detect touch shape on iphone or android?

Question

Is there a public or private API that would let application get the surface that was touched? I am interested in Android and/or iOS.

In other words, I am intrested in shape of the finger that touched the screen.

A solution that would return a matrix of touched rectangles would be ok too.

(I am 90% positive there is no such thing, but I hope someone can prove me wrong)

I do not know of anything like that on iOS. iOS detects where your fingers are itself, I don't think you can get access to the raw sensor information. — fishinear, Jan 08 '12 at 19:14
Unless someone has found a way, I don't think this is available on Android. Android registers touches in single pixel coordinates and I'd think you'd have to bypass the OS and get to the hardware level. — DeeV, Jan 23 '12 at 18:12
On Android, I should think that the best you can do is use the MotionEvent.getSize(), which returns the size of the finger (not the shape though). http://developer.android.com/reference/android/view/MotionEvent.html#getSize%28int%29 — Jave, Jan 24 '12 at 09:01
@Deev, fishinear: it is possible on both platforms, see my answer... but I would still like to find some other method, hack, additional info under what conditions can be done... I will give bounty to anyone who provides the most additional information. — johndodo, Jan 26 '12 at 12:26

score 3 · Accepted Answer · answered Jan 26 '12 at 12:34

3

Answer as per request:
On Android, I should think that the best you can do is use the MotionEvent.getSize(), which returns the size of the finger (not the shape though). The API demo TouchPaint uses this.

answered Jan 26 '12 at 12:34

Jave

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Thanks for the help, Jave! I have posted a whole solution (iPhone too) in a separate answer below. – johndodo Jan 30 '12 at 08:18

score 1 · Answer 2 · answered Jan 24 '12 at 00:41

1

This code is an idea about how to get the touched rectangles. For each new rectangle touched a counter will be added 1, so there is easier track the touch movement (if needed). For more accuracy, change the values for the constants ROWS and COLS

#define ROWS 15
#define COLS ROWS

int matrix[ROWS][COLS];
int squareCounter;


- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [[event allTouches] anyObject];
    CGPoint location = [touch locationInView:touch.view];

    int col = floor((location.x * COLS) / self.view.frame.size.width);
    int row = floor((location.y * ROWS) / self.view.frame.size.height);
    if (matrix[col][row] == 0) matrix [col][row] = ++ squareCounter;

    [label setText:[NSString stringWithFormat:@"[%d][%d] -> %d", col, row, matrix[col][row]]];
}

- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    NSString *matrixStr = @"";
    for (int i = 0; i < COLS; i++) {
        for (int j = 0; j < ROWS; j++) {
            matrixStr = [matrixStr stringByAppendingFormat:@"%d\t", matrix[j][i]];
        }
        matrixStr = [matrixStr stringByAppendingString:@"\n"];
    }

    NSLog(@"Matrix:\n%@", matrixStr);
}

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    squareCounter = 0;
    for (int i = 0; i < ROWS; i++) {
        for (int j = 0; j < COLS; j++) {
            matrix[i][j] = 0;
        }
    }
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

It must be placed on the view controller whose view you want to detect the touch shape.

answered Jan 24 '12 at 00:41

Esepakuto

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If I understand correctly, only the center of the touch is reported by iOS? So this code follows the center of the finger and saves its path (and not shape) in matrix? – johndodo Jan 24 '12 at 06:47
That's it. In iOS the touch recognizers send only an X and an Y by touch. If you want to track two fingers the only that you have to do is to have a matrix by finger and relation between that matrix and the touch – Esepakuto Jan 24 '12 at 08:38
Ok, so if I want the shape of a **single** finger when **not** moving around, I am out of luck? BTW, even the size of area covered by finger would help... Android seems to support this (see my answer), how about iOS? – johndodo Jan 24 '12 at 09:00
I think that's a problen related with screen thechnology. The resistive screen can give something like the matrix of points pressed. But capacitive screens works in other way, I seriously doubt that you can get the aproximate shape because of the big number of points you need to define the shape. – Esepakuto Jan 24 '12 at 10:21
Approximate size of touch area would be enough for me - is this possible on iOS? Note that Android seems to support this, so I guess it should be possible (hardware-wise). – johndodo Jan 24 '12 at 10:25
I gess Android suports it because of the resistive screen devices. Did you get it work on a capacitive device? – Esepakuto Jan 24 '12 at 10:29
Actually, even iPhone **does** support this - I have updated my own answer. We are just not *allowed* to use it. :( – johndodo Jan 24 '12 at 10:59

score 1 · Answer 3 · edited May 23 '17 at 12:11

I have found the solution for Android: https://stackoverflow.com/questions/8977510/motionevent-pointercoords-gettouchmajor-device-support. I still need to find out how supported it is though...

And for iPhone: Is there any way at all that I can tell how hard the screen is being pressed (see accepted answer). It seems there is no official way, however.

Still, I would appreciate if someone added some official or unofficial / hackish methods.

detect touch shape on iphone or android?

3 Answers3