gui: make debug windows right edge sticky

Now when the right edge of any debug window in the list is at the edge
of the viewport width, it will stick there through resizes.

There's a bug where if the resize change is enough to "capture" a window
that wasn't intended to be sticky it will capture. Given this didn't
happen much during testing, I don't think the extra state + code
required is worth it for these windows.

browser/gui/app.cpp

@@ -17,6 +17,7 @@
 #include <imgui-SFML.h>
 #include <imgui.h>
 #include <imgui_stdlib.h>
+#include <imgui_internal.h>
 #include <spdlog/spdlog.h>
 
 #include <algorithm>
@@ -134,6 +135,8 @@ App::App(std::string browser_title, std::string start_page_hint, bool load_start
     engine_.set_on_page_loaded(std::bind_front(&App::on_page_loaded, this));
     engine_.set_on_layout_updated(std::bind_front(&App::on_layout_updated, this));
 
+    prev_sticky_w = 0;
+
     if (load_start_page) {
         ensure_has_scheme(url_buf_);
         navigate();
@@ -159,6 +162,20 @@ void App::set_scale(unsigned scale) {
     engine_.set_layout_width(windowSize.x / scale_);
 }
 
+void App::sticky_windows(const sf::Event::SizeEvent &size) {
+    int delta = prev_sticky_w - size.width;
+    for (ImGuiWindow *win  : GImGui->Windows) {
+        if (!win) {
+            continue;
+        }
+        int edge = static_cast<int>(win->Pos.x) + static_cast<int>(win->Size.x);
+        if (edge == prev_sticky_w) {
+            ImGui::SetWindowPos(win, {win->Pos.x - delta, win->Pos.y});
+        }
+    }
+    prev_sticky_w = size.width;
+}
+
 int App::run() {
     while (window_.isOpen()) {
         sf::Event event;
@@ -173,6 +190,7 @@ int App::run() {
                 case sf::Event::Resized: {
                     canvas_->set_viewport_size(event.size.width, event.size.height);
                     engine_.set_layout_width(event.size.width / scale_);
+                    sticky_windows(event.size);
                     break;
                 }
                 case sf::Event::KeyPressed: {

browser/gui/app.h

@@ -17,6 +17,7 @@
 #include <SFML/Graphics/RenderWindow.hpp>
 #include <SFML/System/Clock.hpp>
 #include <SFML/Window/Cursor.hpp>
+#include <SFML/Window/Event.hpp>
 
 #include <memory>
 #include <string>
@@ -74,6 +75,8 @@ class App final {
 
     void navigate();
     void layout();
+    void sticky_windows(const sf::Event::SizeEvent &);
+    int prev_sticky_w;
 
     std::vector<dom::Node const *> get_hovered_nodes(geom::Position document_position) const;
     geom::Position to_document_position(geom::Position window_position) const;