Add concept of size increments to windowing system.

Use this to implement incremental resizing for Terminal so that we only
ever resize to fit a perfect number of rows and columns.

This is very nice. :^)

WindowServer/WSAPITypes.h

@@ -170,6 +170,8 @@ struct WSAPI_ClientMessage {
             WSAPI_Rect rect;
             bool has_alpha_channel;
             float opacity;
+            WSAPI_Size base_size;
+            WSAPI_Size size_increment;
         } window;
         struct {
             WSAPI_Size size;

WindowServer/WSClientConnection.cpp

@@ -319,6 +319,7 @@ void WSClientConnection::handle_request(WSAPICreateWindowRequest& request)
     window->set_title(request.title());
     window->set_rect(request.rect());
     window->set_opacity(request.opacity());
+    window->set_size_increment(request.size_increment());
     m_windows.set(window_id, move(window));
     WSAPI_ServerMessage response;
     response.type = WSAPI_ServerMessage::Type::DidCreateWindow;

WindowServer/WSMessage.h

@@ -349,12 +349,14 @@ private:
 
 class WSAPICreateWindowRequest : public WSAPIClientRequest {
 public:
-    WSAPICreateWindowRequest(int client_id, const Rect& rect, const String& title, bool has_alpha_channel, float opacity)
+    WSAPICreateWindowRequest(int client_id, const Rect& rect, const String& title, bool has_alpha_channel, float opacity, const Size& base_size, const Size& size_increment)
         : WSAPIClientRequest(WSMessage::APICreateWindowRequest, client_id)
         , m_rect(rect)
         , m_title(title)
         , m_opacity(opacity)
         , m_has_alpha_channel(has_alpha_channel)
+        , m_base_size(base_size)
+        , m_size_increment(size_increment)
     {
     }
 
@@ -362,12 +364,16 @@ public:
     String title() const { return m_title; }
     bool has_alpha_channel() const { return m_has_alpha_channel; }
     float opacity() const { return m_opacity; }
+    Size size_increment() const { return m_size_increment; }
+    Size base_size() const { return m_base_size; }
 
 private:
     Rect m_rect;
     String m_title;
     float m_opacity { 0 };
     bool m_has_alpha_channel { false };
+    Size m_size_increment;
+    Size m_base_size;
 };
 
 class WSAPIDestroyWindowRequest : public WSAPIClientRequest {

WindowServer/WSMessageLoop.cpp

@@ -302,7 +302,7 @@ void WSMessageLoop::on_receive_from_client(int client_id, const WSAPI_ClientMess
         break;
     case WSAPI_ClientMessage::Type::CreateWindow:
         ASSERT(message.text_length < sizeof(message.text));
-        post_message(client, make<WSAPICreateWindowRequest>(client_id, message.window.rect, String(message.text, message.text_length), message.window.has_alpha_channel, message.window.opacity));
+        post_message(client, make<WSAPICreateWindowRequest>(client_id, message.window.rect, String(message.text, message.text_length), message.window.has_alpha_channel, message.window.opacity, message.window.base_size, message.window.size_increment));
         break;
     case WSAPI_ClientMessage::Type::DestroyWindow:
         post_message(client, make<WSAPIDestroyWindowRequest>(client_id, message.window_id));

WindowServer/WSWindow.h

@@ -70,6 +70,12 @@ public:
     bool has_painted_since_last_resize() const { return m_has_painted_since_last_resize; }
     void set_has_painted_since_last_resize(bool b) { m_has_painted_since_last_resize = b; }
 
+    Size size_increment() const { return m_size_increment; }
+    void set_size_increment(const Size& increment) { m_size_increment = increment; }
+
+    Size base_size() const { return m_base_size; }
+    void set_base_size(const Size& size) { m_base_size = size; }
+
     // For InlineLinkedList.
     // FIXME: Maybe make a ListHashSet and then WSWindowManager can just use that.
     WSWindow* m_next { nullptr };
@@ -89,4 +95,6 @@ private:
     int m_window_id { -1 };
     float m_opacity { 1 };
     Rect m_last_lazy_resize_rect;
+    Size m_size_increment;
+    Size m_base_size;
 };

WindowServer/WSWindowManager.cpp

@@ -548,6 +548,14 @@ void WSWindowManager::process_mouse_event(WSMouseEvent& event, WSWindow*& event_
             auto new_rect = m_resize_window_original_rect;
             new_rect.set_width(max(50, new_rect.width() + dx));
             new_rect.set_height(max(50, new_rect.height() + dy));
+
+            if (!m_resize_window->size_increment().is_null()) {
+                int horizontal_incs = (new_rect.width() - m_resize_window->base_size().width()) / m_resize_window->size_increment().width();
+                new_rect.set_width(m_resize_window->base_size().width() + horizontal_incs * m_resize_window->size_increment().width());
+                int vertical_incs = (new_rect.height() - m_resize_window->base_size().height()) / m_resize_window->size_increment().height();
+                new_rect.set_height(m_resize_window->base_size().height() + vertical_incs * m_resize_window->size_increment().height());
+            }
+
             if (m_resize_window->rect() == new_rect)
                 return;
 #ifdef RESIZE_DEBUG