Scale form elements consistently

The ratios between the sizes of form elements, including text, is now
fixed, aside from variations caused by rounding.  This makes form layout
almost fully predictable, and particularly independent of player's
screen size.  The proportions of non-text elements are the traditional
proportions.

For compatibility, the way in which element positions and sizes are
specified remains unchanged, in all its baroqueness, with one exception.
The exception is that the position of a label[] element is now defined
in terms of the vertically center of the first line of the label,
rather than the bottom of the first line of the label.  This change
allows a label to be precisely aligned with button text or an edit box,
which are positioned in a centering manner.  Label positioning remains
consistent with the previous system, just more precisely defined.

Make multi-line label[] elements work properly.  Previously the code set
a bounding rectangle assuming that there would be only a single line,
and as a result a multi-line label would be cut somewhere in the middle
of the second line.  Now multi-line labels not only work, but have
guaranteed line spacing relative to inventory slots, to aid alignment.

Incidentally fix tabheader[] elements which were being constrained to
the wrong width.

Given an unusually large form, in variable-size mode, the form rendering
system now chooses a scale that will fit the entire form on the screen,
if that doesn't make elements too small.  Fixed-size forms, including the
main menu, are have their sizes fixed in inch terms.  The fixed size for
fixed-size forms and the preferred and minimum sizes for variable-size
forms all scale according to the gui_scaling parameter.

3 files changed, 287 insertions, 209 deletions

diff --git a/src/constants.h b/src/constants.h
index d23f6bdf4..8e39ccb74 100644
--- a/src/constants.h
+++ b/src/constants.h
@@ -100,9 +100,6 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #define LEGACY_SCALING                                     (2./3.)
 #define TTF_DEFAULT_FONT_SIZE              (13.0 / LEGACY_SCALING)
 #define DEFAULT_FONT_SIZE                                     (14)
-#define DEFAULT_IMGSIZE                                     (48.0)
-#define DEFAULT_XSPACING                    ((15.0 + (1.0 / 3.0)))
-#define DEFAULT_YSPACING                                     (9.0)
 
 #endif
 
diff --git a/src/guiFormSpecMenu.cpp b/src/guiFormSpecMenu.cpp
index cca27b777..c81238a65 100644
--- a/src/guiFormSpecMenu.cpp
+++ b/src/guiFormSpecMenu.cpp
@@ -51,6 +51,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "settings.h"
 #include "client.h"
 #include "util/string.h" // for parseColorString()
+#include "fontengine.h"
 
 #define MY_CHECKPOS(a,b)													\
 	if (v_pos.size() != 2) {												\
@@ -68,6 +69,44 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 /*
 	GUIFormSpecMenu
 */
+static unsigned int font_line_height(gui::IGUIFont *font)
+{
+	return font->getDimension(L"Ay").Height + font->getKerningHeight();
+}
+
+static gui::IGUIFont *select_font_by_line_height(double target_line_height)
+{
+	// We don't get to directly select a font according to its
+	// baseline-to-baseline height.  Rather, we select by em size.
+	// The ratio between these varies between fonts.  The font
+	// engine also takes its size parameter not specified in pixels,
+	// as we want, but scaled by display density and gui_scaling,
+	// so invert that scaling here.  Use a binary search among
+	// requested sizes to find the right font.  Our starting bounds
+	// are an em height of 1 (being careful not to request size 0,
+	// which crashes the freetype system) and an em height of the
+	// target baseline-to-baseline height.
+	unsigned int loreq = ceil(1 / porting::getDisplayDensity()
+				/ g_settings->getFloat("gui_scaling"));
+	unsigned int hireq = ceil(target_line_height
+				/ porting::getDisplayDensity()
+				/ g_settings->getFloat("gui_scaling"));
+	unsigned int lohgt = font_line_height(glb_fontengine->getFont(loreq));
+	unsigned int hihgt = font_line_height(glb_fontengine->getFont(hireq));
+	while(hireq - loreq > 1 && lohgt != hihgt) {
+		unsigned int nureq = (loreq + hireq) >> 1;
+		unsigned int nuhgt = font_line_height(glb_fontengine->getFont(nureq));
+		if(nuhgt < target_line_height) {
+			loreq = nureq;
+			lohgt = nuhgt;
+		} else {
+			hireq = nureq;
+			hihgt = nuhgt;
+		}
+	}
+	return glb_fontengine->getFont(target_line_height - lohgt < hihgt - target_line_height ? loreq : hireq);
+}
+
 GUIFormSpecMenu::GUIFormSpecMenu(irr::IrrlichtDevice* dev,
 		gui::IGUIElement* parent, s32 id, IMenuManager *menumgr,
 		InventoryManager *invmgr, IGameDef *gamedef,
@@ -89,7 +128,8 @@ GUIFormSpecMenu::GUIFormSpecMenu(irr::IrrlichtDevice* dev,
 	m_lock(false),
 	m_form_src(fsrc),
 	m_text_dst(tdst),
-	m_formspec_version(0)
+	m_formspec_version(0),
+	m_font(NULL)
 #ifdef __ANDROID__
 	,m_JavaDialogFieldName(L"")
 #endif
@@ -266,13 +306,11 @@ void GUIFormSpecMenu::parseSize(parserData* data,std::string element)
 	if (((parts.size() == 2) || parts.size() == 3) ||
 		((parts.size() > 3) && (m_formspec_version > FORMSPEC_API_VERSION)))
 	{
-		v2f invsize;
-
 		if (parts[1].find(';') != std::string::npos)
 			parts[1] = parts[1].substr(0,parts[1].find(';'));
 
-		invsize.X = stof(parts[0]);
-		invsize.Y = stof(parts[1]);
+		data->invsize.X = MYMAX(0, stof(parts[0]));
+		data->invsize.Y = MYMAX(0, stof(parts[1]));
 
 		lockSize(false);
 		if (parts.size() == 3) {
@@ -281,70 +319,7 @@ void GUIFormSpecMenu::parseSize(parserData* data,std::string element)
 			}
 		}
 
-		double cur_scaling = porting::getDisplayDensity() *
-				g_settings->getFloat("gui_scaling");
-
-		if (m_lock) {
-			v2u32 current_screensize = m_device->getVideoDriver()->getScreenSize();
-			v2u32 delta = current_screensize - m_lockscreensize;
-
-			if (current_screensize.Y > m_lockscreensize.Y)
-				delta.Y /= 2;
-			else
-				delta.Y = 0;
-
-			if (current_screensize.X > m_lockscreensize.X)
-				delta.X /= 2;
-			else
-				delta.X = 0;
-
-			offset = v2s32(delta.X,delta.Y);
-
-			data->screensize = m_lockscreensize;
-
-			// fixed scaling for fixed size gui elements */
-			cur_scaling = LEGACY_SCALING;
-		}
-		else {
-			offset = v2s32(0,0);
-		}
-
-		/* adjust image size to dpi */
-		int y_partition = 15;
-		imgsize = v2s32(data->screensize.Y/y_partition, data->screensize.Y/y_partition);
-		int min_imgsize = DEFAULT_IMGSIZE * cur_scaling;
-		while ((min_imgsize > imgsize.Y) && (y_partition > 1)) {
-			y_partition--;
-			imgsize = v2s32(data->screensize.Y/y_partition, data->screensize.Y/y_partition);
-		}
-		assert(y_partition > 0);
-
-		/* adjust spacing to dpi */
-		spacing = v2s32(imgsize.X+(DEFAULT_XSPACING * cur_scaling),
-				imgsize.Y+(DEFAULT_YSPACING * cur_scaling));
-
-		padding = v2s32(data->screensize.Y/imgsize.Y, data->screensize.Y/imgsize.Y);
-
-		/* adjust padding to dpi */
-		padding = v2s32(
-				(padding.X/(2.0/3.0)) * cur_scaling,
-				(padding.X/(2.0/3.0)) * cur_scaling
-				);
-		data->size = v2s32(
-			padding.X*2+spacing.X*(invsize.X-1.0)+imgsize.X,
-			padding.Y*2+spacing.Y*(invsize.Y-1.0)+imgsize.Y + m_btn_height - 5
-		);
-		data->rect = core::rect<s32>(
-				data->screensize.X/2 - data->size.X/2 + offset.X,
-				data->screensize.Y/2 - data->size.Y/2 + offset.Y,
-				data->screensize.X/2 + data->size.X/2 + offset.X,
-				data->screensize.Y/2 + data->size.Y/2 + offset.Y
-		);
-
-		DesiredRect = data->rect;
-		recalculateAbsolutePosition(false);
-		data->basepos = getBasePos();
-		data->bp_set = 2;
+		data->explicit_size = true;
 		return;
 	}
 	errorstream<< "Invalid size element (" << parts.size() << "): '" << element << "'"  << std::endl;
@@ -397,7 +372,7 @@ void GUIFormSpecMenu::parseList(parserData* data,std::string element)
 			return;
 		}
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of list without a size[] element"<<std::endl;
 		m_inventorylists.push_back(ListDrawSpec(loc, listname, pos, geom, start_i));
 		return;
@@ -433,14 +408,9 @@ void GUIFormSpecMenu::parseCheckbox(parserData* data,std::string element)
 
 		std::wstring wlabel = narrow_to_wide(label.c_str());
 
-		gui::IGUIFont *font = NULL;
-		gui::IGUISkin* skin = Environment->getSkin();
-		if (skin)
-			font = skin->getFont();
-
 		core::rect<s32> rect = core::rect<s32>(
 				pos.X, pos.Y + ((imgsize.Y/2) - m_btn_height),
-				pos.X + font->getDimension(wlabel.c_str()).Width + 25, // text size + size of checkbox
+				pos.X + m_font->getDimension(wlabel.c_str()).Width + 25, // text size + size of checkbox
 				pos.Y + ((imgsize.Y/2) + m_btn_height));
 
 		FieldSpec spec(
@@ -518,35 +488,6 @@ void GUIFormSpecMenu::parseScrollBar(parserData* data, std::string element)
 		e->setSmallStep(10);
 		e->setLargeStep(100);
 
-		if (!m_lock) {
-			core::rect<s32> relative_rect = e->getRelativePosition();
-
-			if (!is_horizontal) {
-				s32 original_width = relative_rect.getWidth();
-				s32 width = (original_width/(2.0/3.0))
-						* porting::getDisplayDensity()
-						* g_settings->getFloat("gui_scaling");
-				e->setRelativePosition(core::rect<s32>(
-						relative_rect.UpperLeftCorner.X,
-						relative_rect.UpperLeftCorner.Y,
-						relative_rect.LowerRightCorner.X + (width - original_width),
-						relative_rect.LowerRightCorner.Y
-					));
-			}
-			else  {
-				s32 original_height = relative_rect.getHeight();
-				s32 height = (original_height/(2.0/3.0))
-						* porting::getDisplayDensity()
-						* g_settings->getFloat("gui_scaling");
-				e->setRelativePosition(core::rect<s32>(
-						relative_rect.UpperLeftCorner.X,
-						relative_rect.UpperLeftCorner.Y,
-						relative_rect.LowerRightCorner.X,
-						relative_rect.LowerRightCorner.Y + (height - original_height)
-					));
-			}
-		}
-
 		m_scrollbars.push_back(std::pair<FieldSpec,gui::IGUIScrollBar*>(spec,e));
 		m_fields.push_back(spec);
 		return;
@@ -576,7 +517,7 @@ void GUIFormSpecMenu::parseImage(parserData* data,std::string element)
 		geom.X = stof(v_geom[0]) * (float)imgsize.X;
 		geom.Y = stof(v_geom[1]) * (float)imgsize.Y;
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of image without a size[] element"<<std::endl;
 		m_images.push_back(ImageDrawSpec(name, pos, geom));
 		return;
@@ -592,7 +533,7 @@ void GUIFormSpecMenu::parseImage(parserData* data,std::string element)
 		pos.X += stof(v_pos[0]) * (float) spacing.X;
 		pos.Y += stof(v_pos[1]) * (float) spacing.Y;
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of image without a size[] element"<<std::endl;
 		m_images.push_back(ImageDrawSpec(name, pos));
 		return;
@@ -622,7 +563,7 @@ void GUIFormSpecMenu::parseItemImage(parserData* data,std::string element)
 		geom.X = stof(v_geom[0]) * (float)imgsize.X;
 		geom.Y = stof(v_geom[1]) * (float)imgsize.Y;
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of item_image without a size[] element"<<std::endl;
 		m_itemimages.push_back(ImageDrawSpec(name, pos, geom));
 		return;
@@ -658,7 +599,7 @@ void GUIFormSpecMenu::parseButton(parserData* data,std::string element,
 				core::rect<s32>(pos.X, pos.Y - m_btn_height,
 						pos.X + geom.X, pos.Y + m_btn_height);
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of button without a size[] element"<<std::endl;
 
 		label = unescape_string(label);
@@ -717,7 +658,7 @@ void GUIFormSpecMenu::parseBackground(parserData* data,std::string element)
 			}
 		}
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of background without a size[] element"<<std::endl;
 		m_backgrounds.push_back(ImageDrawSpec(name, pos, geom));
 		return;
@@ -1008,8 +949,9 @@ void GUIFormSpecMenu::parsePwdField(parserData* data,std::string element)
 
 		if (label.length() >= 1)
 		{
-			rect.UpperLeftCorner.Y -= m_btn_height;
-			rect.LowerRightCorner.Y = rect.UpperLeftCorner.Y + m_btn_height;
+			int font_height = font_line_height(m_font);
+			rect.UpperLeftCorner.Y -= font_height;
+			rect.LowerRightCorner.Y = rect.UpperLeftCorner.Y + font_height;
 			Environment->addStaticText(spec.flabel.c_str(), rect, false, true, this, 0);
 		}
 
@@ -1038,20 +980,7 @@ void GUIFormSpecMenu::parseSimpleField(parserData* data,
 
 	core::rect<s32> rect;
 
-	if(!data->bp_set)
-	{
-		rect = core::rect<s32>(
-			data->screensize.X/2 - 580/2,
-			data->screensize.Y/2 - 300/2,
-			data->screensize.X/2 + 580/2,
-			data->screensize.Y/2 + 300/2
-		);
-		DesiredRect = rect;
-		recalculateAbsolutePosition(false);
-		data->basepos = getBasePos();
-		data->bp_set = 1;
-	}
-	else if(data->bp_set == 2)
+	if(data->explicit_size)
 		errorstream<<"WARNING: invalid use of unpositioned \"field\" in inventory"<<std::endl;
 
 	v2s32 pos = padding + AbsoluteRect.UpperLeftCorner;
@@ -1103,8 +1032,9 @@ void GUIFormSpecMenu::parseSimpleField(parserData* data,
 
 		if (label.length() >= 1)
 		{
-			rect.UpperLeftCorner.Y -= m_btn_height;
-			rect.LowerRightCorner.Y = rect.UpperLeftCorner.Y + m_btn_height;
+			int font_height = font_line_height(m_font);
+			rect.UpperLeftCorner.Y -= font_height;
+			rect.LowerRightCorner.Y = rect.UpperLeftCorner.Y + font_height;
 			Environment->addStaticText(spec.flabel.c_str(), rect, false, true, this, 0);
 		}
 	}
@@ -1147,7 +1077,7 @@ void GUIFormSpecMenu::parseTextArea(parserData* data,
 
 	core::rect<s32> rect = core::rect<s32>(pos.X, pos.Y, pos.X+geom.X, pos.Y+geom.Y);
 
-	if(data->bp_set != 2)
+	if(!data->explicit_size)
 		errorstream<<"WARNING: invalid use of positioned "<<type<<" without a size[] element"<<std::endl;
 
 	if(m_form_src)
@@ -1199,8 +1129,9 @@ void GUIFormSpecMenu::parseTextArea(parserData* data,
 
 		if (label.length() >= 1)
 		{
-			rect.UpperLeftCorner.Y -= m_btn_height;
-			rect.LowerRightCorner.Y = rect.UpperLeftCorner.Y + m_btn_height;
+			int font_height = font_line_height(m_font);
+			rect.UpperLeftCorner.Y -= font_height;
+			rect.LowerRightCorner.Y = rect.UpperLeftCorner.Y + font_height;
 			Environment->addStaticText(spec.flabel.c_str(), rect, false, true, this, 0);
 		}
 	}
@@ -1240,33 +1171,46 @@ void GUIFormSpecMenu::parseLabel(parserData* data,std::string element)
 
 		v2s32 pos = padding;
 		pos.X += stof(v_pos[0]) * (float)spacing.X;
-		pos.Y += stof(v_pos[1]) * (float)spacing.Y;
+		pos.Y += (stof(v_pos[1]) + 7.0/30.0) * (float)spacing.Y;
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of label without a size[] element"<<std::endl;
 
-		text = unescape_string(text);
-
-		std::wstring wlabel = narrow_to_wide(text.c_str());
-
-		gui::IGUIFont *font = NULL;
-				gui::IGUISkin* skin = Environment->getSkin();
-				if (skin)
-					font = skin->getFont();
+		int font_height = font_line_height(m_font);
 
-		core::rect<s32> rect = core::rect<s32>(
-				pos.X, pos.Y+((imgsize.Y/2) - m_btn_height),
-				pos.X + font->getDimension(wlabel.c_str()).Width,
-				pos.Y+((imgsize.Y/2) + m_btn_height));
+		text = unescape_string(text);
+		std::vector<std::string> lines = split(text, '\n');
+
+		for (unsigned int i = 0; i != lines.size(); i++) {
+			// Lines are spaced at the nominal distance of
+			// 2/5 inventory slot, even if the font doesn't
+			// quite match that.  This provides consistent
+			// form layout, at the expense of sometimes
+			// having sub-optimal spacing for the font.
+			// We multiply by 2 and then divide by 5, rather
+			// than multiply by 0.4, to get exact results
+			// in the integer cases: 0.4 is not exactly
+			// representable in binary floating point.
+			s32 posy = pos.Y + ((float)i) * spacing.Y * 2.0 / 5.0;
+			std::wstring wlabel = narrow_to_wide(lines[i].c_str());
+			core::rect<s32> rect = core::rect<s32>(
+				pos.X, posy - font_height,
+				pos.X + m_font->getDimension(wlabel.c_str()).Width,
+				posy + font_height);
+			FieldSpec spec(
+				L"",
+				wlabel,
+				L"",
+				258+m_fields.size()
+			);
+			gui::IGUIStaticText *e =
+				Environment->addStaticText(spec.flabel.c_str(),
+					rect, false, false, this, spec.fid);
+			e->setTextAlignment(gui::EGUIA_UPPERLEFT,
+						gui::EGUIA_CENTER);
+			m_fields.push_back(spec);
+		}
 
-		FieldSpec spec(
-			L"",
-			wlabel,
-			L"",
-			258+m_fields.size()
-		);
-		Environment->addStaticText(spec.flabel.c_str(), rect, false, false, this, spec.fid);
-		m_fields.push_back(spec);
 		return;
 	}
 	errorstream<< "Invalid label element(" << parts.size() << "): '" << element << "'"  << std::endl;
@@ -1288,21 +1232,15 @@ void GUIFormSpecMenu::parseVertLabel(parserData* data,std::string element)
 		pos.X += stof(v_pos[0]) * (float)spacing.X;
 		pos.Y += stof(v_pos[1]) * (float)spacing.Y;
 
-		gui::IGUIFont *font = NULL;
-				gui::IGUISkin* skin = Environment->getSkin();
-				if (skin)
-					font = skin->getFont();
-
 		core::rect<s32> rect = core::rect<s32>(
 				pos.X, pos.Y+((imgsize.Y/2)- m_btn_height),
 				pos.X+15, pos.Y +
-					(font->getKerningHeight() +
-					font->getDimension(text.c_str()).Height)
+					font_line_height(m_font)
 					* (text.length()+1)
 					+((imgsize.Y/2)- m_btn_height));
 		//actually text.length() would be correct but adding +1 avoids to break all mods
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of label without a size[] element"<<std::endl;
 
 		std::wstring label = L"";
@@ -1368,7 +1306,7 @@ void GUIFormSpecMenu::parseImageButton(parserData* data,std::string element,
 
 		core::rect<s32> rect = core::rect<s32>(pos.X, pos.Y, pos.X+geom.X, pos.Y+geom.Y);
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of image_button without a size[] element"<<std::endl;
 
 		image_name = unescape_string(image_name);
@@ -1452,7 +1390,7 @@ void GUIFormSpecMenu::parseTabHeader(parserData* data,std::string element)
 		pos.X += stof(v_pos[0]) * (float)spacing.X;
 		pos.Y += stof(v_pos[1]) * (float)spacing.Y - m_btn_height * 2;
 		v2s32 geom;
-		geom.X = data->screensize.Y;
+		geom.X = DesiredRect.getWidth();
 		geom.Y = m_btn_height*2;
 
 		core::rect<s32> rect = core::rect<s32>(pos.X, pos.Y, pos.X+geom.X,
@@ -1519,7 +1457,7 @@ void GUIFormSpecMenu::parseItemImageButton(parserData* data,std::string element)
 
 		core::rect<s32> rect = core::rect<s32>(pos.X, pos.Y, pos.X+geom.X, pos.Y+geom.Y);
 
-		if(data->bp_set != 2)
+		if(!data->explicit_size)
 			errorstream<<"WARNING: invalid use of item_image_button without a size[] element"<<std::endl;
 
 		IItemDefManager *idef = m_gamedef->idef();
@@ -1683,6 +1621,30 @@ bool GUIFormSpecMenu::parseVersionDirect(std::string data)
 	return false;
 }
 
+bool GUIFormSpecMenu::parseSizeDirect(parserData* data, std::string element)
+{
+	if (element == "")
+		return false;
+
+	std::vector<std::string> parts = split(element,'[');
+
+	if (parts.size() < 2)
+		return false;
+
+	std::string type = trim(parts[0]);
+	std::string description = trim(parts[1]);
+
+	if (type != "size" && type != "invsize")
+		return false;
+
+	if (type == "invsize")
+		log_deprecated("Deprecated formspec element \"invsize\" is used");
+
+	parseSize(data, description);
+
+	return true;
+}
+
 void GUIFormSpecMenu::parseElement(parserData* data, std::string element)
 {
 	//some prechecks
@@ -1708,17 +1670,6 @@ void GUIFormSpecMenu::parseElement(parserData* data, std::string element)
 	std::string type = trim(parts[0]);
 	std::string description = trim(parts[1]);
 
-	if (type == "size") {
-		parseSize(data,description);
-		return;
-	}
-
-	if (type == "invsize") {
-		log_deprecated("Deprecated formspec element \"invsize\" is used");
-		parseSize(data,description);
-		return;
-	}
-
 	if (type == "list") {
 		parseList(data,description);
 		return;
@@ -1849,14 +1800,6 @@ void GUIFormSpecMenu::regenerateGui(v2u32 screensize)
 		return;
 	}
 
-	gui::IGUIFont *font = NULL;
-			gui::IGUISkin* skin = Environment->getSkin();
-			if (skin)
-				font = skin->getFont();
-
-	m_btn_height = font->getDimension(L"Some unimportant test String").Height;
-	assert(m_btn_height > 0);
-
 	parserData mydata;
 
 	//preserve tables
@@ -1895,12 +1838,6 @@ void GUIFormSpecMenu::regenerateGui(v2u32 screensize)
 	// Base position of contents of form
 	mydata.basepos = getBasePos();
 
-	// State of basepos, 0 = not set, 1= set by formspec, 2 = set by size[] element
-	// Used to adjust form size automatically if needed
-	// A proceed button is added if there is no size[] element
-	mydata.bp_set = 0;
-
-
 	/* Convert m_init_draw_spec to m_inventorylists */
 
 	m_inventorylists.clear();
@@ -1954,13 +1891,132 @@ void GUIFormSpecMenu::regenerateGui(v2u32 screensize)
 		}
 	}
 
+	/* we need size first in order to calculate image scale */
+	mydata.explicit_size = false;
+	for (; i< elements.size(); i++) {
+		if (!parseSizeDirect(&mydata, elements[i])) {
+			break;
+		}
+	}
+
+	if (mydata.explicit_size) {
+		// compute scaling for specified form size
+		if (m_lock) {
+			v2u32 current_screensize = m_device->getVideoDriver()->getScreenSize();
+			v2u32 delta = current_screensize - m_lockscreensize;
+
+			if (current_screensize.Y > m_lockscreensize.Y)
+				delta.Y /= 2;
+			else
+				delta.Y = 0;
+
+			if (current_screensize.X > m_lockscreensize.X)
+				delta.X /= 2;
+			else
+				delta.X = 0;
+
+			offset = v2s32(delta.X,delta.Y);
+
+			mydata.screensize = m_lockscreensize;
+		} else {
+			offset = v2s32(0,0);
+		}
+
+		double gui_scaling = g_settings->getFloat("gui_scaling");
+		double screen_dpi = porting::getDisplayDensity() * 96;
+
+		double use_imgsize;
+		if (m_lock) {
+			// In fixed-size mode, inventory image size
+			// is 0.53 inch multiplied by the gui_scaling
+			// config parameter.  This magic size is chosen
+			// to make the main menu (15.5 inventory images
+			// wide, including border) just fit into the
+			// default window (800 pixels wide) at 96 DPI
+			// and default scaling (1.00).
+			use_imgsize = 0.53 * screen_dpi * gui_scaling;
+		} else {
+			// In variable-size mode, we prefer to make the
+			// inventory image size 1/15 of screen height,
+			// multiplied by the gui_scaling config parameter.
+			// If the preferred size won't fit the whole
+			// form on the screen, either horizontally or
+			// vertically, then we scale it down to fit.
+			// (The magic numbers in the computation of what
+			// fits arise from the scaling factors in the
+			// following stanza, including the form border,
+			// help text space, and 0.1 inventory slot spare.)
+			// However, a minimum size is also set, that
+			// the image size can't be less than 0.3 inch
+			// multiplied by gui_scaling, even if this means
+			// the form doesn't fit the screen.
+			double prefer_imgsize = mydata.screensize.Y / 15 *
+							gui_scaling;
+			double fitx_imgsize = mydata.screensize.X /
+				((5.0/4.0) * (0.5 + mydata.invsize.X));
+			double fity_imgsize = mydata.screensize.Y /
+				((15.0/13.0) * (0.85 * mydata.invsize.Y));
+			double screen_dpi = porting::getDisplayDensity() * 96;
+			double min_imgsize = 0.3 * screen_dpi * gui_scaling;
+			use_imgsize = MYMAX(min_imgsize, MYMIN(prefer_imgsize,
+				MYMIN(fitx_imgsize, fity_imgsize)));
+		}
+
+		// Everything else is scaled in proportion to the
+		// inventory image size.  The inventory slot spacing
+		// is 5/4 image size horizontally and 15/13 image size
+		// vertically.	The padding around the form (incorporating
+		// the border of the outer inventory slots) is 3/8
+		// image size.	Font height (baseline to baseline)
+		// is 2/5 vertical inventory slot spacing, and button
+		// half-height is 7/8 of font height.
+		imgsize = v2s32(use_imgsize, use_imgsize);
+		spacing = v2s32(use_imgsize*5.0/4, use_imgsize*15.0/13);
+		padding = v2s32(use_imgsize*3.0/8, use_imgsize*3.0/8);
+		double target_font_height = use_imgsize*15.0/13 * 0.4;
+		m_btn_height = use_imgsize*15.0/13 * 0.35;
+
+		m_font = select_font_by_line_height(target_font_height);
+
+		mydata.size = v2s32(
+			padding.X*2+spacing.X*(mydata.invsize.X-1.0)+imgsize.X,
+			padding.Y*2+spacing.Y*(mydata.invsize.Y-1.0)+imgsize.Y + m_btn_height*2.0/3.0
+		);
+		DesiredRect = mydata.rect = core::rect<s32>(
+				mydata.screensize.X/2 - mydata.size.X/2 + offset.X,
+				mydata.screensize.Y/2 - mydata.size.Y/2 + offset.Y,
+				mydata.screensize.X/2 + mydata.size.X/2 + offset.X,
+				mydata.screensize.Y/2 + mydata.size.Y/2 + offset.Y
+		);
+	} else {
+		// Non-size[] form must consist only of text fields and
+		// implicit "Proceed" button.  Use default font, and
+		// temporary form size which will be recalculated below.
+		m_font = glb_fontengine->getFont();
+		m_btn_height = font_line_height(m_font) * 0.875;
+		DesiredRect = core::rect<s32>(
+			mydata.screensize.X/2 - 580/2,
+			mydata.screensize.Y/2 - 300/2,
+			mydata.screensize.X/2 + 580/2,
+			mydata.screensize.Y/2 + 300/2
+		);
+	}
+	recalculateAbsolutePosition(false);
+	mydata.basepos = getBasePos();
+	m_tooltip_element->setOverrideFont(m_font);
+
+	gui::IGUISkin* skin = Environment->getSkin();
+	assert(skin != NULL);
+	gui::IGUIFont *old_font = skin->getFont();
+	skin->setFont(m_font);
+
 	for (; i< elements.size(); i++) {
 		parseElement(&mydata, elements[i]);
 	}
 
-	// If there's fields, add a Proceed button
-	if (m_fields.size() && mydata.bp_set != 2) {
-		// if the size wasn't set by an invsize[] or size[] adjust it now to fit all the fields
+	// If there are fields without explicit size[], add a "Proceed"
+	// button and adjust size to fit all the fields.
+	if (m_fields.size() && !mydata.explicit_size) {
 		mydata.rect = core::rect<s32>(
 				mydata.screensize.X/2 - 580/2,
 				mydata.screensize.Y/2 - 300/2,
@@ -1992,6 +2048,8 @@ void GUIFormSpecMenu::regenerateGui(v2u32 screensize)
 			|| !isMyChild(focused_element)
 			|| focused_element->getType() == gui::EGUIET_TAB_CONTROL)
 		setInitialFocus();
+
+	skin->setFont(old_font);
 }
 
 #ifdef __ANDROID__
@@ -2068,11 +2126,6 @@ void GUIFormSpecMenu::drawList(const ListDrawSpec &s, int phase)
 {
 	video::IVideoDriver* driver = Environment->getVideoDriver();
 
-	gui::IGUIFont *font = NULL;
-	gui::IGUISkin* skin = Environment->getSkin();
-	if (skin)
-		font = skin->getFont();
-
 	Inventory *inv = m_invmgr->getInventory(s.inventoryloc);
 	if(!inv){
 		infostream<<"GUIFormSpecMenu::drawList(): WARNING: "
@@ -2149,7 +2202,7 @@ void GUIFormSpecMenu::drawList(const ListDrawSpec &s, int phase)
 			}
 			if(!item.empty())
 			{
-				drawItemStack(driver, font, item,
+				drawItemStack(driver, m_font, item,
 						rect, &AbsoluteClippingRect, m_gamedef);
 			}
 
@@ -2183,12 +2236,6 @@ void GUIFormSpecMenu::drawSelectedItem()
 
 	video::IVideoDriver* driver = Environment->getVideoDriver();
 
-	// Get font
-	gui::IGUIFont *font = NULL;
-	gui::IGUISkin* skin = Environment->getSkin();
-	if (skin)
-		font = skin->getFont();
-
 	Inventory *inv = m_invmgr->getInventory(m_selected_item->inventoryloc);
 	assert(inv);
 	InventoryList *list = inv->getList(m_selected_item->listname);
@@ -2198,7 +2245,7 @@ void GUIFormSpecMenu::drawSelectedItem()
 
 	core::rect<s32> imgrect(0,0,imgsize.X,imgsize.Y);
 	core::rect<s32> rect = imgrect + (m_pointer - imgrect.getCenter());
-	drawItemStack(driver, font, stack, rect, NULL, m_gamedef);
+	drawItemStack(driver, m_font, stack, rect, NULL, m_gamedef);
 }
 
 void GUIFormSpecMenu::drawMenu()
@@ -2211,6 +2258,11 @@ void GUIFormSpecMenu::drawMenu()
 		}
 	}
 
+	gui::IGUISkin* skin = Environment->getSkin();
+	assert(skin != NULL);
+	gui::IGUIFont *old_font = skin->getFont();
+	skin->setFont(m_font);
+
 	updateSelectedItem();
 
 	video::IVideoDriver* driver = Environment->getVideoDriver();
@@ -2409,6 +2461,8 @@ void GUIFormSpecMenu::drawMenu()
 		Draw dragged item stack
 	*/
 	drawSelectedItem();
+
+	skin->setFont(old_font);
 }
 
 void GUIFormSpecMenu::updateSelectedItem()
@@ -2665,6 +2719,30 @@ static bool isChild(gui::IGUIElement * tocheck, gui::IGUIElement * parent)
 
 bool GUIFormSpecMenu::preprocessEvent(const SEvent& event)
 {
+	// The IGUITabControl renders visually using the skin's selected
+	// font, which we override for the duration of form drawing,
+	// but computes tab hotspots based on how it would have rendered
+	// using the font that is selected at the time of button release.
+	// To make these two consistent, temporarily override the skin's
+	// font while the IGUITabControl is processing the event.
+	if (event.EventType == EET_MOUSE_INPUT_EVENT &&
+			event.MouseInput.Event == EMIE_LMOUSE_LEFT_UP) {
+		s32 x = event.MouseInput.X;
+		s32 y = event.MouseInput.Y;
+		gui::IGUIElement *hovered =
+			Environment->getRootGUIElement()->getElementFromPoint(
+				core::position2d<s32>(x, y));
+		if (hovered->getType() == gui::EGUIET_TAB_CONTROL) {
+			gui::IGUISkin* skin = Environment->getSkin();
+			assert(skin != NULL);
+			gui::IGUIFont *old_font = skin->getFont();
+			skin->setFont(m_font);
+			bool retval = hovered->OnEvent(event);
+			skin->setFont(old_font);
+			return retval;
+		}
+	}
+
 	// Fix Esc/Return key being eaten by checkboxen and tables
 	if(event.EventType==EET_KEY_INPUT_EVENT) {
 		KeyPress kp(event.KeyInput);
diff --git a/src/guiFormSpecMenu.h b/src/guiFormSpecMenu.h
index df988f5a5..455aeaab8 100644
--- a/src/guiFormSpecMenu.h
+++ b/src/guiFormSpecMenu.h
@@ -348,10 +348,11 @@ private:
 	unsigned int      m_formspec_version;
 
 	typedef struct {
+		bool explicit_size;
+		v2f invsize;
 		v2s32 size;
 		core::rect<s32> rect;
 		v2s32 basepos;
-		int bp_set;
 		v2u32 screensize;
 		std::wstring focused_fieldname;
 		GUITable::TableOptions table_options;
@@ -398,6 +399,7 @@ private:
 	void parseListColors(parserData* data,std::string element);
 	void parseTooltip(parserData* data,std::string element);
 	bool parseVersionDirect(std::string data);
+	bool parseSizeDirect(parserData* data, std::string element);
 	void parseScrollBar(parserData* data, std::string element);
 
 	/**
@@ -415,6 +417,7 @@ private:
 	clickpos m_doubleclickdetect[2];
 
 	int m_btn_height;
+	gui::IGUIFont *m_font;
 
 	std::wstring getLabelByID(s32 id);
 	std::wstring getNameByID(s32 id);