = Gfx::Bitmap::load_from_file("/res/icons/16x16/window.png");
+    Gfx::WindowTheme::current().paint_normal_frame(painter, Gfx::WindowTheme::WindowState::Active, { 4, 18, WIDTH - 8, HEIGHT - 29 }, "Well hello friends", *active_window_icon, palette(), { WIDTH - 20, 6, 16, 16 });
+}
+
+int main(int argc, char** argv)
+{
+    auto app = GUI::Application::construct(argc, argv);
+
+    if (pledge("stdio rpath shared_buffer", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    if (unveil("/res", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil(nullptr, nullptr) < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    auto window = GUI::Window::construct();
+    window->set_title("LibGfx Scale Demo");
+    window->set_resizable(false);
+    window->resize(WIDTH * 2, HEIGHT * 3);
+
+    auto app_icon = GUI::Icon::default_icon("app-libgfx-demo");
+    window->set_icon(app_icon.bitmap_for_size(16));
+    window->set_main_widget<Canvas>();
+    window->show();
+
+    return app->exec();
+}
diff --git a/Userland/Libraries/LibGfx/Painter.cpp b/Userland/Libraries/LibGfx/Painter.cpp
index ab2c06d171..4244a3b42d 100644
--- a/Userland/Libraries/LibGfx/Painter.cpp
+++ b/Userland/Libraries/LibGfx/Painter.cpp
@@ -84,6 +84,8 @@ Painter::~Painter()
 
 void Painter::fill_rect_with_draw_op(const IntRect& a_rect, Color color)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto rect = a_rect.translated(translation()).intersected(clip_rect());
     if (rect.is_empty())
         return;
@@ -100,7 +102,7 @@ void Painter::fill_rect_with_draw_op(const IntRect& a_rect, Color color)
 
 void Painter::clear_rect(const IntRect& a_rect, Color color)
 {
-    auto rect = a_rect.translated(translation()).intersected(clip_rect());
+    auto rect = to_physical(a_rect).intersected(clip_rect());
     if (rect.is_empty())
         return;
 
@@ -115,6 +117,23 @@ void Painter::clear_rect(const IntRect& a_rect, Color color)
     }
 }
 
+void Painter::fill_physical_rect(const IntRect& a_rect, Color color)
+{
+    auto rect = a_rect.intersected(clip_rect());
+    if (rect.is_empty())
+        return;
+    ASSERT(m_target->rect().contains(rect));
+
+    RGBA32* dst = m_target->scanline(rect.top()) + rect.left();
+    const size_t dst_skip = m_target->pitch() / sizeof(RGBA32);
+
+    for (int i = rect.height() - 1; i >= 0; --i) {
+        for (int j = 0; j < rect.width(); ++j)
+            dst[j] = Color::from_rgba(dst[j]).blend(color).value();
+        dst += dst_skip;
+    }
+}
+
 void Painter::fill_rect(const IntRect& a_rect, Color color)
 {
     if (color.alpha() == 0)
@@ -130,24 +149,13 @@ void Painter::fill_rect(const IntRect& a_rect, Color color)
         return;
     }
 
-    auto rect = a_rect.translated(translation()).intersected(clip_rect());
-    if (rect.is_empty())
-        return;
-
-    ASSERT(m_target->rect().contains(rect));
-
-    RGBA32* dst = m_target->scanline(rect.top()) + rect.left();
-    const size_t dst_skip = m_target->pitch() / sizeof(RGBA32);
-
-    for (int i = rect.height() - 1; i >= 0; --i) {
-        for (int j = 0; j < rect.width(); ++j)
-            dst[j] = Color::from_rgba(dst[j]).blend(color).value();
-        dst += dst_skip;
-    }
+    fill_physical_rect(to_physical(a_rect), color);
 }
 
 void Painter::fill_rect_with_dither_pattern(const IntRect& a_rect, Color color_a, Color color_b)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto rect = a_rect.translated(translation()).intersected(clip_rect());
     if (rect.is_empty())
         return;
@@ -170,6 +178,8 @@ void Painter::fill_rect_with_dither_pattern(const IntRect& a_rect, Color color_a
 
 void Painter::fill_rect_with_checkerboard(const IntRect& a_rect, const IntSize& cell_size, Color color_dark, Color color_light)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto rect = a_rect.translated(translation()).intersected(clip_rect());
     if (rect.is_empty())
         return;
@@ -189,10 +199,12 @@ void Painter::fill_rect_with_checkerboard(const IntRect& a_rect, const IntSize&
 
 void Painter::fill_rect_with_gradient(Orientation orientation, const IntRect& a_rect, Color gradient_start, Color gradient_end)
 {
+
 #ifdef NO_FPU
     return fill_rect(a_rect, gradient_start);
 #endif
-    auto rect = a_rect.translated(translation());
+
+    auto rect = to_physical(a_rect);
     auto clipped_rect = IntRect::intersection(rect, clip_rect());
     if (clipped_rect.is_empty())
         return;
@@ -233,6 +245,8 @@ void Painter::fill_rect_with_gradient(const IntRect& a_rect, Color gradient_star
 
 void Painter::fill_ellipse(const IntRect& a_rect, Color color)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto rect = a_rect.translated(translation()).intersected(clip_rect());
     if (rect.is_empty())
         return;
@@ -252,6 +266,8 @@ void Painter::fill_ellipse(const IntRect& a_rect, Color color)
 
 void Painter::draw_ellipse_intersecting(const IntRect& rect, Color color, int thickness)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     constexpr int number_samples = 100; // FIXME: dynamically work out the number of samples based upon the rect size
     double increment = M_PI / number_samples;
 
@@ -289,6 +305,8 @@ static void for_each_pixel_around_rect_clockwise(const RectType& rect, Callback
 
 void Painter::draw_focus_rect(const IntRect& rect, Color color)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     if (rect.is_empty())
         return;
     bool state = false;
@@ -301,6 +319,8 @@ void Painter::draw_focus_rect(const IntRect& rect, Color color)
 
 void Painter::draw_rect(const IntRect& a_rect, Color color, bool rough)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     IntRect rect = a_rect.translated(translation());
     auto clipped_rect = rect.intersected(clip_rect());
     if (clipped_rect.is_empty())
@@ -345,6 +365,8 @@ void Painter::draw_rect(const IntRect& a_rect, Color color, bool rough)
 
 void Painter::draw_bitmap(const IntPoint& p, const CharacterBitmap& bitmap, Color color)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto rect = IntRect(p, bitmap.size()).translated(translation());
     auto clipped_rect = rect.intersected(clip_rect());
     if (clipped_rect.is_empty())
@@ -371,7 +393,7 @@ void Painter::draw_bitmap(const IntPoint& p, const CharacterBitmap& bitmap, Colo
 
 void Painter::draw_bitmap(const IntPoint& p, const GlyphBitmap& bitmap, Color color)
 {
-    auto dst_rect = IntRect(p, bitmap.size()).translated(translation());
+    auto dst_rect = to_physical(IntRect(p, bitmap.size()));
     auto clipped_rect = dst_rect.intersected(clip_rect());
     if (clipped_rect.is_empty())
         return;
@@ -382,17 +404,29 @@ void Painter::draw_bitmap(const IntPoint& p, const GlyphBitmap& bitmap, Color co
     RGBA32* dst = m_target->scanline(clipped_rect.y()) + clipped_rect.x();
     const size_t dst_skip = m_target->pitch() / sizeof(RGBA32);
 
-    for (int row = first_row; row <= last_row; ++row) {
-        for (int j = 0; j <= (last_column - first_column); ++j) {
-            if (bitmap.bit_at(j + first_column, row))
-                dst[j] = color.value();
+    if (scale() == 1) {
+        for (int row = first_row; row <= last_row; ++row) {
+            for (int j = 0; j <= (last_column - first_column); ++j) {
+                if (bitmap.bit_at(j + first_column, row))
+                    dst[j] = color.value();
+            }
+            dst += dst_skip;
+        }
+    } else {
+        for (int row = first_row; row <= last_row; ++row) {
+            for (int j = 0; j <= (last_column - first_column); ++j) {
+                if (bitmap.bit_at((j + first_column) / scale(), row / scale()))
+                    dst[j] = color.value();
+            }
+            dst += dst_skip;
         }
-        dst += dst_skip;
     }
 }
 
 void Painter::draw_triangle(const IntPoint& a, const IntPoint& b, const IntPoint& c, Color color)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     RGBA32 rgba = color.value();
 
     IntPoint p0(a);
@@ -426,7 +460,7 @@ void Painter::draw_triangle(const IntPoint& a, const IntPoint& b, const IntPoint
         top = clip.top();
     }
 
-    for (int y = top; y < p1.y() && y < clip.bottom(); ++y) {
+    for (int y = top; y < p1.y() && y < clip.bottom(); ++y) { // XXX <=?
         int start = x01 > x02 ? max((int)x02, clip.left()) : max((int)x01, clip.left());
         int end = x01 > x02 ? min((int)x01, clip.right()) : min((int)x02, clip.right());
         auto* scanline = m_target->scanline(y);
@@ -447,7 +481,7 @@ void Painter::draw_triangle(const IntPoint& a, const IntPoint& b, const IntPoint
         top = clip.top();
     }
 
-    for (int y = top; y < p2.y() && y < clip.bottom(); ++y) {
+    for (int y = top; y < p2.y() && y < clip.bottom(); ++y) { // XXX <=?
         int start = x12 > x02 ? max((int)x02, clip.left()) : max((int)x12, clip.left());
         int end = x12 > x02 ? min((int)x12, clip.right()) : min((int)x02, clip.right());
         auto* scanline = m_target->scanline(y);
@@ -461,6 +495,8 @@ void Painter::draw_triangle(const IntPoint& a, const IntPoint& b, const IntPoint
 
 void Painter::blit_scaled(const IntRect& dst_rect_raw, const Gfx::Bitmap& source, const IntRect& src_rect, float hscale, float vscale)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto dst_rect = IntRect(dst_rect_raw.location(), dst_rect_raw.size()).translated(translation());
     auto clipped_rect = dst_rect.intersected(clip_rect());
     if (clipped_rect.is_empty())
@@ -491,6 +527,8 @@ void Painter::blit_scaled(const IntRect& dst_rect_raw, const Gfx::Bitmap& source
 
 void Painter::blit_with_opacity(const IntPoint& position, const Gfx::Bitmap& source, const IntRect& src_rect, float opacity)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     ASSERT(!m_target->has_alpha_channel());
 
     if (!opacity)
@@ -529,6 +567,8 @@ void Painter::blit_with_opacity(const IntPoint& position, const Gfx::Bitmap& sou
 
 void Painter::blit_filtered(const IntPoint& position, const Gfx::Bitmap& source, const IntRect& src_rect, Function<Color(Color)> filter)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     IntRect safe_src_rect = src_rect.intersected(source.rect());
     auto dst_rect = IntRect(position, safe_src_rect.size()).translated(translation());
     auto clipped_rect = dst_rect.intersected(clip_rect());
@@ -574,6 +614,8 @@ void Painter::blit_dimmed(const IntPoint& position, const Gfx::Bitmap& source, c
 
 void Painter::draw_tiled_bitmap(const IntRect& a_dst_rect, const Gfx::Bitmap& source)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto dst_rect = a_dst_rect.translated(translation());
     auto clipped_rect = dst_rect.intersected(clip_rect());
     if (clipped_rect.is_empty())
@@ -600,11 +642,10 @@ void Painter::draw_tiled_bitmap(const IntRect& a_dst_rect, const Gfx::Bitmap& so
     ASSERT_NOT_REACHED();
 }
 
-void Painter::blit_offset(const IntPoint& position,
-    const Gfx::Bitmap& source,
-    const IntRect& src_rect,
-    const IntPoint& offset)
+void Painter::blit_offset(const IntPoint& position, const Gfx::Bitmap& source, const IntRect& src_rect, const IntPoint& offset)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto dst_rect = IntRect(position, src_rect.size()).translated(translation());
     auto clipped_rect = dst_rect.intersected(clip_rect());
     if (clipped_rect.is_empty())
@@ -639,6 +680,9 @@ void Painter::blit_offset(const IntPoint& position,
 
 void Painter::blit_with_alpha(const IntPoint& position, const Gfx::Bitmap& source, const IntRect& src_rect)
 {
+    if (scale() != 1)
+        return draw_scaled_bitmap({ position, src_rect.size() }, source, src_rect);
+
     ASSERT(source.has_alpha_channel());
     IntRect safe_src_rect = src_rect.intersected(source.rect());
     auto dst_rect = IntRect(position, safe_src_rect.size()).translated(translation());
@@ -675,6 +719,9 @@ void Painter::blit(const IntPoint& position, const Gfx::Bitmap& source, const In
         return blit_with_opacity(position, source, src_rect, opacity);
     if (source.has_alpha_channel())
         return blit_with_alpha(position, source, src_rect);
+    if (scale() != 1)
+        return draw_scaled_bitmap({ position, src_rect.size() }, source, src_rect, opacity);
+
     auto safe_src_rect = src_rect.intersected(source.rect());
     ASSERT(source.rect().contains(safe_src_rect));
     auto dst_rect = IntRect(position, safe_src_rect.size()).translated(translation());
@@ -714,13 +761,13 @@ void Painter::blit(const IntPoint& position, const Gfx::Bitmap& source, const In
 }
 
 template<bool has_alpha_channel, typename GetPixel>
-ALWAYS_INLINE static void do_draw_integer_scaled_bitmap(Gfx::Bitmap& target, const IntRect& dst_rect, const Gfx::Bitmap& source, int hfactor, int vfactor, GetPixel get_pixel, float opacity)
+ALWAYS_INLINE static void do_draw_integer_scaled_bitmap(Gfx::Bitmap& target, const IntRect& dst_rect, const IntRect& src_rect, const Gfx::Bitmap& source, int hfactor, int vfactor, GetPixel get_pixel, float opacity)
 {
     bool has_opacity = opacity != 1.0f;
-    for (int y = source.rect().top(); y <= source.rect().bottom(); ++y) {
+    for (int y = 0; y < src_rect.height(); ++y) {
         int dst_y = dst_rect.y() + y * vfactor;
-        for (int x = source.rect().left(); x <= source.rect().right(); ++x) {
-            auto src_pixel = get_pixel(source, x, y);
+        for (int x = 0; x < src_rect.width(); ++x) {
+            auto src_pixel = get_pixel(source, x + src_rect.left(), y + src_rect.top());
             if (has_opacity)
                 src_pixel.set_alpha(src_pixel.alpha() * opacity);
             for (int yo = 0; yo < vfactor; ++yo) {
@@ -744,12 +791,12 @@ ALWAYS_INLINE static void do_draw_scaled_bitmap(Gfx::Bitmap& target, const IntRe
         int hfactor = dst_rect.width() / src_rect.width();
         int vfactor = dst_rect.height() / src_rect.height();
         if (hfactor == 2 && vfactor == 2)
-            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, source, 2, 2, get_pixel, opacity);
+            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, src_rect, source, 2, 2, get_pixel, opacity);
         if (hfactor == 3 && vfactor == 3)
-            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, source, 3, 3, get_pixel, opacity);
+            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, src_rect, source, 3, 3, get_pixel, opacity);
         if (hfactor == 4 && vfactor == 4)
-            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, source, 4, 4, get_pixel, opacity);
-        return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, source, hfactor, vfactor, get_pixel, opacity);
+            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, src_rect, source, 4, 4, get_pixel, opacity);
+        return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, src_rect, source, hfactor, vfactor, get_pixel, opacity);
     }
 
     bool has_opacity = opacity != 1.0f;
@@ -772,13 +819,14 @@ ALWAYS_INLINE static void do_draw_scaled_bitmap(Gfx::Bitmap& target, const IntRe
 
 void Painter::draw_scaled_bitmap(const IntRect& a_dst_rect, const Gfx::Bitmap& source, const IntRect& src_rect, float opacity)
 {
-    auto dst_rect = a_dst_rect;
-    if (dst_rect.size() == src_rect.size())
-        return blit(dst_rect.location(), source, src_rect, opacity);
+    if (scale() == 1 && a_dst_rect.size() == src_rect.size())
+        return blit(a_dst_rect.location(), source, src_rect, opacity);
+
+    auto dst_rect = to_physical(a_dst_rect);
 
     auto safe_src_rect = src_rect.intersected(source.rect());
     ASSERT(source.rect().contains(safe_src_rect));
-    dst_rect.move_by(state().translation);
+
     auto clipped_rect = dst_rect.intersected(clip_rect());
     if (clipped_rect.is_empty())
         return;
@@ -1084,6 +1132,8 @@ void Painter::draw_text(const IntRect& rect, const Utf32View& text, const Font&
 
 void Painter::draw_text(Function<void(const IntRect&, u32)> draw_one_glyph, const IntRect& rect, const StringView& raw_text, const Font& font, TextAlignment alignment, TextElision elision)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     Utf8View text { raw_text };
     do_draw_text(rect, text, font, alignment, elision, [&](const IntRect& r, u32 code_point) {
         draw_one_glyph(r, code_point);
@@ -1092,6 +1142,8 @@ void Painter::draw_text(Function<void(const IntRect&, u32)> draw_one_glyph, cons
 
 void Painter::draw_text(Function<void(const IntRect&, u32)> draw_one_glyph, const IntRect& rect, const Utf8View& text, const Font& font, TextAlignment alignment, TextElision elision)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     do_draw_text(rect, text, font, alignment, elision, [&](const IntRect& r, u32 code_point) {
         draw_one_glyph(r, code_point);
     });
@@ -1099,6 +1151,8 @@ void Painter::draw_text(Function<void(const IntRect&, u32)> draw_one_glyph, cons
 
 void Painter::draw_text(Function<void(const IntRect&, u32)> draw_one_glyph, const IntRect& rect, const Utf32View& text, const Font& font, TextAlignment alignment, TextElision elision)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     do_draw_text(rect, text, font, alignment, elision, [&](const IntRect& r, u32 code_point) {
         draw_one_glyph(r, code_point);
     });
@@ -1106,6 +1160,8 @@ void Painter::draw_text(Function<void(const IntRect&, u32)> draw_one_glyph, cons
 
 void Painter::set_pixel(const IntPoint& p, Color color)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto point = p;
     point.move_by(state().translation);
     if (!clip_rect().contains(point))
@@ -1115,6 +1171,8 @@ void Painter::set_pixel(const IntPoint& p, Color color)
 
 ALWAYS_INLINE void Painter::set_pixel_with_draw_op(u32& pixel, const Color& color)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     switch (draw_op()) {
     case DrawOp::Copy:
         pixel = color.value();
@@ -1130,6 +1188,8 @@ ALWAYS_INLINE void Painter::set_pixel_with_draw_op(u32& pixel, const Color& colo
 
 ALWAYS_INLINE void Painter::fill_scanline_with_draw_op(int y, int x, int width, const Color& color)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     switch (draw_op()) {
     case DrawOp::Copy:
         fast_u32_fill(m_target->scanline(y) + x, color.value(), width);
@@ -1155,14 +1215,20 @@ ALWAYS_INLINE void Painter::fill_scanline_with_draw_op(int y, int x, int width,
     }
 }
 
-void Painter::draw_pixel(const IntPoint& position, Color color, int thickness)
+void Painter::draw_physical_pixel(const IntPoint& position, Color color, int thickness)
 {
-    if (thickness == 1) {
+    // This always draws a single physical pixel, independent of scale().
+    // This should only be called by routines that already handle scale
+    // (including scaling thickness).
+    ASSERT(draw_op() == DrawOp::Copy);
+
+    if (thickness == 1) { // Implies scale() == 1.
         auto& pixel = m_target->scanline(position.y())[position.x()];
         return set_pixel_with_draw_op(pixel, Color::from_rgba(pixel).blend(color));
     }
-    IntRect rect { position.translated(-(thickness / 2), -(thickness / 2)), { thickness, thickness } };
-    fill_rect(rect.translated(-state().translation), color);
+
+    IntRect rect { position, { thickness, thickness } };
+    fill_physical_rect(rect, color);
 }
 
 void Painter::draw_line(const IntPoint& p1, const IntPoint& p2, Color color, int thickness, LineStyle style)
@@ -1172,11 +1238,9 @@ void Painter::draw_line(const IntPoint& p1, const IntPoint& p2, Color color, int
 
     auto clip_rect = this->clip_rect();
 
-    auto point1 = p1;
-    point1.move_by(state().translation);
-
-    auto point2 = p2;
-    point2.move_by(state().translation);
+    auto point1 = to_physical(p1);
+    auto point2 = to_physical(p2);
+    thickness *= scale();
 
     // Special case: vertical line.
     if (point1.x() == point2.x()) {
@@ -1193,16 +1257,16 @@ void Painter::draw_line(const IntPoint& p1, const IntPoint& p2, Color color, int
         int max_y = min(point2.y(), clip_rect.bottom());
         if (style == LineStyle::Dotted) {
             for (int y = min_y; y <= max_y; y += thickness * 2)
-                draw_pixel({ x, y }, color, thickness);
+                draw_physical_pixel({ x, y }, color, thickness);
         } else if (style == LineStyle::Dashed) {
             for (int y = min_y; y <= max_y; y += thickness * 6) {
-                draw_pixel({ x, y }, color, thickness);
-                draw_pixel({ x, min(y + thickness, max_y) }, color, thickness);
-                draw_pixel({ x, min(y + thickness * 2, max_y) }, color, thickness);
+                draw_physical_pixel({ x, y }, color, thickness);
+                draw_physical_pixel({ x, min(y + thickness, max_y) }, color, thickness);
+                draw_physical_pixel({ x, min(y + thickness * 2, max_y) }, color, thickness);
             }
         } else {
-            for (int y = min_y; y <= max_y; ++y)
-                draw_pixel({ x, y }, color, thickness);
+            for (int y = min_y; y <= max_y; y += thickness)
+                draw_physical_pixel({ x, y }, color, thickness);
         }
         return;
     }
@@ -1222,16 +1286,16 @@ void Painter::draw_line(const IntPoint& p1, const IntPoint& p2, Color color, int
         int max_x = min(point2.x(), clip_rect.right());
         if (style == LineStyle::Dotted) {
             for (int x = min_x; x <= max_x; x += thickness * 2)
-                draw_pixel({ x, y }, color, thickness);
+                draw_physical_pixel({ x, y }, color, thickness);
         } else if (style == LineStyle::Dashed) {
             for (int x = min_x; x <= max_x; x += thickness * 6) {
-                draw_pixel({ x, y }, color, thickness);
-                draw_pixel({ min(x + thickness, max_x), y }, color, thickness);
-                draw_pixel({ min(x + thickness * 2, max_x), y }, color, thickness);
+                draw_physical_pixel({ x, y }, color, thickness);
+                draw_physical_pixel({ min(x + thickness, max_x), y }, color, thickness);
+                draw_physical_pixel({ min(x + thickness * 2, max_x), y }, color, thickness);
             }
         } else {
-            for (int x = min_x; x <= max_x; ++x)
-                draw_pixel({ x, y }, color, thickness);
+            for (int x = min_x; x <= max_x; x += thickness)
+                draw_physical_pixel({ x, y }, color, thickness);
         }
         return;
     }
@@ -1261,7 +1325,7 @@ void Painter::draw_line(const IntPoint& p1, const IntPoint& p2, Color color, int
         int y = point1.y();
         for (int x = point1.x(); x <= point2.x(); ++x) {
             if (clip_rect.contains(x, y))
-                draw_pixel({ x, y }, color, thickness);
+                draw_physical_pixel({ x, y }, color, thickness);
             error += delta_error;
             if (error >= 0.5) {
                 y = (double)y + y_step;
@@ -1274,7 +1338,7 @@ void Painter::draw_line(const IntPoint& p1, const IntPoint& p2, Color color, int
         int x = point1.x();
         for (int y = point1.y(); y <= point2.y(); ++y) {
             if (clip_rect.contains(x, y))
-                draw_pixel({ x, y }, color, thickness);
+                draw_physical_pixel({ x, y }, color, thickness);
             error += delta_error;
             if (error >= 0.5) {
                 x = (double)x + x_step;
@@ -1316,6 +1380,7 @@ static bool can_approximate_bezier_curve(const FloatPoint& p1, const FloatPoint&
     return max(p1x, p2x) + max(p1y, p2y) <= tolerance;
 }
 
+// static
 void Painter::for_each_line_segment_on_bezier_curve(const FloatPoint& control_point, const FloatPoint& p1, const FloatPoint& p2, Function<void(const FloatPoint&, const FloatPoint&)>& callback)
 {
     if (can_approximate_bezier_curve(p1, p2, control_point)) {
@@ -1371,11 +1436,14 @@ static bool can_approximate_elliptical_arc(const FloatPoint& p1, const FloatPoin
 
 void Painter::draw_quadratic_bezier_curve(const IntPoint& control_point, const IntPoint& p1, const IntPoint& p2, Color color, int thickness, LineStyle style)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     for_each_line_segment_on_bezier_curve(FloatPoint(control_point), FloatPoint(p1), FloatPoint(p2), [&](const FloatPoint& fp1, const FloatPoint& fp2) {
         draw_line(IntPoint(fp1.x(), fp1.y()), IntPoint(fp2.x(), fp2.y()), color, thickness, style);
     });
 }
 
+// static
 void Painter::for_each_line_segment_on_elliptical_arc(const FloatPoint& p1, const FloatPoint& p2, const FloatPoint& center, const FloatPoint radii, float x_axis_rotation, float theta_1, float theta_delta, Function<void(const FloatPoint&, const FloatPoint&)>& callback)
 {
     if (can_approximate_elliptical_arc(p1, p2, center, radii, x_axis_rotation, theta_1, theta_delta)) {
@@ -1385,6 +1453,7 @@ void Painter::for_each_line_segment_on_elliptical_arc(const FloatPoint& p1, cons
     }
 }
 
+// static
 void Painter::for_each_line_segment_on_elliptical_arc(const FloatPoint& p1, const FloatPoint& p2, const FloatPoint& center, const FloatPoint radii, float x_axis_rotation, float theta_1, float theta_delta, Function<void(const FloatPoint&, const FloatPoint&)>&& callback)
 {
     for_each_line_segment_on_elliptical_arc(p1, p2, center, radii, x_axis_rotation, theta_1, theta_delta, callback);
@@ -1392,6 +1461,8 @@ void Painter::for_each_line_segment_on_elliptical_arc(const FloatPoint& p1, cons
 
 void Painter::draw_elliptical_arc(const IntPoint& p1, const IntPoint& p2, const IntPoint& center, const FloatPoint& radii, float x_axis_rotation, float theta_1, float theta_delta, Color color, int thickness, LineStyle style)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     for_each_line_segment_on_elliptical_arc(FloatPoint(p1), FloatPoint(p2), FloatPoint(center), radii, x_axis_rotation, theta_1, theta_delta, [&](const FloatPoint& fp1, const FloatPoint& fp2) {
         draw_line(IntPoint(fp1.x(), fp1.y()), IntPoint(fp2.x(), fp2.y()), color, thickness, style);
     });
@@ -1399,8 +1470,8 @@ void Painter::draw_elliptical_arc(const IntPoint& p1, const IntPoint& p2, const
 
 void Painter::add_clip_rect(const IntRect& rect)
 {
-    state().clip_rect.intersect(rect.translated(translation()));
-    state().clip_rect.intersect(m_target->rect());
+    state().clip_rect.intersect(to_physical(rect));
+    state().clip_rect.intersect(m_target->rect()); // FIXME: This shouldn't be necessary?
 }
 
 void Painter::clear_clip_rect()
@@ -1421,6 +1492,8 @@ PainterStateSaver::~PainterStateSaver()
 
 void Painter::stroke_path(const Path& path, Color color, int thickness)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     FloatPoint cursor;
 
     for (auto& segment : path.segments()) {
@@ -1476,6 +1549,8 @@ void Painter::stroke_path(const Path& path, Color color, int thickness)
 
 void Painter::fill_path(Path& path, Color color, WindingRule winding_rule)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     const auto& segments = path.split_lines();
 
     if (segments.size() == 0)
@@ -1615,6 +1690,8 @@ void Painter::fill_path(Path& path, Color color, WindingRule winding_rule)
 
 void Painter::blit_disabled(const IntPoint& location, const Gfx::Bitmap& bitmap, const IntRect& rect, const Palette& palette)
 {
+    ASSERT(scale() == 1); // FIXME: Add scaling support.
+
     auto bright_color = palette.threed_highlight();
     auto dark_color = palette.threed_shadow1();
     blit_filtered(location.translated(1, 1), bitmap, rect, [&](auto) {
diff --git a/Userland/Libraries/LibGfx/Painter.h b/Userland/Libraries/LibGfx/Painter.h
index 8ae33fc207..d8bb2f7cb2 100644
--- a/Userland/Libraries/LibGfx/Painter.h
+++ b/Userland/Libraries/LibGfx/Painter.h
@@ -116,12 +116,10 @@ public:
 
     void add_clip_rect(const IntRect& rect);
     void clear_clip_rect();
-    IntRect clip_rect() const { return state().clip_rect; }
-
-    void translate(int dx, int dy) { state().translation.move_by(dx, dy); }
-    void translate(const IntPoint& delta) { state().translation.move_by(delta); }
 
-    IntPoint translation() const { return state().translation; }
+    void translate(int dx, int dy) { translate({ dx, dy }); }
+    void translate(const IntPoint& delta) { state().translation.move_by(delta * state().scale); }
+    void scale(int s) { state().scale *= s; }
 
     Gfx::Bitmap* target() { return m_target.ptr(); }
 
@@ -133,23 +131,31 @@ public:
     }
 
 protected:
+    IntPoint translation() const { return state().translation; }
+    IntRect to_physical(const IntRect& r) const { return (r * scale()).translated(translation()); }
+    IntPoint to_physical(const IntPoint& p) const { return (p * scale()).translated(translation()); }
+    int scale() const { return state().scale; }
     void set_pixel_with_draw_op(u32& pixel, const Color&);
     void fill_scanline_with_draw_op(int y, int x, int width, const Color& color);
     void fill_rect_with_draw_op(const IntRect&, Color);
     void blit_with_alpha(const IntPoint&, const Gfx::Bitmap&, const IntRect& src_rect);
     void blit_with_opacity(const IntPoint&, const Gfx::Bitmap&, const IntRect& src_rect, float opacity);
-    void draw_pixel(const IntPoint&, Color, int thickness = 1);
+    void draw_physical_pixel(const IntPoint&, Color, int thickness = 1);
+    IntRect clip_rect() const { return state().clip_rect; }
 
     struct State {
         const Font* font;
         IntPoint translation;
-        IntRect clip_rect;
+        int scale = 1;
+        IntRect clip_rect; // In physical coordinates.
         DrawOp draw_op;
     };
 
     State& state() { return m_state_stack.last(); }
     const State& state() const { return m_state_stack.last(); }
 
+    void fill_physical_rect(const IntRect&, Color);
+
     IntRect m_clip_origin;
     NonnullRefPtr<Gfx::Bitmap> m_target;
     Vector<State, 4> m_state_stack;