MessageReceived(): Override B_MOUSE_WHEEL_CHANGED when in alternative screen

mode and send the key/page up/down escape sequences instead of trying to
scroll. Makes mouse wheel scrolling in less, nano,... working. Closes #6460.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@39589 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/apps/terminal/TermView.cpp

@@ -1937,6 +1937,54 @@ TermView::MessageReceived(BMessage *msg)
 			break;
 		}
 
+		case B_MOUSE_WHEEL_CHANGED:
+		{
+			// overridden to allow scrolling emulation in alternative screen
+			// mode
+			BAutolock locker(fTextBuffer);
+			float deltaY = 0;
+			if (fTextBuffer->IsAlternateScreenActive()
+				&& msg->FindFloat("be:wheel_delta_y", &deltaY) == B_OK
+				&& deltaY != 0) {
+				// We are in alternative screen mode and have a vertical delta
+				// we can work with -- emulate scrolling via terminal escape
+				// sequences.
+				locker.Unlock();
+
+				// scroll pagewise, if one of Option, Command, or Control is
+				// pressed
+				int32 steps;
+				const char* stepString;
+				if ((modifiers()
+						& (B_OPTION_KEY | B_COMMAND_KEY | B_CONTROL_KEY))
+						!= 0) {
+					// pagewise
+					stepString = deltaY > 0
+						? PAGE_DOWN_KEY_CODE : PAGE_UP_KEY_CODE;
+					steps = abs((int)deltaY);
+				} else {
+					// three lines per step
+					stepString = deltaY > 0
+						? DOWN_ARROW_KEY_CODE : UP_ARROW_KEY_CODE;
+					steps = 3 * abs((int)deltaY);
+				}
+
+				// We want to do only a single write(), so compose a string
+				// repeating the sequence as often as required by the delta.
+				BString toWrite;
+				for (int32 i = 0; i <steps; i++)
+					toWrite << stepString;
+
+				_WritePTY(toWrite.String(), toWrite.Length());
+			} else {
+				// let the BView's implementation handle the standard scrolling
+				locker.Unlock();
+				BView::MessageReceived(msg);
+			}
+
+			break;
+		}
+
 		case MENU_CLEAR_ALL:
 			Clear();
 			fShell->Write(ctrl_l, 1);