Resistive Touchscreen Calibration in Gingerbread [Patch]

[Gaurav Singh]

I have a resistive touchscreen with mechanical misalignments on my
board. The "5 point calibration method" solves errors caused by these
misalignments and converts Touchscreen controller data to actual
screen coordinates. A complete description of mechanical misalignments
and 5 point calibration method can be found at
http://focus.tij.co.jp/jp/lit/an/slyt277/slyt277.pdf.

5-point calibration method is part of the TSLIB touchscreen
calibration commonly used for our QT based devices. We can extend
Android's touchscreen Calibration parameters to include the 6
parameters that are part of the /etc/pointercal file ( calculated when
we run ts_calibrate on TSLIB). Sample idc file below:

# See output of /etc/pointercal file after running ts_calibrate on normal Linux
#
# Before running ts_calibrate -
# export TSLIB_TSDEVICE=/dev/input/event1
# export TSLIB_CALIBFILE=/etc/pointercal
# export TSLIB_CONFFILE=/etc/ts.conf
# export TSLIB_FBDEVICE=/dev/fb0
#
# Pointercal file format - xscale, xymix, xoffset, yxmix, yscale,
yoffset, divider.
# Enter here the values after dividing xscale etc. with the divider.
#

touch.5pointcalib.xscale = 0.199488
touch.5pointcalib.xymix = -0.000325
touch.5pointcalib.xoffset = -6.898865
touch.5pointcalib.yxmix = -0.000795
touch.5pointcalib.yscale = 0.124000
touch.5pointcalib.yoffset = -8.484802

I patched the Android Input subsystem to include the 5 point
calibration method for generating actual screen coordinates.
Gingerbread currently uses simple scaling of touchscreen X and Y data
to CLCD screen X and Y coordinates. In frameworks/base made the
following changes :

diff --git a/include/ui/InputReader.h b/include/ui/InputReader.h
index 49351b0..bb3ec5e 100644
--- a/include/ui/InputReader.h
+++ b/include/ui/InputReader.h
@@ -589,6 +589,20 @@ protected:

// Immutable calibration parameters in parsed form.
struct Calibration {
+ // 5 point calibration algorithm coefficients
+ bool havexscale;
+ float xscale;
+ bool havexymix;
+ float xymix;
+ bool havexoffset;
+ float xoffset;
+ bool haveyxmix;
+ float yxmix;
+ bool haveyscale;
+ float yscale;
+ bool haveyoffset;
+ float yoffset;
+
// Touch Size
enum TouchSizeCalibration {
TOUCH_SIZE_CALIBRATION_DEFAULT,
diff --git a/libs/ui/InputReader.cpp b/libs/ui/InputReader.cpp
index 3197ab2..9345dca 100644
--- a/libs/ui/InputReader.cpp
+++ b/libs/ui/InputReader.cpp
@@ -1682,6 +1682,20 @@ void TouchInputMapper::parseCalibration() {
const InputDeviceCalibration& in = getDevice()->getCalibration();
Calibration& out = mCalibration;

+ out.havexscale = in.tryGetProperty(String8("touch.5pointcalib.xscale"),
+ out.xscale);
+ out.havexymix = in.tryGetProperty(String8("touch.5pointcalib.xymix"),
+ out.xymix);
+ out.havexoffset = in.tryGetProperty(String8("touch.5pointcalib.xoffset"),
+ out.xoffset);
+ out.haveyxmix = in.tryGetProperty(String8("touch.5pointcalib.yxmix"),
+ out.yxmix);
+ out.haveyscale = in.tryGetProperty(String8("touch.5pointcalib.yscale"),
+ out.yscale);
+ out.haveyoffset = in.tryGetProperty(String8("touch.5pointcalib.yoffset"),
+ out.yoffset);
+
+
// Touch Size
out.touchSizeCalibration = Calibration::TOUCH_SIZE_CALIBRATION_DEFAULT;
String8 touchSizeCalibrationString;
@@ -2294,10 +2308,47 @@ void TouchInputMapper::dispatchTouch(nsecs_t
when, uint32_t policyFlags,
uint32_t inIndex = touch->idToIndex[id];

const PointerData& in = touch->pointers[inIndex];
+ float x,y;

// X and Y
- float x = float(in.x - mLocked.xOrigin) * mLocked.xScale;
- float y = float(in.y - mLocked.yOrigin) * mLocked.yScale;
+ if ( mCalibration.havexscale && mCalibration.havexymix &&
+ mCalibration.havexoffset && mCalibration.haveyxmix &&
+ mCalibration.haveyscale && mCalibration.haveyoffset) {
+
+ x = float(in.x - mLocked.xOrigin) * mLocked.xScale;
+ y = float(in.y - mLocked.yOrigin) * mLocked.yScale;
+ LOGI("x_orig = %f, y_orig = %f\n", x, y);
+ float x_temp = float(in.x - mLocked.xOrigin);
+ float y_temp = float(in.y - mLocked.yOrigin);
+
+ //float xscale = 0.199488;
+ //float xymix = -0.000325;
+ //float xoffset = -6.898865;
+ //float yxmix = -0.000795;
+ //float yscale = 0.124000;
+ //float yoffset = -8.484802;
+
+ // 5 point Calibration coefficients - from tsc.idc
+ float xscale = mCalibration.xscale;
+ float xymix = mCalibration.xymix;
+ float xoffset = mCalibration.xoffset;
+ float yxmix = mCalibration.yxmix;
+ float yscale = mCalibration.yscale;
+ float yoffset = mCalibration.yoffset;
+
+ float x_after_calib = (xscale * x_temp) + (xymix * y_temp) + xoffset;
+ float y_after_calib = (yxmix * x_temp) + (yscale * y_temp) + yoffset;
+
+
+ LOGI("x_after_calib = %f, y_after_calib = %f\n xscale = %f,
yoffset = %f\n", x_after_calib, y_after_calib, xscale, yoffset);
+ x = x_after_calib;
+ y = y_after_calib;
+
+ }
+ else {
+ x = float(in.x - mLocked.xOrigin) * mLocked.xScale;
+ y = float(in.y - mLocked.yOrigin) * mLocked.yScale;
+ }

// ToolMajor and ToolMinor
float toolMajor, toolMinor;

Touchscreen soft-keyboard inputs were being mis-reported on my WVGA
screen and with the patch, keypresses are more accurate.

Regards

[Ashwin Bihari]

Gaurav,

This is great, did you look into integrating TSLIB directly into
Android/Gingerbread instead of sucking in just the calibration values?

-- Ashwin

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>

[Gaurav Singh]

Hi Ashwin,

Instead of integrating TSLIB into Android you can use a simple Android
application that works like ts_calibrate (TSLIB test app) to get
calibration values.

Regards

[Ashwin Bihari]

Gaurav,

I know I can do that, but with Eclair and FroYo, I've integrated TSLIB
into Android since I want to be able to support multiple LCD's with a
single image. But your patch definitely gives me a guide on what to
modify in Gingerbread to get the calibration done. My patch from the
previous versions of Android don't work for TSLIB since Gingerbread
has new methods for the input..

-- Ashwin

[Max]

Works great. Thank you.
Why isn't this code integrated in gingerbread?

[ahmed hendy]

thats good but how can i fore this code or running it ?? my android tablet get me depressed because of calibration problem... thanks