introduce space key modifier

Pointer movement is ignored when the `space` key is held.

To ensure [Screenshot Tool](https://extensions.gnome.org/extension/1112/screenshot-tool/) extension compatibility, we need a way to let the third extension select the screenshot area with pointer but without leaving drawing mode and without drawing.

As a side effect, it allows to insert straight line segments in free drawing (after releasing the key).

Fixes issue #20

README.md

@@ -25,3 +25,13 @@ Install :
 5. Enable the extension in Gnome-tweak-tool
 6. `Super + Alt + D` to test
 7. [https://framagit.org/abakkk/DrawOnYourScreen/issues](https://framagit.org/abakkk/DrawOnYourScreen/issues) to say it doesn't work
+
+
+Details :
+---------
+
+ * Screenshot Tool extension:
+
+
+ [Screenshot Tool](https://extensions.gnome.org/extension/1112/screenshot-tool/) is a convenient extension to “create, copy, store and upload screenshots”. To use it while drawing mode is active, toggle the area selection mode thanks to the Screenshot Tool shortcut (`Super + F11` by default, see its preferences) and **hold** the `space` key when selecting the area with pointer to avoid drawing.
+

draw.js

@@ -213,6 +213,9 @@ var DrawingArea = new Lang.Class({
     },
     
     _onButtonPressed: function(actor, event) {
+        if (this.spaceKeyPressed)
+            return Clutter.EVENT_PROPAGATE;
+        
         let button = event.get_button();
         let [x, y] = event.get_coords();
         let shiftPressed = event.has_shift_modifier();
@@ -250,6 +253,20 @@ var DrawingArea = new Lang.Class({
         return Clutter.EVENT_STOP;
     },
     
+    _onStageKeyPressed: function(actor, event) {
+        if (event.get_key_symbol() == Clutter.KEY_space)
+            this.spaceKeyPressed = true;
+        
+        return Clutter.EVENT_PROPAGATE;
+    },
+    
+    _onStageKeyReleased: function(actor, event) {
+        if (event.get_key_symbol() == Clutter.KEY_space)
+            this.spaceKeyPressed = false;
+        
+        return Clutter.EVENT_PROPAGATE;
+    },
+    
     _onKeyPressed: function(actor, event) {
         if (event.get_key_symbol() == Clutter.Escape) {
             this.emit('stop-drawing');
@@ -332,6 +349,9 @@ var DrawingArea = new Lang.Class({
         }
         
         this.motionHandler = this.connect('motion-event', (actor, event) => {
+            if (this.spaceKeyPressed)
+                return;
+            
             let coords = event.get_coords();
             let [s, x, y] = this.transform_stage_point(coords[0], coords[1]);
             if (!s)
@@ -579,6 +599,8 @@ var DrawingArea = new Lang.Class({
     },
     
     enterDrawingMode: function() {
+        this.stageKeyPressedHandler = global.stage.connect('key-press-event', this._onStageKeyPressed.bind(this));
+        this.stageKeyReleasedHandler = global.stage.connect('key-release-event', this._onStageKeyReleased.bind(this));
         this.keyPressedHandler = this.connect('key-press-event', this._onKeyPressed.bind(this));
         this.buttonPressedHandler = this.connect('button-press-event', this._onButtonPressed.bind(this));
         this._onKeyboardPopupMenuHandler = this.connect('popup-menu', this._onKeyboardPopupMenu.bind(this));
@@ -588,6 +610,14 @@ var DrawingArea = new Lang.Class({
     },
     
     leaveDrawingMode: function(save) {
+        if (this.stageKeyPressedHandler) {
+            global.stage.disconnect(this.stageKeyPressedHandler);
+            this.stageKeyPressedHandler = null;
+        }
+        if (this.stageKeyReleasedHandler) {
+            global.stage.disconnect(this.stageKeyReleasedHandler);
+            this.stageKeyReleasedHandler = null;
+        }
         if (this.keyPressedHandler) {
             this.disconnect(this.keyPressedHandler);
             this.keyPressedHandler = null;

locale/draw-on-your-screen.pot

@@ -262,6 +262,12 @@ msgstr ""
 msgid "Shift key held"
 msgstr ""
 
+msgid "Ignore pointer movement"
+msgstr ""
+
+msgid "Space key held"
+msgstr ""
+
 msgid "Leave"
 msgstr ""
 

prefs.js

@@ -83,6 +83,7 @@ var OTHER_SHORTCUTS = [
     { desc: "Increment/decrement line width", shortcut: "Scroll" },
     { desc: "Select color", shortcut: "Ctrl+1...9" },
     { desc: "Select eraser", shortcut: "Shift key held" },
+    { desc: "Ignore pointer movement", shortcut: "Space key held" },
     { desc: "Leave", shortcut: "Escape key" }
 ];