Fix overflow #8
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Fix overflow #8
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The calibration variables _cal_vi1 and _cal_vj1 were uint16_t, but this led to overflow on my screen, making the touch x-position jump from around 100 to 56,000 in the lower 25% of the screen. Changing these variables to int32_t fixes this overflow.
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I had a weird issue with my TJCTM24028-SPI (cheap eBay touch screen + TFT) and this library. When touching the lower 25% of the screen, the XPTPaint program worked ok, but when going into the top 75% the lines jumped off the screen and were not where my finger was touching. I tracked down the cause (or, at least, the change that fixes this) to the calibration variables
_cal_vi1and_cal_vj1. These were previously set touint16_t, but are used in a calibration operation involvingint32_tnumbers, potentially leading to overflow (as in my case). Changing these variables toint32_tfixes this overflow, and solves the problem on my screen with discontinuities.