Wrong horizontal character positioning in hello world examples

[badicsalex]

The left bearing is not used in these examples (pyright does complain about this):

freetype-py/examples/hello-world.py

Line 42 in 51ee6e1

left = slot.bitmap_left

freetype-py/examples/hello-world-cairo.py

Line 47 in 51ee6e1

left = slot.bitmap_left

And probably some other places. This should probably fixed, because it is common practice to start out from examples and build from there.

Example with the Good Times font; notice that the distance between MP and TI are way off:

The correct rendering looks like this:

[rougier]

Thansk for the report. For the correct rendering, did you do it with freetype-py (i.e. do you have a fix ?)

[HinTak]

The full fix is probably something close to what I did here:
https://github.com/HinTak/harfbuzz-python-demos/blob/38f4c107f37c518a2f028bf7031ae3c306ae1311/hb-view.py#L198

hb-view.py was written to explicitly support Arabic and Hebrew fonts, where non-zero left-side bearing (and top/bottom-side bearings too) are common.

That said, I think the original example works as it is, for a font that mostly have zero left-side bearing. For those who think they need non-zero leftside/topside bearings, like Arabic users, they know they need to add it anyway.

I am more inclined to say add a new example using a different font - or even refer to my repo, instead of bloating the existing one.

[badicsalex]

Thansk for the report. For the correct rendering, did you do it with freetype-py (i.e. do you have a fix ?)

I basically changed this line:

freetype-py/examples/hello-world.py

Line 47 in 51ee6e1

Z[y:y+h,x:x+w] += numpy.array(bitmap.buffer, dtype='ubyte').reshape(h,w)

to

 Z[y:y+h,x+left:x+w+left] += numpy.array(bitmap.buffer, dtype='ubyte').reshape(h,w)

It worked for my case, but for negative left values, it would probably be incorrect.

For those who think they need non-zero leftside/topside bearings, like Arabic users, they know they need to add it anyway.

Well, my font and text was western, so I didn't know I had to add it.

[HinTak]

Arabic fonts have top/bottom bearings too. While I agree the example is limited, I think it is best to create a new example using a font with obviously non-zero left bearings. Perhaps one cursive font.

[rougier]

A new example might help to show the problem. But as shown by @badicsalex, the simple hello-world rendering is wrong. I would add the left bearing with a comment warning this is not the correct way to do tue and redirect reader to your hb-view.py example.

[HinTak]

I wonder if any of the glyphs in "Hello World" has a non-zero leftside bearing, in the example font. That's basically my question. A future contributor might decide to "simplify" the code if it is all zeros.

While working on the hb-view example (I thought of contributing that to freetype-py but it has extra dependencies on harfbuzz, which is another thing) , I remember there is a rather big omission to the hello world example - none of "Hello World" has a descender part below the baseline, so it does not allocate drawing space below the baseline. This is quite unusual - longer normal run of texts have a "g" or a "y". This (the example does not allocate drawing space below baseline, so "y", and "g" are cut off, if you put one in) probably could go in as a comment as well.

[badicsalex]

In any case, the original lines I linked are dead code since the left variable is not used afterwards, so these should be deleted.

I think the above mentioned comments or something like a generic warning should be added at least, even if the code isn't touched for simplicity.

[rougier]

@HinTak You're right. This hello-world.py example is really bad (my fault). As mentioned by @badicsalex, people will probably use it as a start and extend from it but, if is wrong from the start, it is a problem. We can modify the text to include some g/j/y and add the left bearing. It won't be perfect but at least not totally wrong.

[HinTak]

I only found one other problem like this, in hello-vf.py . Most of the other examples seem to use the left side bearing value - or at least, not obviously not using it.

Actually the left side bearings of the example are mostly non-zero - and illustrates the problem better than the Good Times font (most of them 1 or two pixels off) - the "!" at the end of "Hello World !" was off by 7 pixels.

I did compare the result with hb-view.py (that gets the leftside bearings from harfbuzz instead of freetype).

I re-check the descender comment - I think it probably concerns another example instead of hello-world.