|
Utilizing dragging and gesturesThis artice should describe the different possibilities of Disko to handle user input. It will focus on the abilities to process user input for dragging elements within a gui application. Input TypesDisko disko can handle input events from mulitiple sources like X11, DirectFB or the Linux input sybsytem. It distinguishes two fundamental types of inputs: Keyboard events (like keys on a keyboard or ther dedicated hardware buttons) and pointer events (mouse clicks, mouse movement or touchscreen events). Any input event will be one of:
The appropriate inputs are automatically seleceted implicitly by the desired backend system (Linux Framebuffer, X11, DirectFB). Handling InputsThe direct inputs from the hardware are normally handled by disko and its gui elements automatically (widget inputs, z-order changes, focus changes, etc). However if the interface needs to be a little smarter than the default beahaviour of disko there are some ways of controlling the inputs for the developer. Intercepting window inputsThe window input handling can be interfaced using one of emmited signals, that are emitted during the input event processing: MMSWindow::onHandleInput() MMSWindow::onBeforeHandleInput() Guessing user inputDisko provides a very way of guessing basic gestures. The class MMSInputGesture is provided for that purpose. It can collect Axismotion events, and the can taḱe a guess if and in which direction a swipe gesture took place. A sample window callback could look like this: bool beforeInputCB(MMSWindow *win, MMSInputEvent *event) {
static MMSInputGesture gest;
gest.addInfo(event);
MMSINPUTGESTURE guess = gest.guess();
switch(guess) {
case MMSINPUTGESTURE_UKN:
break;
case MMSINPUTGESTURE_UP:
case MMSINPUTGESTURE_DOWN:
//handle vertical swipe
handleVSwipe(guess);
//stop processing chain
return true;
case MMSINPUTGESTURE_LEFT:
case MMSINPUTGESTURE_RIGHT:
//handle horizontal swipe
handleHSwipe(guess);
//stop processing chain
return true;
}
//proceed normally
return false;
}
Identify dragging eventsTo identify a dragging event it is necessary to identify a sequence of input events: ButtonPress -> AxisMotion -> ButtonRelease. A Simple dragging of a Window could be achieved easily: bool beforeInputCB(MMSWindow *win, MMSInputEvent *event) {
static bool drag=false;
if(event->type == MMSINPUTEVENTTYPE_BUTTONPRESS) {
drag=true;
//proceed normally
return false;
}
if(event->type == MMSINPUTEVENTTYPE_BUTTONRELEASE) {
drag=false;
//proceed normally
return false;
}
if(event->type == MMSINPUTEVENTTYPE_AXISMOTION) {
MMSFBRectangle rect=win->getGeometry();
win->moveTo(rect.x+event->dx, rect.y+event->dy);
//end event processing
return true;
}
//proceed normally
return false;
}
This example will simply change the window position according to the pointer movement that to place between the >press and release envents. In our latest version of the disko demos (LINK HIER!!!!!!!!!!) we utilize some additional mechanism to reduce spent cpu power and to create a more convenient user experience. Before an actual dragging operation is started, the axismotion dx or dy amounts must exceed a specific threshold. This ensures that slight slips in the handling (like when using an on screen keyboard) do trigger the dragging mode. Theres also a threshold that needs to be exceeded for redrawing the user interface during a draggin operation (e.g. every 10px). This leads to a much reduced cpu usage. MMSInputEvent in DetailThe MMSinputEvent provides several different informations. It contais the event type, a keysymbol if applicabe (keypress, keyrelease) and 3 sets of coordinates for different purposes:
|
Contents