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

@@ -16,6 +16,7 @@
 #include <imgui-SFML.h>
 #include <imgui.h>
 #include <imgui_stdlib.h>
+#include <imgui_internal.h>
 #include <spdlog/spdlog.h>
 
 #include <cmath>
@@ -156,6 +157,35 @@ void App::set_scale(unsigned scale) {
     engine_.set_layout_width(windowSize.x / scale_);
 }
 
+void App::sticky_windows(sf::Event::SizeEvent size) {
+    const char *names[] = {
+        "Navigation",
+        "HTTP Response",
+        "DOM",
+        "Stylesheet",
+        "Layout",
+        NULL,
+    };
+
+    int delta = k_width - size.width;
+    for (uint8_t i = 0;; ++i) {
+        const char *name = names[i];
+        if (!name) {
+            break;
+        }
+        ImGuiWindow *win = ImGui::FindWindowByName(name);
+        if (!win) {
+            continue;
+        }
+        int edge = win->Pos.x + win->Size.x;
+        if (edge == k_width) {
+            ImGui::SetWindowPos(name, {win->Pos.x - delta, win->Pos.y});
+        }
+    }
+    k_width = size.width;
+    k_height = size.height;
+}
+
 int App::run() {
     while (window_.isOpen()) {
         sf::Event event;
@@ -170,6 +200,7 @@ 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

@@ -14,6 +14,7 @@
 #include "uri/uri.h"
 #include "util/history.h"
 
+#include <SFML/Window/Event.hpp>
 #include <SFML/Graphics/RenderWindow.hpp>
 #include <SFML/System/Clock.hpp>
 #include <SFML/Window/Cursor.hpp>
@@ -74,7 +75,9 @@ class App final {
 
     void navigate();
     void layout();
-
+    void sticky_windows(sf::Event::SizeEvent);
+    int k_width, k_height;
+
     std::vector<dom::Node const *> get_hovered_nodes(geom::Position document_position) const;
     geom::Position to_document_position(geom::Position window_position) const;