Notabilis has proposed merging 
lp:~widelands-dev/widelands/bug-1751620-floating-images into lp:widelands.

Commit message:
Implementing text floating around images.

Requested reviews:
  GunChleoc (gunchleoc)
Related bugs:
  Bug #1751620 in widelands: "Bring back floating images in font renderer"
  https://bugs.launchpad.net/widelands/+bug/1751620

For more details, see:
https://code.launchpad.net/~widelands-dev/widelands/bug-1751620-floating-images/+merge/341286

Implements a richtext attribute to allow text to flow around images.
-- 
Your team Widelands Developers is subscribed to branch 
lp:~widelands-dev/widelands/bug-1751620-floating-images.
=== modified file 'data/scripting/richtext.lua'
--- data/scripting/richtext.lua	2018-02-24 15:31:26 +0000
+++ data/scripting/richtext.lua	2018-03-11 16:52:13 +0000
@@ -419,9 +419,8 @@
 function li_image(imagepath, text)
    return
       div("width=100%",
-         div(p(vspace(6) .. img(imagepath) .. space(6))) ..
-         div(p(space(6))) ..
-         div("width=*", p(vspace(6) .. text .. vspace(12)))
+		div("float=left padding_r=6", p(img(imagepath))) ..
+         p(text)
       )
 end
 

=== modified file 'src/graphic/text/rt_parse.cc'
--- src/graphic/text/rt_parse.cc	2018-02-25 11:51:29 +0000
+++ src/graphic/text/rt_parse.cc	2018-03-11 16:52:13 +0000
@@ -261,8 +261,9 @@
 
 The same attributes as :ref:`rt_tags_rt`, plus the following:
 
-* **margin**: Shrink all contents to leave a margin towards the outer edge of this tag's rectangle
-* **float**: To be implemented. Allowed values are ``left``,  ``right``
+* **margin**: Shrink all contents to leave a margin towards the outer edge of this tag's rectangle.
+* **float**: Make text float around this div. Allowed values are ``left``,  ``right``. Structure has to be
+  something like: ``div("width=100%", div("float=left padding_r=6", p(img(imagepath))) .. p(text))``
 * **valign**: Align the contents vertically. Allowed values are ``top`` (default), ``center`` or ``middle``, ``bottom``.
 * **width**: The width of this element, as a pixel amount, or as a percentage.
   The last ``div`` in a row can be expanded automatically by using ``*``.

=== modified file 'src/graphic/text/rt_render.cc'
--- src/graphic/text/rt_render.cc	2018-02-25 18:20:58 +0000
+++ src/graphic/text/rt_render.cc	2018-03-11 16:52:13 +0000
@@ -292,6 +292,9 @@
 	int32_t x_, y_;
 };
 
+/*
+ * Class to calculate positions of nodes within a div tag.
+ */
 class Layout {
 public:
 	explicit Layout(std::vector<std::shared_ptr<RenderNode>>& all)
@@ -307,19 +310,7 @@
 	fit_nodes(std::vector<std::shared_ptr<RenderNode>>* rv, uint16_t w, Borders p, bool trim_spaces);
 
 private:
-	// Represents a change in the rendering constraints. For example when an
-	// Image is inserted, the width will become wider after it. This is a
-	// constraint change.
-	struct ConstraintChange {
-		int at_y;
-		int32_t delta_w;
-		int32_t delta_offset_x;
-
-		bool operator<(const ConstraintChange& o) const {
-			return at_y > o.at_y || (at_y == o.at_y && delta_w > o.delta_w);
-		}
-	};
-
+	bool calculate_line_width(uint16_t *x, uint16_t *w, uint16_t lineheight);
 	uint16_t fit_line(uint16_t w,
 	                  const Borders&,
 	                  std::vector<std::shared_ptr<RenderNode>>* rv,
@@ -328,13 +319,55 @@
 	uint16_t h_;
 	size_t idx_;
 	std::vector<std::shared_ptr<RenderNode>>& all_nodes_;
-	std::priority_queue<ConstraintChange> constraint_changes_;
+	std::queue<std::shared_ptr<RenderNode>> floats_;
 };
 
-uint16_t Layout::fit_line(uint16_t w,
-                          const Borders& p,
-                          std::vector<std::shared_ptr<RenderNode>>* rv,
-                          bool trim_spaces) {
+/**
+ * Calculate the width of a line at h_ taking into account floating elements.
+ * @param x The first useable x position in the line. Has to be set by the caller,
+ *          might be modified inside this function.
+ * @param x The useable width of the line. Has to be set by the caller,
+ *          might be modified inside this function.
+ * @param lineheight The height of the line the maximum width should be calculated of.
+ * @return Whether less than the full width can be used (i.e., there is a float).
+ */
+bool Layout::calculate_line_width(uint16_t *x, uint16_t *w, uint16_t lineheight) {
+	// Drop elements we already passed
+	while (!floats_.empty() && h_ >= floats_.front()->y() + floats_.front()->height()) {
+			floats_.pop();
+	}
+	if (floats_.empty()) {
+		return false;
+	}
+	// Check whether there is an element at the current height
+	std::shared_ptr<RenderNode> n = floats_.front();
+	if (h_ + lineheight < n->y()) {
+		// Nope, nothing in the current line
+		// Since the elements are ordered, no further element can match
+		return false;
+	}
+
+	if (n->get_floating() == RenderNode::FLOAT_LEFT) {
+		*x += n->width();
+	} else {
+		assert(n->get_floating() == RenderNode::FLOAT_RIGHT);
+		*w -= n->width();
+	}
+	return true;
+}
+
+/*
+ * Calculate x positions of nodes in one line and return them in rv.
+ * As many nodes of all_nodes_ are added to the line as there is space.
+ * Remove leading/trailing spaces and assign x positions to all elements.
+ * Use remaining space to distribute expanding elements a bit further.
+ * Returns hotspot of the line.
+ * Method is called from within Layout::fit_nodes().
+ */
+uint16_t Layout::fit_line(const uint16_t w_max, // Maximum width of line
+                          const Borders& p, // Left/right border. Is left empty
+                          std::vector<std::shared_ptr<RenderNode>>* rv, // Output: Nodes to render
+                          bool trim_spaces) { // Whether leading/trailing space should be removed
 	assert(rv->empty());
 
 	// Remove leading spaces
@@ -342,17 +375,79 @@
 		all_nodes_[idx_++].reset();
 	}
 
-	uint16_t x = p.left;
+	uint16_t w;
+	uint16_t x;
 	std::size_t first_idx = idx_;
+	uint16_t lineheight = 0;
+
+	// Pass 1: Run through all nodes who *might* end up in this line and check for floats
+	w = w_max - p.right;
+	x = p.left;
+	bool reduced_width = calculate_line_width(&x, &w, lineheight);
+	lineheight = 0;
+	uint16_t w_used = 0;
+	for (; idx_ < all_nodes_.size(); ++idx_) {
+		if (w_used + all_nodes_[idx_]->width() > w) {
+			// Line is full
+			break;
+		}
+		if (all_nodes_[idx_]->get_floating() == RenderNode::NO_FLOAT) {
+			// Normal, non-floating node
+			w_used += all_nodes_[idx_]->width();
+			assert(all_nodes_[idx_]->height() >= all_nodes_[idx_]->hotspot_y());
+			lineheight = std::max(lineheight, all_nodes_[idx_]->height());
+			continue;
+		}
+		// Found a float. Add it to list
+		// New float start directly below lowest flow in list
+		if (!floats_.empty()) {
+			all_nodes_[idx_]->set_y(floats_.back()->y() + floats_.back()->height());
+		} else {
+			all_nodes_[idx_]->set_y(h_);
+		}
+		// Set x position of the float based on its desired orientation
+		if (all_nodes_[idx_]->get_floating() == RenderNode::FLOAT_LEFT) {
+			all_nodes_[idx_]->set_x(p.left);
+		} else {
+			assert(all_nodes_[idx_]->get_floating() == RenderNode::FLOAT_RIGHT);
+			all_nodes_[idx_]->set_x(w_max - all_nodes_[idx_]->width() - p.right);
+		}
+		floats_.push(all_nodes_[idx_]);
+		// When the line width hasn't been reduced by a float yet, do so now.
+		// If it already has been reduced than the new float will be placed somewhere below
+		// the current line so no need to adapt the line width
+		if (!reduced_width) {
+			// Don't need to reset x and w since they haven't been modified on last call
+			reduced_width = calculate_line_width(&x, &w, lineheight);
+			assert(reduced_width);
+		}
+	}
+
+	idx_ = first_idx;
+	// w and x now contain the width of the line and the x position of the first element in it
 
 	// Calc fitting nodes
 	while (idx_ < all_nodes_.size()) {
 		std::shared_ptr<RenderNode> n = all_nodes_[idx_];
+		if (n->get_floating() != RenderNode::NO_FLOAT) {
+			// Don't handle floaters here
+			rv->push_back(n);
+			if (idx_ == first_idx) {
+				first_idx++;
+			}
+			++idx_;
+			continue;
+		}
 		uint16_t nw = n->width();
-		if (x + nw + p.right > w || n->get_floating() != RenderNode::NO_FLOAT) {
+		// Check whether the element is too big for the current line
+		// (position + width-of-element + border) > width-of-line
+		if (x + nw + p.right > w) {
+			// Its too big
 			if (idx_ == first_idx) {
+				// If it is the first element in the line, add it anyway and pretend that it matches exactly
 				nw = w - p.right - x;
 			} else {
+				// Too width and not the first element: We are done with the line
 				break;
 			}
 		}
@@ -401,9 +496,12 @@
 		}
 	}
 
-	// Find the biggest hotspot of the truly remaining items.
+	// Find the biggest hotspot of the truly remaining non-floating items.
 	uint16_t cur_line_hotspot = 0;
 	for (std::shared_ptr<RenderNode> node : *rv) {
+		if (node->get_floating() != RenderNode::NO_FLOAT) {
+			continue;
+		}
 		cur_line_hotspot = std::max(cur_line_hotspot, node->hotspot_y());
 	}
 	return cur_line_hotspot;
@@ -412,6 +510,9 @@
 /*
  * Take ownership of all nodes, delete those that we do not render anyways (for
  * example unneeded spaces), append the rest to the vector we got.
+ * Also, calculate positions for all nodes based on the given width w
+ * and the widths of the nodes.
+ * Method is called from within DivTagHandler::enter().
  */
 uint16_t Layout::fit_nodes(std::vector<std::shared_ptr<RenderNode>>* rv,
                            uint16_t w,
@@ -428,10 +529,12 @@
 
 		int line_height = 0;
 		int line_start = INFINITE_WIDTH;
-		// Compute real line height and width, taking into account alignement
+		// Compute real line height and width, taking into account alignment
 		for (std::shared_ptr<RenderNode> n : nodes_in_line) {
-			line_height = std::max(line_height, biggest_hotspot - n->hotspot_y() + n->height());
-			n->set_y(h_ + biggest_hotspot - n->hotspot_y());
+			if (n->get_floating() == RenderNode::NO_FLOAT) {
+				line_height = std::max(line_height, biggest_hotspot - n->hotspot_y() + n->height());
+				n->set_y(h_ + biggest_hotspot - n->hotspot_y());
+			}
 			if (line_start >= INFINITE_WIDTH || n->x() < line_start) {
 				line_start = n->x() - p.left;
 			}
@@ -440,7 +543,7 @@
 
 		// Go over again and adjust position for VALIGN
 		for (std::shared_ptr<RenderNode> n : nodes_in_line) {
-			uint16_t space = line_height - n->height();
+			int space = line_height - n->height();
 			if (!space || n->valign() == UI::Align::kBottom) {
 				continue;
 			}
@@ -450,43 +553,25 @@
 			// Space can become negative, for example when we have mixed fontsets on the same line
 			// (e.g. "default" and "arabic"), due to differing font heights and hotspots.
 			// So, we fix the sign.
-			n->set_y(std::abs(n->y() - space));
+			if (n->get_floating() == RenderNode::NO_FLOAT) {
+				n->set_y(std::abs(n->y() - space));
+			}
 		}
 		rv->insert(rv->end(), nodes_in_line.begin(), nodes_in_line.end());
 
 		h_ += line_height;
-		while (!constraint_changes_.empty() && constraint_changes_.top().at_y <= h_) {
-			const ConstraintChange& top = constraint_changes_.top();
-			w += top.delta_w;
-			p.left += top.delta_offset_x;
-			constraint_changes_.pop();
-		}
 
-		if ((idx_ < all_nodes_.size()) && all_nodes_[idx_]->get_floating()) {
-			std::shared_ptr<RenderNode> n = all_nodes_[idx_];
-			n->set_y(h_);
-			ConstraintChange cc = {h_ + n->height(), 0, 0};
-			if (n->get_floating() == RenderNode::FLOAT_LEFT) {
-				n->set_x(p.left);
-				p.left += n->width();
-				cc.delta_offset_x = -n->width();
-				max_line_width = std::max<int>(max_line_width, n->x() + n->width() + p.right);
-			} else {
-				n->set_x(w - n->width() - p.right);
-				w -= n->width();
-				cc.delta_w = n->width();
-				max_line_width = std::max(max_line_width, w);
-			}
-			constraint_changes_.push(cc);
-			rv->push_back(n);
-			++idx_;
-		}
 		if (idx_ == idx_before_iteration_) {
 			throw WidthTooSmall(
 			   "Could not fit a single render node in line. Width of an Element is too small!");
 		}
 	}
 
+	if (!floats_.empty()) {
+		// If there is a float left this means the floats go down further than the text.
+		// If this is the case, reset the height of the div
+		h_ = std::max<uint16_t>(h_, floats_.back()->y() + floats_.back()->height());
+	}
 	h_ += p.bottom;
 	return max_line_width;
 }
@@ -800,6 +885,7 @@
 
 		// Draw Solid background Color
 		if (is_background_color_set_) {
+			// TODO(Notabilis): I think margin_.right and .bottom are missing in next line
 			UI::RenderedRect* bg_rect =
 			   new UI::RenderedRect(Recti(margin_.left, margin_.top, w_, h_), background_color_);
 			// Size is automatically adjusted in RenderedText while blitting, so no need to call
@@ -1336,6 +1422,13 @@
 	     render_node_(new DivTagRenderNode(ns)) {
 	}
 
+	/*
+	 * Calculate width of all children of this div.
+	 * Width is either fixed, a percentage of the parent or fill. If the width should fill
+	 * the line, it is set to the remaining width of the current line. New lines aren't really
+	 * started here but percent/filling elements are made so big that they won't fit into the
+	 * previous line when their final position is calculated in Layout::fit_nodes().
+	 */
 	void enter() override {
 		Borders padding, margin;
 
@@ -1368,26 +1461,24 @@
 		}
 
 		std::vector<std::shared_ptr<RenderNode>> subnodes;
-		// If a percentage width is used, temporarily set it as the overall width. This way, divs with
-		// width "fill" only use the width of their parent node. Also, percentages given in child
-		// nodes
-		// are relative to the width of their parent node.
-		const uint16_t old_overall_width = renderer_style_.overall_width;
+		// If a percentage width is used, temporarily set it as the overall width. This way,
+		// divs with width "fill" only use the width of their parent node. Also, percentages
+		// given in child nodes are relative to the width of their parent node.
+		const uint16_t old_line_width = renderer_style_.overall_width;
 		if (render_node_->desired_width().unit == WidthUnit::kPercent) {
-			renderer_style_.overall_width =
-			   render_node_->desired_width().width * renderer_style_.overall_width / 100;
+			renderer_style_.overall_width = render_node_->desired_width().width * renderer_style_.overall_width / 100;
 		}
 		TagHandler::emit_nodes(subnodes);
-		renderer_style_.overall_width = old_overall_width;
+		renderer_style_.overall_width = old_line_width;
 
-		// Determine the width by the width of the widest subnode
+		// Determine the required width by the width of the widest subnode
 		uint16_t width_first_subnode = INFINITE_WIDTH;
 		uint16_t widest_subnode = 0;
 		for (std::shared_ptr<RenderNode> n : subnodes) {
 			if (n->width() >= INFINITE_WIDTH) {
 				continue;
 			}
-			if (width_first_subnode >= INFINITE_WIDTH && n->width() > 0) {
+			if (width_first_subnode >= INFINITE_WIDTH && n->width()) {
 				width_first_subnode = n->width() + padding.left + padding.right;
 			}
 			widest_subnode = std::max<int>(widest_subnode, n->width() + padding.left + padding.right);
@@ -1401,6 +1492,9 @@
 		case WidthUnit::kPercent:
 			w_ = render_node_->desired_width().width * renderer_style_.overall_width / 100;
 
+			if (render_node_->get_floating() != RenderNode::NO_FLOAT) {
+				break;
+			}
 			// Reduce remaining width
 			if (renderer_style_.remaining_width <= w_) {
 				// Not enough space. Div will be placed in the next line, calculate the remaining space
@@ -1412,7 +1506,9 @@
 			break;
 		case WidthUnit::kFill:
 			w_ = renderer_style_.remaining_width;
-			renderer_style_.remaining_width = 0;
+			if (render_node_->get_floating() == RenderNode::NO_FLOAT) {
+				renderer_style_.remaining_width = 0;
+			}
 			break;
 		default:
 			if (!w_) {
@@ -1430,7 +1526,9 @@
 			extra_width = w_ - max_line_width;
 		} else if (render_node_->desired_width().unit == WidthUnit::kShrink) {
 			w_ = max_line_width;
-			renderer_style_.remaining_width -= w_;
+			if (render_node_->get_floating() == RenderNode::NO_FLOAT) {
+				renderer_style_.remaining_width -= w_;
+			}
 		}
 
 		// Collect all tags from children

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