Font Metrics

[ChasW]

Would there happen to be a font metrics related function that would return an array of values corresponding to the cumulative string widths for each character position in a string? i.e. similar to Win32's GetTextExtentExPoint

Thanks in advance,
Charles

[Chicken Blood Machine]

No. You will have to use QFontMetrics::width() in a loop to generate the cumulative values, e.g:



std::vector<int> charExtents;
QFontMetrics fm(font());
for (int n = 0; n < text.length(); ++n)
charExtents.push_back(fm.width(text, n));

[ChasW]

No. You will have to use QFontMetrics::width() in a loop to generate the cumulative values, e.g:



std::vector<int> charExtents;
QFontMetrics fm(font());
for (int n = 0; n < text.length(); ++n)
charExtents.push_back(fm.width(text, n));


Just for clarification, given the code above, doesn't the first character in the string get skipped? In other words, for length "0" which is what n would be for the first iteration, on my system, width() is returning 0. As well the final value is not being stored. Is that what should be happening?

example: using the above code on my system, given that text is a string "abc" for a fixed font whose width is 7 pixels, my vector is getting these values, 0, 7, 14.

In order to get the 0th element of the charExtents vector to be the pixel width for that character, I am using fm.width(text, n+1). In other words, to get 7, 14, 21.

Is this correct, or could I be doing something wrong?

Thank you in advance for any clarification.

[wysota]

Use
charExtents.push_back(fm.width(text[n])); instead.

[ChasW]

Use
charExtents.push_back(fm.width(text[n])); instead.

Given the above string, this populates the vector with 7,7,7

I was just looking for a clarification as to how to correctly get 7, 14, 21.

I think my observation above was a correct one.

My specific question is this: given the docs here http://doc.trolltech.com/4.2/qfontmetrics.html#width

We know what happens when the int len is -1, but what about the case of int len is 0. Can we assume that when we pass 0 for len that we will always get 0 in return?

[wysota]

Yes, I think it is safe to assume that :)

EDIT:
And if you don't want to "assume", but "be sure" instead, just look into the sources:

int QFontMetrics::width(const QString &str, int len) const
{
if (len < 0)
len = str.length();
if (len == 0)
return 0;
//...

[Chicken Blood Machine]

Just for clarification, given the code above, doesn't the first character in the string get skipped? In other words, for length "0" which is what n would be for the first iteration, on my system, width() is returning 0. As well the final value is not being stored. Is that what should be happening?

example: using the above code on my system, given that text is a string "abc" for a fixed font whose width is 7 pixels, my vector is getting these values, 0, 7, 14.

In order to get the 0th element of the charExtents vector to be the pixel width for that character, I am using fm.width(text, n+1). In other words, to get 7, 14, 21.

Is this correct, or could I be doing something wrong?

Thank you in advance for any clarification.

Yes, you're right. It should be:


std::vector<int> charExtents;
QFontMetrics fm(font());

for (int n = 0; n < text.length(); ++n)
charExtents.push_back(fm.width(text, n + 1));