From 4bad4dc8d5cbca8d5ce44413105d110609a6b17a Mon Sep 17 00:00:00 2001
From: Tim Ledbetter <timledbetter@gmail.com>
Date: Thu, 19 Jan 2023 17:52:10 +0000
Subject: [PATCH] PixelPaint: Use background color when cropping layer to
 content

This commit expands the functionality of the "Crop Image to Content"
and "Crop Layer to Content" features by allowing them to detect and
crop the background color of an image instead of just cropping
transparent pixels.

The background color is determined by looking at the corner pixels of
the image. If no background color is found, the old behavior of
cropping transparent pixels is retained.
---
 Userland/Applications/PixelPaint/Layer.cpp | 38 ++++++++++++++++++++--
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/Userland/Applications/PixelPaint/Layer.cpp b/Userland/Applications/PixelPaint/Layer.cpp
index cb318f8f98..e7535bff92 100644
--- a/Userland/Applications/PixelPaint/Layer.cpp
+++ b/Userland/Applications/PixelPaint/Layer.cpp
@@ -335,16 +335,48 @@ void Layer::set_edit_mode(Layer::EditMode mode)
 
 Optional<Gfx::IntRect> Layer::nonempty_content_bounding_rect() const
 {
+    auto determine_background_color = [](NonnullRefPtr<Gfx::Bitmap> const& bitmap) -> Optional<Gfx::Color> {
+        auto bitmap_size = bitmap->size();
+        auto top_left_pixel = bitmap->get_pixel(0, 0);
+        auto top_right_pixel = bitmap->get_pixel(bitmap_size.width() - 1, 0);
+        auto bottom_left_pixel = bitmap->get_pixel(0, bitmap_size.height() - 1);
+        auto bottom_right_pixel = bitmap->get_pixel(bitmap_size.width() - 1, bitmap_size.height() - 1);
+
+        if (top_left_pixel == top_right_pixel || top_left_pixel == bottom_left_pixel)
+            return top_left_pixel;
+
+        if (bottom_right_pixel == bottom_left_pixel || bottom_right_pixel == top_right_pixel)
+            return top_right_pixel;
+
+        return {};
+    };
+
+    enum class ShrinkMode {
+        Alpha,
+        BackgroundColor
+    };
+
     Optional<int> min_content_y;
     Optional<int> min_content_x;
     Optional<int> max_content_y;
     Optional<int> max_content_x;
-
+    auto background_color = determine_background_color(m_content_bitmap);
+    auto shrink_mode = background_color.has_value() ? ShrinkMode::BackgroundColor : ShrinkMode::Alpha;
     for (int y = 0; y < m_content_bitmap->height(); ++y) {
         for (int x = 0; x < m_content_bitmap->width(); ++x) {
             auto color = m_content_bitmap->get_pixel(x, y);
-            if (color.alpha() == 0)
-                continue;
+            switch (shrink_mode) {
+            case ShrinkMode::BackgroundColor:
+                if (color == background_color)
+                    continue;
+                break;
+            case ShrinkMode::Alpha:
+                if (color.alpha() == 0)
+                    continue;
+                break;
+            default:
+                VERIFY_NOT_REACHED();
+            }
             min_content_x = min(min_content_x.value_or(x), x);
             min_content_y = min(min_content_y.value_or(y), y);
             max_content_x = max(max_content_x.value_or(x), x);