[main]: Add mdp to lecture notes
This commit is contained in:
70 files changed
+2759
No files matched your search
@@ -0,0 +1,192 @@
|
||||
# Touch Technology
|
||||
|
||||
#### Resistive Touch Screen
|
||||
|
||||
- Two sheets of transparent layers with metallic (resistive) coating facing each other with a thin gap in between
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
- Can be used with a finger or any pointing device (passive)
|
||||
- Requires a certain amount of pressure (to get the resistance to register)
|
||||
- Can be modified for multi-touch (only two touches)
|
||||
- Has high tolerance for liquids and contaminants
|
||||
- They're still used in hospitals and industry where fluids have a high spill rate
|
||||
|
||||
#### Surface Capacitive Touch Screen
|
||||
|
||||
- Screen is covered in a capacitive material
|
||||
- This is 90% transparent
|
||||
- Capacitance - ability to store electrical charge (this works through glass)
|
||||
- We apply a small voltage to generate an electrostatic field
|
||||
- Humans naturally act as small capacitors; touching the screen with a finger creates a dynamic capacitor.
|
||||
- Measure the effective capacitance at each corner of the screen
|
||||
- The larger the change, the closer to the corner the touch was
|
||||
- Combine these measurements from all corners to find the exact location of the touch
|
||||
|
||||
|
||||
|
||||
Using the distance from all 4 corners to determine the location. This only actually needs 3 corners; the 4th is used for accuracy.
|
||||
|
||||
##### Projected (Mutual) Capacitance
|
||||
|
||||
For multi-touch, there is a grid of sensors.
|
||||
|
||||
|
||||
|
||||
- Conductive material is etched with rows & columns
|
||||
- An electric field is projected through the top layer of the glass
|
||||
- A human acts as a conductor; a decrease in capacitance between electrodes is detected as a touch
|
||||
|
||||
The 1st-generation iPhone had a 10 x 15 (150) grid of sensors.
|
||||
|
||||
To get a higher resolution:
|
||||
|
||||
|
||||
|
||||
Similarly, we can do this with multiple touches
|
||||
|
||||
|
||||
|
||||
#### 3D touch
|
||||
|
||||
- Pressure-sensitive touch
|
||||
- This involves flexible glass
|
||||
- Pressing forces the finger closer to the rear capacitor
|
||||
- We can use this to measure depth, not location
|
||||
|
||||
# Gestures
|
||||
|
||||
Gesture - A series of touch events that occur over a period of time
|
||||
|
||||
`TouchBegin()`, `TouchMoved()`, `TouchEnded()`
|
||||
|
||||
Two ways to register these:
|
||||
|
||||
1. Implement `onTouchEvent()` in an activity
|
||||
2. Register a new `OnTouchListener` with a view - `setOnTouchListener(...)`
|
||||
|
||||
One or more fingers on the screen will trigger the callbacks of `onTouchEvent()` on the view.
|
||||
|
||||
Either way, the detailed interactions are delivered using a `MotionEvents` object
|
||||
|
||||
#### MotionEvent
|
||||
|
||||
This object encapsulates information about:
|
||||
|
||||
- Touch events
|
||||
- A touch begins (`ACTION_DOWN`)
|
||||
- The finger moves (`ACTION_MOVE`)
|
||||
- The touch ends (`ACTION_UP`)
|
||||
- (x,y) coordinates of the touch, information about pressure, size, orientation, etc.
|
||||
- Additional information for multi-touch, e.g. pointer ID, action index, etc.
|
||||
|
||||
###### ACTION_DOWN
|
||||
|
||||
- A gesture starts when a finger is pressed
|
||||
- A `MotionEvent` is generated for this
|
||||
- Find the action by calling `getAction()`
|
||||
- This can also have the identifier of the *pointer*, so use `getActionMasked()` for multi-touch
|
||||
|
||||
###### ACTION_MOVE
|
||||
|
||||
- As the finger moves, a series of ACTION_MOVE events will be sent
|
||||
- Find the new position using `getX()` and `getY()` (returns floats)
|
||||
- Note that Android bundles these into a series of touch events, so we can get historic touches
|
||||
|
||||
###### ACTION_UP
|
||||
|
||||
- A gesture ends in three ways
|
||||
1. `ACTION_UP` - last finger has been taken off the display
|
||||
2. `ACTION_CANCEL` event - another event happens, cancelling the gesture, e.g. the phone rings
|
||||
3. `ACTION_OUTSIDE` event - if the finger moves outside the relevant view
|
||||
|
||||
### Single Touch Gesture
|
||||
|
||||
Formed of:
|
||||
|
||||
1. A single `ACTION_DOWN`
|
||||
2. Zero or more `ACTION_MOVE`
|
||||
3. An `ACTION_UP` to finish
|
||||
|
||||
#### Single-touch interactions
|
||||
|
||||
- Positions are tracked to move an object
|
||||
- Use movement velocity for a swipe / fling
|
||||
|
||||
#### Dragging & Scrolling
|
||||
|
||||
- Store the original (x,y) touch location from ACTION_DOWN
|
||||
- Calculate changes from stored value and value returned from `ACTION_MOVE` or `ACTION_UP`
|
||||
- Adding the coordinate changes to the original object location
|
||||
|
||||
#### Swipe / Fling
|
||||
|
||||
- Rather than moving the object, we can calculate the velocity and direction
|
||||
- On `ACTION_UP`, continue to move the object with that velocity
|
||||
- Gives the user obvious visual feedback of *flinging* UI elements across the screen
|
||||
|
||||
#### Customised Gestures
|
||||
|
||||
Several different ways of tracking the movement of a gesture
|
||||
|
||||
- Use the starting and ending point of a pointer
|
||||
- Use the direction the pointer is travelling
|
||||
- Use velocity of the pointer
|
||||
- Use `getHistorical<Value>` to get historical movements
|
||||
|
||||
### Multi-touch Gestures
|
||||
|
||||
- Very similar to single touch
|
||||
- Same sequence of events with a few more events
|
||||
- `ACTION_POINTER_DOWN` & `ACTION_POINTER_UP`
|
||||
- Support for 256 touches at the same time
|
||||
|
||||
##### Determining Finger
|
||||
|
||||
- **Index**: position within the array in a `MotionEvent`
|
||||
- **ID**: Unique for each pointer (finger) to allow tracking an individual pointer across the entire gesture
|
||||
- The number of pointers can change as fingers are lifted or placed; so do the indices of the pointers
|
||||
- Each pointer is given an ID that won’t change
|
||||
- Need to track both the ID and past locations of pointers to move things about
|
||||
|
||||
|
||||
|
||||
`onTouchEvent` and `motionEvent`
|
||||
|
||||
- `onTouchEvent` is a callback method
|
||||
- `motionEvent` is an object that contains gesture information
|
||||
- When a user places fingers on the screen, it triggers the callback `onTouchEvent()` on the view
|
||||
- After some touch actions, the `motionEvent` delivered to `onTouchEvent()` provides the details of every interaction
|
||||
|
||||
```java
|
||||
public boolean onTouchEvent(MotionEvent event) {
|
||||
...
|
||||
int maskedAction = event.getActionMasked();
|
||||
switch (maskedAction) {
|
||||
case MotionEvent.ACTION_DOWN:
|
||||
case MotionEvent.ACTION_POINTER_DOWN:
|
||||
case MotionEvent.ACTION_MOVE:
|
||||
case MotionEvent.ACTION_UP:
|
||||
case MotionEvent.ACTION_POINTER_UP:
|
||||
case MotionEvent.ACTION_CANCEL:
|
||||
}
|
||||
```
|
||||
|
||||
#### Pinch to zoom
|
||||
|
||||
- Obtain the IDs of the two pointers
|
||||
- Use this to get the index so we can get locations
|
||||
- Calculate and store the distance between the two pointers
|
||||
- The ratio of the new distance to the old one gives the zoom / scale ratio
|
||||
|
||||
#### Two-finger rotation
|
||||
|
||||
- Obtain the IDs of the two pointers
|
||||
- Use this to get the index so we can get locations
|
||||
- Use the vertical and horizontal location difference to calculate the initial angle
|
||||
- Obtain the new locations of the two pointers to derive the new angle
|
||||
- Object can be rotated using the difference in angles
|
||||
Reference in new issue
Block a user