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1 /*
2  * Copyright (C) 2006-2009 Google Inc. All rights reserved.
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions are
6  * met:
7  *
8  *     * Redistributions of source code must retain the above copyright
9  * notice, this list of conditions and the following disclaimer.
10  *     * Redistributions in binary form must reproduce the above
11  * copyright notice, this list of conditions and the following disclaimer
12  * in the documentation and/or other materials provided with the
13  * distribution.
14  *     * Neither the name of Google Inc. nor the names of its
15  * contributors may be used to endorse or promote products derived from
16  * this software without specific prior written permission.
17  *
18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29  */
30 
31 #include "config.h"
32 #include "WebInputEventFactory.h"
33 
34 #include "KeyboardCodes.h"
35 #include "KeyCodeConversion.h"
36 
37 #include "WebInputEvent.h"
38 
39 #include <gdk/gdk.h>
40 #include <gdk/gdkkeysyms.h>
41 #include <gtk/gtk.h>
42 #include <gtk/gtkversion.h>
43 
44 #include <wtf/Assertions.h>
45 
46 namespace {
47 
48 // For click count tracking.
49 static int gNumClicks = 0;
50 static GdkWindow* gLastClickEventWindow = 0;
51 static gint gLastClickTime = 0;
52 static gint gLastClickX = 0;
53 static gint gLastClickY = 0;
54 static WebKit::WebMouseEvent::Button gLastClickButton = WebKit::WebMouseEvent::ButtonNone;
55 
shouldForgetPreviousClick(GdkWindow * window,gint time,gint x,gint y)56 bool shouldForgetPreviousClick(GdkWindow* window, gint time, gint x, gint y)
57 {
58     static GtkSettings* settings = gtk_settings_get_default();
59 
60     if (window != gLastClickEventWindow)
61       return true;
62 
63     gint doubleClickTime = 250;
64     gint doubleClickDistance = 5;
65     g_object_get(G_OBJECT(settings),
66                  "gtk-double-click-time", &doubleClickTime,
67                  "gtk-double-click-distance", &doubleClickDistance, NULL);
68     return (time - gLastClickTime) > doubleClickTime
69            || abs(x - gLastClickX) > doubleClickDistance
70            || abs(y - gLastClickY) > doubleClickDistance;
71 }
72 
resetClickCountState()73 void resetClickCountState()
74 {
75     gNumClicks = 0;
76     gLastClickEventWindow = 0;
77     gLastClickTime = 0;
78     gLastClickX = 0;
79     gLastClickY = 0;
80     gLastClickButton = WebKit::WebMouseEvent::ButtonNone;
81 }
82 
83 }  // namespace
84 
85 namespace WebKit {
86 
gdkEventTimeToWebEventTime(guint32 time)87 static double gdkEventTimeToWebEventTime(guint32 time)
88 {
89     // Convert from time in ms to time in sec.
90     return time / 1000.0;
91 }
92 
gdkStateToWebEventModifiers(guint state)93 static int gdkStateToWebEventModifiers(guint state)
94 {
95     int modifiers = 0;
96     if (state & GDK_SHIFT_MASK)
97         modifiers |= WebInputEvent::ShiftKey;
98     if (state & GDK_CONTROL_MASK)
99         modifiers |= WebInputEvent::ControlKey;
100     if (state & GDK_MOD1_MASK)
101         modifiers |= WebInputEvent::AltKey;
102 #if GTK_CHECK_VERSION(2, 10, 0)
103     if (state & GDK_META_MASK)
104         modifiers |= WebInputEvent::MetaKey;
105 #endif
106     if (state & GDK_BUTTON1_MASK)
107         modifiers |= WebInputEvent::LeftButtonDown;
108     if (state & GDK_BUTTON2_MASK)
109         modifiers |= WebInputEvent::MiddleButtonDown;
110     if (state & GDK_BUTTON3_MASK)
111         modifiers |= WebInputEvent::RightButtonDown;
112     if (state & GDK_LOCK_MASK)
113         modifiers |= WebInputEvent::CapsLockOn;
114     if (state & GDK_MOD2_MASK)
115         modifiers |= WebInputEvent::NumLockOn;
116     return modifiers;
117 }
118 
gdkEventToWindowsKeyCode(const GdkEventKey * event)119 static int gdkEventToWindowsKeyCode(const GdkEventKey* event)
120 {
121     static const unsigned int hardwareCodeToGDKKeyval[] = {
122         0,                 // 0x00:
123         0,                 // 0x01:
124         0,                 // 0x02:
125         0,                 // 0x03:
126         0,                 // 0x04:
127         0,                 // 0x05:
128         0,                 // 0x06:
129         0,                 // 0x07:
130         0,                 // 0x08:
131         0,                 // 0x09: GDK_Escape
132         GDK_1,             // 0x0A: GDK_1
133         GDK_2,             // 0x0B: GDK_2
134         GDK_3,             // 0x0C: GDK_3
135         GDK_4,             // 0x0D: GDK_4
136         GDK_5,             // 0x0E: GDK_5
137         GDK_6,             // 0x0F: GDK_6
138         GDK_7,             // 0x10: GDK_7
139         GDK_8,             // 0x11: GDK_8
140         GDK_9,             // 0x12: GDK_9
141         GDK_0,             // 0x13: GDK_0
142         GDK_minus,         // 0x14: GDK_minus
143         GDK_equal,         // 0x15: GDK_equal
144         0,                 // 0x16: GDK_BackSpace
145         0,                 // 0x17: GDK_Tab
146         GDK_q,             // 0x18: GDK_q
147         GDK_w,             // 0x19: GDK_w
148         GDK_e,             // 0x1A: GDK_e
149         GDK_r,             // 0x1B: GDK_r
150         GDK_t,             // 0x1C: GDK_t
151         GDK_y,             // 0x1D: GDK_y
152         GDK_u,             // 0x1E: GDK_u
153         GDK_i,             // 0x1F: GDK_i
154         GDK_o,             // 0x20: GDK_o
155         GDK_p,             // 0x21: GDK_p
156         GDK_bracketleft,   // 0x22: GDK_bracketleft
157         GDK_bracketright,  // 0x23: GDK_bracketright
158         0,                 // 0x24: GDK_Return
159         0,                 // 0x25: GDK_Control_L
160         GDK_a,             // 0x26: GDK_a
161         GDK_s,             // 0x27: GDK_s
162         GDK_d,             // 0x28: GDK_d
163         GDK_f,             // 0x29: GDK_f
164         GDK_g,             // 0x2A: GDK_g
165         GDK_h,             // 0x2B: GDK_h
166         GDK_j,             // 0x2C: GDK_j
167         GDK_k,             // 0x2D: GDK_k
168         GDK_l,             // 0x2E: GDK_l
169         GDK_semicolon,     // 0x2F: GDK_semicolon
170         GDK_apostrophe,    // 0x30: GDK_apostrophe
171         GDK_grave,         // 0x31: GDK_grave
172         0,                 // 0x32: GDK_Shift_L
173         GDK_backslash,     // 0x33: GDK_backslash
174         GDK_z,             // 0x34: GDK_z
175         GDK_x,             // 0x35: GDK_x
176         GDK_c,             // 0x36: GDK_c
177         GDK_v,             // 0x37: GDK_v
178         GDK_b,             // 0x38: GDK_b
179         GDK_n,             // 0x39: GDK_n
180         GDK_m,             // 0x3A: GDK_m
181         GDK_comma,         // 0x3B: GDK_comma
182         GDK_period,        // 0x3C: GDK_period
183         GDK_slash,         // 0x3D: GDK_slash
184         0,                 // 0x3E: GDK_Shift_R
185         0,                 // 0x3F:
186         0,                 // 0x40:
187         0,                 // 0x41:
188         0,                 // 0x42:
189         0,                 // 0x43:
190         0,                 // 0x44:
191         0,                 // 0x45:
192         0,                 // 0x46:
193         0,                 // 0x47:
194         0,                 // 0x48:
195         0,                 // 0x49:
196         0,                 // 0x4A:
197         0,                 // 0x4B:
198         0,                 // 0x4C:
199         0,                 // 0x4D:
200         0,                 // 0x4E:
201         0,                 // 0x4F:
202         0,                 // 0x50:
203         0,                 // 0x51:
204         0,                 // 0x52:
205         0,                 // 0x53:
206         0,                 // 0x54:
207         0,                 // 0x55:
208         0,                 // 0x56:
209         0,                 // 0x57:
210         0,                 // 0x58:
211         0,                 // 0x59:
212         0,                 // 0x5A:
213         0,                 // 0x5B:
214         0,                 // 0x5C:
215         0,                 // 0x5D:
216         0,                 // 0x5E:
217         0,                 // 0x5F:
218         0,                 // 0x60:
219         0,                 // 0x61:
220         0,                 // 0x62:
221         0,                 // 0x63:
222         0,                 // 0x64:
223         0,                 // 0x65:
224         0,                 // 0x66:
225         0,                 // 0x67:
226         0,                 // 0x68:
227         0,                 // 0x69:
228         0,                 // 0x6A:
229         0,                 // 0x6B:
230         0,                 // 0x6C:
231         0,                 // 0x6D:
232         0,                 // 0x6E:
233         0,                 // 0x6F:
234         0,                 // 0x70:
235         0,                 // 0x71:
236         0,                 // 0x72:
237         GDK_Super_L,       // 0x73: GDK_Super_L
238         GDK_Super_R,       // 0x74: GDK_Super_R
239     };
240 
241     // |windowsKeyCode| has to include a valid virtual-key code even when we
242     // use non-US layouts, e.g. even when we type an 'A' key of a US keyboard
243     // on the Hebrew layout, |windowsKeyCode| should be VK_A.
244     // On the other hand, |event->keyval| value depends on the current
245     // GdkKeymap object, i.e. when we type an 'A' key of a US keyboard on
246     // the Hebrew layout, |event->keyval| becomes GDK_hebrew_shin and this
247     // WebCore::windowsKeyCodeForKeyEvent() call returns 0.
248     // To improve compatibilty with Windows, we use |event->hardware_keycode|
249     // for retrieving its Windows key-code for the keys when the
250     // WebCore::windowsKeyCodeForEvent() call returns 0.
251     // We shouldn't use |event->hardware_keycode| for keys that GdkKeymap
252     // objects cannot change because |event->hardware_keycode| doesn't change
253     // even when we change the layout options, e.g. when we swap a control
254     // key and a caps-lock key, GTK doesn't swap their
255     // |event->hardware_keycode| values but swap their |event->keyval| values.
256     int windowsKeyCode = WebCore::windowsKeyCodeForKeyEvent(event->keyval);
257     if (windowsKeyCode)
258         return windowsKeyCode;
259 
260     const int tableSize = sizeof(hardwareCodeToGDKKeyval) / sizeof(hardwareCodeToGDKKeyval[0]);
261     if (event->hardware_keycode < tableSize) {
262         int keyval = hardwareCodeToGDKKeyval[event->hardware_keycode];
263         if (keyval)
264             return WebCore::windowsKeyCodeForKeyEvent(keyval);
265     }
266 
267     // This key is one that keyboard-layout drivers cannot change.
268     // Use |event->keyval| to retrieve its |windowsKeyCode| value.
269     return WebCore::windowsKeyCodeForKeyEvent(event->keyval);
270 }
271 
272 // Gets the corresponding control character of a specified key code. See:
273 // http://en.wikipedia.org/wiki/Control_characters
274 // We emulate Windows behavior here.
getControlCharacter(int windowsKeyCode,bool shift)275 static WebUChar getControlCharacter(int windowsKeyCode, bool shift)
276 {
277     if (windowsKeyCode >= WebCore::VKEY_A && windowsKeyCode <= WebCore::VKEY_Z) {
278         // ctrl-A ~ ctrl-Z map to \x01 ~ \x1A
279         return windowsKeyCode - WebCore::VKEY_A + 1;
280     }
281     if (shift) {
282         // following graphics chars require shift key to input.
283         switch (windowsKeyCode) {
284         // ctrl-@ maps to \x00 (Null byte)
285         case WebCore::VKEY_2:
286             return 0;
287         // ctrl-^ maps to \x1E (Record separator, Information separator two)
288         case WebCore::VKEY_6:
289             return 0x1E;
290         // ctrl-_ maps to \x1F (Unit separator, Information separator one)
291         case WebCore::VKEY_OEM_MINUS:
292             return 0x1F;
293         // Returns 0 for all other keys to avoid inputting unexpected chars.
294         default:
295             return 0;
296         }
297     } else {
298         switch (windowsKeyCode) {
299         // ctrl-[ maps to \x1B (Escape)
300         case WebCore::VKEY_OEM_4:
301             return 0x1B;
302         // ctrl-\ maps to \x1C (File separator, Information separator four)
303         case WebCore::VKEY_OEM_5:
304             return 0x1C;
305         // ctrl-] maps to \x1D (Group separator, Information separator three)
306         case WebCore::VKEY_OEM_6:
307             return 0x1D;
308         // ctrl-Enter maps to \x0A (Line feed)
309         case WebCore::VKEY_RETURN:
310             return 0x0A;
311         // Returns 0 for all other keys to avoid inputting unexpected chars.
312         default:
313             return 0;
314         }
315     }
316 }
317 
318 // WebKeyboardEvent -----------------------------------------------------------
319 
keyboardEvent(const GdkEventKey * event)320 WebKeyboardEvent WebInputEventFactory::keyboardEvent(const GdkEventKey* event)
321 {
322     WebKeyboardEvent result;
323 
324     result.timeStampSeconds = gdkEventTimeToWebEventTime(event->time);
325     result.modifiers = gdkStateToWebEventModifiers(event->state);
326 
327     switch (event->type) {
328     case GDK_KEY_RELEASE:
329         result.type = WebInputEvent::KeyUp;
330         break;
331     case GDK_KEY_PRESS:
332         result.type = WebInputEvent::RawKeyDown;
333         break;
334     default:
335         ASSERT_NOT_REACHED();
336     }
337 
338     // According to MSDN:
339     // http://msdn.microsoft.com/en-us/library/ms646286(VS.85).aspx
340     // Key events with Alt modifier and F10 are system key events.
341     // We just emulate this behavior. It's necessary to prevent webkit from
342     // processing keypress event generated by alt-d, etc.
343     // F10 is not special on Linux, so don't treat it as system key.
344     if (result.modifiers & WebInputEvent::AltKey)
345         result.isSystemKey = true;
346 
347     // The key code tells us which physical key was pressed (for example, the
348     // A key went down or up).  It does not determine whether A should be lower
349     // or upper case.  This is what text does, which should be the keyval.
350     result.windowsKeyCode = gdkEventToWindowsKeyCode(event);
351     result.nativeKeyCode = event->hardware_keycode;
352 
353     if (result.windowsKeyCode == WebCore::VKEY_RETURN)
354         // We need to treat the enter key as a key press of character \r.  This
355         // is apparently just how webkit handles it and what it expects.
356         result.unmodifiedText[0] = '\r';
357     else
358         // FIXME: fix for non BMP chars
359         result.unmodifiedText[0] =
360             static_cast<WebUChar>(gdk_keyval_to_unicode(event->keyval));
361 
362     // If ctrl key is pressed down, then control character shall be input.
363     if (result.modifiers & WebInputEvent::ControlKey)
364         result.text[0] = getControlCharacter(
365             result.windowsKeyCode, result.modifiers & WebInputEvent::ShiftKey);
366     else
367         result.text[0] = result.unmodifiedText[0];
368 
369     result.setKeyIdentifierFromWindowsKeyCode();
370 
371     // FIXME: Do we need to set IsAutoRepeat or IsKeyPad?
372 
373     return result;
374 }
375 
keyboardEvent(wchar_t character,int state,double timeStampSeconds)376 WebKeyboardEvent WebInputEventFactory::keyboardEvent(wchar_t character, int state, double timeStampSeconds)
377 {
378     // keyboardEvent(const GdkEventKey*) depends on the GdkEventKey object and
379     // it is hard to use/ it from signal handlers which don't use GdkEventKey
380     // objects (e.g. GtkIMContext signal handlers.) For such handlers, this
381     // function creates a WebInputEvent::Char event without using a
382     // GdkEventKey object.
383     WebKeyboardEvent result;
384     result.type = WebKit::WebInputEvent::Char;
385     result.timeStampSeconds = timeStampSeconds;
386     result.modifiers = gdkStateToWebEventModifiers(state);
387     result.windowsKeyCode = character;
388     result.nativeKeyCode = character;
389     result.text[0] = character;
390     result.unmodifiedText[0] = character;
391 
392     // According to MSDN:
393     // http://msdn.microsoft.com/en-us/library/ms646286(VS.85).aspx
394     // Key events with Alt modifier and F10 are system key events.
395     // We just emulate this behavior. It's necessary to prevent webkit from
396     // processing keypress event generated by alt-d, etc.
397     // F10 is not special on Linux, so don't treat it as system key.
398     if (result.modifiers & WebInputEvent::AltKey)
399         result.isSystemKey = true;
400 
401     return result;
402 }
403 
404 // WebMouseEvent --------------------------------------------------------------
405 
mouseEvent(const GdkEventButton * event)406 WebMouseEvent WebInputEventFactory::mouseEvent(const GdkEventButton* event)
407 {
408     WebMouseEvent result;
409 
410     result.timeStampSeconds = gdkEventTimeToWebEventTime(event->time);
411 
412     result.modifiers = gdkStateToWebEventModifiers(event->state);
413     result.x = static_cast<int>(event->x);
414     result.y = static_cast<int>(event->y);
415     result.windowX = result.x;
416     result.windowY = result.y;
417     result.globalX = static_cast<int>(event->x_root);
418     result.globalY = static_cast<int>(event->y_root);
419     result.clickCount = 0;
420 
421     switch (event->type) {
422     case GDK_BUTTON_PRESS:
423         result.type = WebInputEvent::MouseDown;
424         break;
425     case GDK_BUTTON_RELEASE:
426         result.type = WebInputEvent::MouseUp;
427         break;
428     case GDK_3BUTTON_PRESS:
429     case GDK_2BUTTON_PRESS:
430     default:
431         ASSERT_NOT_REACHED();
432     };
433 
434     result.button = WebMouseEvent::ButtonNone;
435     if (event->button == 1)
436         result.button = WebMouseEvent::ButtonLeft;
437     else if (event->button == 2)
438         result.button = WebMouseEvent::ButtonMiddle;
439     else if (event->button == 3)
440         result.button = WebMouseEvent::ButtonRight;
441 
442     if (result.type == WebInputEvent::MouseDown) {
443         bool forgetPreviousClick = shouldForgetPreviousClick(event->window, event->time, event->x, event->y);
444 
445         if (!forgetPreviousClick && result.button == gLastClickButton)
446             ++gNumClicks;
447         else {
448             gNumClicks = 1;
449 
450             gLastClickEventWindow = event->window;
451             gLastClickX = event->x;
452             gLastClickY = event->y;
453             gLastClickButton = result.button;
454         }
455         gLastClickTime = event->time;
456     }
457     result.clickCount = gNumClicks;
458 
459     return result;
460 }
461 
mouseEvent(const GdkEventMotion * event)462 WebMouseEvent WebInputEventFactory::mouseEvent(const GdkEventMotion* event)
463 {
464     WebMouseEvent result;
465 
466     result.timeStampSeconds = gdkEventTimeToWebEventTime(event->time);
467     result.modifiers = gdkStateToWebEventModifiers(event->state);
468     result.x = static_cast<int>(event->x);
469     result.y = static_cast<int>(event->y);
470     result.windowX = result.x;
471     result.windowY = result.y;
472     result.globalX = static_cast<int>(event->x_root);
473     result.globalY = static_cast<int>(event->y_root);
474 
475     switch (event->type) {
476     case GDK_MOTION_NOTIFY:
477         result.type = WebInputEvent::MouseMove;
478         break;
479     default:
480         ASSERT_NOT_REACHED();
481     }
482 
483     result.button = WebMouseEvent::ButtonNone;
484     if (event->state & GDK_BUTTON1_MASK)
485         result.button = WebMouseEvent::ButtonLeft;
486     else if (event->state & GDK_BUTTON2_MASK)
487         result.button = WebMouseEvent::ButtonMiddle;
488     else if (event->state & GDK_BUTTON3_MASK)
489         result.button = WebMouseEvent::ButtonRight;
490 
491     if (shouldForgetPreviousClick(event->window, event->time, event->x, event->y))
492         resetClickCountState();
493 
494     return result;
495 }
496 
mouseEvent(const GdkEventCrossing * event)497 WebMouseEvent WebInputEventFactory::mouseEvent(const GdkEventCrossing* event)
498 {
499     WebMouseEvent result;
500 
501     result.timeStampSeconds = gdkEventTimeToWebEventTime(event->time);
502     result.modifiers = gdkStateToWebEventModifiers(event->state);
503     result.x = static_cast<int>(event->x);
504     result.y = static_cast<int>(event->y);
505     result.windowX = result.x;
506     result.windowY = result.y;
507     result.globalX = static_cast<int>(event->x_root);
508     result.globalY = static_cast<int>(event->y_root);
509 
510     switch (event->type) {
511     case GDK_ENTER_NOTIFY:
512     case GDK_LEAVE_NOTIFY:
513         // Note that if we sent MouseEnter or MouseLeave to WebKit, it
514         // wouldn't work - they don't result in the proper JavaScript events.
515         // MouseMove does the right thing.
516         result.type = WebInputEvent::MouseMove;
517         break;
518     default:
519         ASSERT_NOT_REACHED();
520     }
521 
522     result.button = WebMouseEvent::ButtonNone;
523     if (event->state & GDK_BUTTON1_MASK)
524         result.button = WebMouseEvent::ButtonLeft;
525     else if (event->state & GDK_BUTTON2_MASK)
526         result.button = WebMouseEvent::ButtonMiddle;
527     else if (event->state & GDK_BUTTON3_MASK)
528         result.button = WebMouseEvent::ButtonRight;
529 
530     if (shouldForgetPreviousClick(event->window, event->time, event->x, event->y))
531         resetClickCountState();
532 
533     return result;
534 }
535 
536 // WebMouseWheelEvent ---------------------------------------------------------
537 
mouseWheelEvent(const GdkEventScroll * event)538 WebMouseWheelEvent WebInputEventFactory::mouseWheelEvent(const GdkEventScroll* event)
539 {
540     WebMouseWheelEvent result;
541 
542     result.type = WebInputEvent::MouseWheel;
543     result.button = WebMouseEvent::ButtonNone;
544 
545     result.timeStampSeconds = gdkEventTimeToWebEventTime(event->time);
546     result.modifiers = gdkStateToWebEventModifiers(event->state);
547     result.x = static_cast<int>(event->x);
548     result.y = static_cast<int>(event->y);
549     result.windowX = result.x;
550     result.windowY = result.y;
551     result.globalX = static_cast<int>(event->x_root);
552     result.globalY = static_cast<int>(event->y_root);
553 
554     // How much should we scroll per mouse wheel event?
555     // - Windows uses 3 lines by default and obeys a system setting.
556     // - Mozilla has a pref that lets you either use the "system" number of lines
557     //   to scroll, or lets the user override it.
558     //   For the "system" number of lines, it appears they've hardcoded 3.
559     //   See case NS_MOUSE_SCROLL in content/events/src/nsEventStateManager.cpp
560     //   and InitMouseScrollEvent in widget/src/gtk2/nsCommonWidget.cpp .
561     // - Gtk makes the scroll amount a function of the size of the scroll bar,
562     //   which is not available to us here.
563     // Instead, we pick a number that empirically matches Firefox's behavior.
564     static const float scrollbarPixelsPerTick = 160.0f / 3.0f;
565 
566     switch (event->direction) {
567     case GDK_SCROLL_UP:
568         result.deltaY = scrollbarPixelsPerTick;
569         result.wheelTicksY = 1;
570         break;
571     case GDK_SCROLL_DOWN:
572         result.deltaY = -scrollbarPixelsPerTick;
573         result.wheelTicksY = -1;
574         break;
575     case GDK_SCROLL_LEFT:
576         result.deltaX = scrollbarPixelsPerTick;
577         result.wheelTicksX = 1;
578         break;
579     case GDK_SCROLL_RIGHT:
580         result.deltaX = -scrollbarPixelsPerTick;
581         result.wheelTicksX = -1;
582         break;
583     }
584 
585     return result;
586 }
587 
588 } // namespace WebKit
589