From ae7271b7259437f613f7bca0a3b71ee7ebfa9c51 Mon Sep 17 00:00:00 2001
From: DS <ds.desour@proton.me>
Date: Fri, 14 Apr 2023 21:05:09 +0200
Subject: [PATCH] Fix background[] pos-offset lower-right-corner being at least
 (1,1) (#13320)

IGUIElement has a MinSize for the RelativeRect, which is at least (1,1).
This means a pos offset of (0,0) will cause a seemingly off-by-1 error at the
lower right corner, and (0.1,0.1) for example will just not work on the lower
right corner.
Ergo, we can't use the AbsoluteRect for storing the pos offset.
---
 src/gui/guiBackgroundImage.cpp | 16 +++++++++++-----
 src/gui/guiBackgroundImage.h   |  4 +++-
 src/gui/guiFormSpecMenu.cpp    |  9 +++++----
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/gui/guiBackgroundImage.cpp b/src/gui/guiBackgroundImage.cpp
index 8d0d1c010..987287fce 100644
--- a/src/gui/guiBackgroundImage.cpp
+++ b/src/gui/guiBackgroundImage.cpp
@@ -22,9 +22,10 @@ OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 GUIBackgroundImage::GUIBackgroundImage(gui::IGUIEnvironment *env,
 	gui::IGUIElement *parent, s32 id, const core::rect<s32> &rectangle,
 	const std::string &name, const core::rect<s32> &middle,
-	ISimpleTextureSource *tsrc, bool autoclip) :
+	ISimpleTextureSource *tsrc, bool autoclip, v2s32 autoclip_offset) :
 	gui::IGUIElement(gui::EGUIET_ELEMENT, env, parent, id, rectangle),
-	m_name(name), m_middle(middle), m_tsrc(tsrc), m_autoclip(autoclip)
+	m_name(name), m_middle(middle), m_tsrc(tsrc), m_autoclip(autoclip),
+	m_autoclip_offset(autoclip_offset)
 {
 }
 
@@ -42,9 +43,14 @@ void GUIBackgroundImage::draw()
 		return;
 	}
 
-	core::rect<s32> rect = AbsoluteRect;
-	if (m_autoclip)
-		rect.LowerRightCorner += Parent->getAbsoluteClippingRect().getSize();
+	core::rect<s32> rect;
+	if (m_autoclip) {
+		rect = Parent->getAbsoluteClippingRect();
+		rect.UpperLeftCorner -= m_autoclip_offset;
+		rect.LowerRightCorner += m_autoclip_offset;
+	} else {
+		rect = AbsoluteRect;
+	}
 
 	video::IVideoDriver *driver = Environment->getVideoDriver();
 
diff --git a/src/gui/guiBackgroundImage.h b/src/gui/guiBackgroundImage.h
index 31fbfd09c..2e51a8190 100644
--- a/src/gui/guiBackgroundImage.h
+++ b/src/gui/guiBackgroundImage.h
@@ -26,7 +26,8 @@ class GUIBackgroundImage : public gui::IGUIElement
 public:
 	GUIBackgroundImage(gui::IGUIEnvironment *env, gui::IGUIElement *parent, s32 id,
 		const core::rect<s32> &rectangle, const std::string &name,
-		const core::rect<s32> &middle, ISimpleTextureSource *tsrc, bool autoclip);
+		const core::rect<s32> &middle, ISimpleTextureSource *tsrc, bool autoclip,
+		v2s32 autoclip_offset);
 
 	virtual void draw() override;
 
@@ -35,4 +36,5 @@ private:
 	core::rect<s32> m_middle;
 	ISimpleTextureSource *m_tsrc;
 	bool m_autoclip;
+	v2s32 m_autoclip_offset;
 };
diff --git a/src/gui/guiFormSpecMenu.cpp b/src/gui/guiFormSpecMenu.cpp
index 16183211d..e48f13d25 100644
--- a/src/gui/guiFormSpecMenu.cpp
+++ b/src/gui/guiFormSpecMenu.cpp
@@ -1101,17 +1101,18 @@ void GUIFormSpecMenu::parseBackground(parserData* data, const std::string &eleme
 		258 + m_fields.size()
 	);
 
-	core::rect<s32> rect;
+	core::rect<s32> rect{};
+	v2s32 autoclip_offset{};
 	if (!clip) {
 		// no auto_clip => position like normal image
 		rect = core::rect<s32>(pos, pos + geom);
 	} else {
-		// it will be auto-clipped when drawing
-		rect = core::rect<s32>(-pos, pos);
+		// element will be auto-clipped when drawing
+		autoclip_offset = pos;
 	}
 
 	GUIBackgroundImage *e = new GUIBackgroundImage(Environment, data->background_parent.get(),
-			spec.fid, rect, name, middle, m_tsrc, clip);
+			spec.fid, rect, name, middle, m_tsrc, clip, autoclip_offset);
 
 	FATAL_ERROR_IF(!e, "Failed to create background formspec element");