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
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