Millisecond Forums

Your calibration logic is fine. You can see this by displaying e.g. a rectangle sized according to expressions.letters on-screen and measuring its dimensions (it's the desired 12mm on my system and should be on yours as well):


<<<<this script should always shows letter 12mm height, regardless of participants computer display properties>>>
<values calibration>
/ cal_mm = 0mm
/ cal_px = 500px
/ letters = 12mm
</values>

<expressions>
/ mmtopx = values.cal_mm/values.cal_px
/ letters = 1px*round((values.letters/expressions.mmtopx))
</expressions>

<openended calibrate>
/ stimulusframes = [1= line]
/ position = (50%, 80%)
/ validresponse = (anyresponse)
/ monkeyresponse = ("195")
/ mask = positiveinteger
/ ontrialend = [values.cal_mm=openended.calibrate.response]
/ ontrialbegin = [openended.calibrate.buttonlabel= "Save results (in mm)"]
</openended>

<shape line>
/ shape = rectangle
/ color = (black)
/ erase = (250,250,250)
/ size = (values.cal_px,10px)
/ position = (50%, 50%)
/ halign = center
</shape>

<text Letters>
/ items = ("F","P","Q","J","H","K","T","S","N","R","Y","L")
/ fontstyle = ("Verdana", expressions.letters, true)
/ erase = true(silver)
</text>

<trial trial_A>
/stimulustimes = [0=letters, myshape]
/ validresponse = (57)
</trial>

<shape myshape>
/ shape = rectangle
/ size = (expressions.letters, expressions.letters)
/ position = (50%, 25%)
/ color = red
</shape>

<block calibrate>
/trials = [1=calibrate]
</block>

<block block_trial_A>
/trials = [1-10=trial_A]
</block>

<expt >
/blocks = [1=calibrate;2=block_trial_A]
</expt>

The problem with your approach is that fonts just don't work that way. To the best of my knowledge, there is no such thing as a "fixed-height" font, i.e. letters *will* necessarily vary in height due to their natural shape. For example, the letter Q requires more vertical space than the letter P (the red square is 12mm x 12mm):

If you measure the height of the Q, you'll find it to be relatively close to 12mm (also note that there's typically some amount of empty space around letters in a font).

If you really want all your letters to have identical, fixed height you will have to resort to a different approach. E.g. don't use fonts, but prepare images displaying the letters, with each letter sized according to your needs.

Thanks, a lot Dave.

You are right, it looks like there is no fixed font size
So in this situation, It is good idea to use picture instead of fonts.

Thanks for advice :)

To clarify, there are so-called "fixed-width" aka. "monospaced" fonts (Consolas, Courier New, etc.), meaning that each letter's bounding rectangle takes up the same amount of horizontal space. The effect is that the string "IIII" takes up the same amount of horizontal space as the string "OOOO", which is not the case for "normal" fonts:

<trial mytrial>
/ stimulusframes = [1=fixedwidth, notfixedwidth]
/ validresponse = (57)
</trial>

<text fixedwidth>
/ items = ("OOOO~nIIII")
/ fontstyle = ("Courier New", 5%)
/ position = (40%, 50%)
</text>

<text notfixedwidth>
/ items = ("OOOO~nIIII")
/ fontstyle = ("Verdana", 5%)
/ position = (60%, 50%)
</text>



But something like a "fixed-height" font does not exist (to the best of my knowledge). Even in monospaced fonts, vertical space typically differs between letters due to shape: