Mainmenu: Avoid the header being displayed behind the formspec (#13924)

This change keeps the current header placement code, but adds additional code to make sure the header doesn't end up behind the formspec.

src/gui/guiEngine.cpp

@@ -283,11 +283,16 @@ void GUIEngine::run()
 		else
 			drawBackground(driver);
 
-		drawHeader(driver);
 		drawFooter(driver);
 
 		m_rendering_engine->get_gui_env()->drawAll();
 
+		// The header *must* be drawn after the menu because it uses
+		// GUIFormspecMenu::getAbsoluteRect().
+		// The header *can* be drawn after the menu because it never intersects
+		// the menu.
+		drawHeader(driver);
+
 		driver->endScene();
 
 		IrrlichtDevice *device = m_rendering_engine->get_raw_device();
@@ -478,29 +483,56 @@ void GUIEngine::drawHeader(video::IVideoDriver *driver)
 
 	video::ITexture* texture = m_textures[TEX_LAYER_HEADER].texture;
 
-	/* If no texture, draw nothing */
-	if(!texture)
+	// If no texture, draw nothing
+	if (!texture)
 		return;
 
+	/*
+	 * Calculate the maximum rectangle
+	 */
+	core::rect<s32> formspec_rect = m_menu->getAbsoluteRect();
+	// 4 px of padding on each side
+	core::rect<s32> max_rect(4, 4, screensize.Width - 8, formspec_rect.UpperLeftCorner.Y - 8);
+
+	// If no space (less than 16x16 px), draw nothing
+	if (max_rect.getWidth() < 16 || max_rect.getHeight() < 16)
+		return;
+
+	/*
+	 * Calculate the preferred rectangle
+	 */
 	f32 mult = (((f32)screensize.Width / 2.0)) /
 			((f32)texture->getOriginalSize().Width);
 
 	v2s32 splashsize(((f32)texture->getOriginalSize().Width) * mult,
 			((f32)texture->getOriginalSize().Height) * mult);
 
-	// Don't draw the header if there isn't enough room
 	s32 free_space = (((s32)screensize.Height)-320)/2;
 
-	if (free_space > splashsize.Y) {
-		core::rect<s32> splashrect(0, 0, splashsize.X, splashsize.Y);
-		splashrect += v2s32((screensize.Width/2)-(splashsize.X/2),
-				((free_space/2)-splashsize.Y/2)+10);
+	core::rect<s32> desired_rect(0, 0, splashsize.X, splashsize.Y);
+	desired_rect += v2s32((screensize.Width/2)-(splashsize.X/2),
+			((free_space/2)-splashsize.Y/2)+10);
+
+	/*
+	 * Make the preferred rectangle fit into the maximum rectangle
+	 */
+	// 1. Scale
+	f32 scale = std::min((f32)max_rect.getWidth() / (f32)desired_rect.getWidth(),
+			(f32)max_rect.getHeight() / (f32)desired_rect.getHeight());
+	if (scale < 1.0f) {
+		v2s32 old_center = desired_rect.getCenter();
+		desired_rect.LowerRightCorner.X = desired_rect.UpperLeftCorner.X + desired_rect.getWidth() * scale;
+		desired_rect.LowerRightCorner.Y = desired_rect.UpperLeftCorner.Y + desired_rect.getHeight() * scale;
+		desired_rect += old_center - desired_rect.getCenter();
+	}
 
-	draw2DImageFilterScaled(driver, texture, splashrect,
+	// 2. Move
+	desired_rect.constrainTo(max_rect);
+
+	draw2DImageFilterScaled(driver, texture, desired_rect,
 		core::rect<s32>(core::position2d<s32>(0,0),
 		core::dimension2di(texture->getOriginalSize())),
 		NULL, NULL, true);
-	}
 }
 
 /******************************************************************************/

src/gui/guiFormSpecMenu.cpp

@@ -247,6 +247,14 @@ std::vector<std::string>* GUIFormSpecMenu::getDropDownValues(const std::string &
 	return NULL;
 }
 
+// This will only return a meaningful value if called after drawMenu().
+core::rect<s32> GUIFormSpecMenu::getAbsoluteRect()
+{
+	core::rect<s32> rect = AbsoluteRect;
+	rect.UpperLeftCorner.Y += m_tabheader_upper_edge;
+	return rect;
+}
+
 v2s32 GUIFormSpecMenu::getElementBasePos(const std::vector<std::string> *v_pos)
 {
 	v2f32 pos_f = v2f32(padding.X, padding.Y) + pos_offset * spacing;
@@ -2104,6 +2112,7 @@ void GUIFormSpecMenu::parseTabHeader(parserData* data, const std::string &elemen
 		e->setActiveTab(tab_index);
 
 	m_fields.push_back(spec);
+	m_tabheader_upper_edge = MYMIN(m_tabheader_upper_edge, rect.UpperLeftCorner.Y);
 }
 
 void GUIFormSpecMenu::parseItemImageButton(parserData* data, const std::string &element)
@@ -3105,6 +3114,7 @@ void GUIFormSpecMenu::regenerateGui(v2u32 screensize)
 
 	m_formspec_version = 1;
 	m_bgcolor = video::SColor(140, 0, 0, 0);
+	m_tabheader_upper_edge = 0;
 
 	{
 		v3f formspec_bgcolor = g_settings->getV3F("formspec_fullscreen_bg_color");

src/gui/guiFormSpecMenu.h

@@ -282,6 +282,9 @@ class GUIFormSpecMenu : public GUIModalMenu
 	GUITable* getTable(const std::string &tablename);
 	std::vector<std::string>* getDropDownValues(const std::string &name);
 
+	// This will only return a meaningful value if called after drawMenu().
+	core::rect<s32> getAbsoluteRect();
+
 #ifdef __ANDROID__
 	bool getAndroidUIInput();
 #endif
@@ -499,6 +502,9 @@ class GUIFormSpecMenu : public GUIModalMenu
 
 	int m_btn_height;
 	gui::IGUIFont *m_font = nullptr;
+
+	// used by getAbsoluteRect
+	s32 m_tabheader_upper_edge = 0;
 };
 
 class FormspecFormSource: public IFormSource