What are the coordinates of a character origin in GDI with font with not trivial orientation?

Zhivko-2008 20

This question is about the internals of GDI font renderer.

I am converting from GDI (Win32 API) into different drawing format and both formats support character/glyph rotation. I need to calculate the origin of the glyph when the selected font is with orientation different from 90, 180 etc. in order to match the output of ExtTextOut() and related. (The output with degrees 90, 180 etc. does not match the other angles in GDI, this question is not about the trivial cases).

Unfortunately, in GDI font orientation is not a simple rotation, there is some horizontal offset, which likely depends on the glyph size (ink box, not character cell). The GetGlyphOutline() API can be used to get the metrics even for rotated glyphs but does not help with the coordinates of the origin for a given reference point. Other similar APIs ignore font orientation.

Also, if you know a better place to ask this question, please let me know.

1 answer

Jeanine Zhang-MSFT 9,431 Reputation points Microsoft Vendor

2023-10-31T07:19:16.5433333+00:00

Hello,

Welcome to Microsoft Q&A!

GLYPHMETRICS structure contains information about the placement and orientation of a glyph in a character cell.

gmCellIncX：The horizontal distance from the origin of the current character cell to the origin of the next character cell.

gmCellIncY：The vertical distance from the origin of the current character cell to the origin of the next character cell.

You could try to use GetGlyphOutlineA function retrieves the outline or bitmap for a character.

Thank you.

Jeanine

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Zhivko-2008 20 Reputation points

2023-10-31T23:27:59.75+00:00

Thank you, but this gives metrics about the rotated glyph/cell only, not how it is related to the reference point.

For example, if the font is created with CreateFont(100, 0, 0, 450, ...) where would

ExtTextOut(hdc, 0, 0, 0, 0, "V", 1, 0);

put the text (with default DC, i.e. the text alignment is TA_TOP)?

In this case gmCellIncX is 33 and gmCellIncY is -33 (for "Consolas") which is not helping determine where the cell is positioned relative to the reference point (0,0). The actual output seems to put the cell in a rectangle with coordinates around (41, 7, 100, 67) with glyph origin around (80,80).

So far, I figured it is easier to see it as rotation around a point on the cell middle line (in ascent direction) that is on ascent distance from the baseline. Rotating the ascent around such point and offsetting it to allow for the middle of the glyph to be on the baseline works for calculating the vertical offset (Y) of the origin, but the bigger the angle the horizontal offset runs further and further from the point calculated this way.

Thank you for your help.

Jeanine Zhang-MSFT 9,431 Reputation points Microsoft Vendor

2023-11-01T05:47:08+00:00

According to the Doc: Rotating Lines of Text

I agree with you, rotates a character around the center of the client area. And as far as I'm concerned, there is no suitable api to get the coordinates of the reference point when the character is rotated.

Zhivko-2008 20 Reputation points

2023-11-01T05:51:33.33+00:00

That is ok, I can calculate them myself, just need to know how.

What is the algorithm for rotating text with given orientation (when orientation is not in the same direction or perpendicular to escapement)?

Jeanine Zhang-MSFT 9,431 Reputation points Microsoft Vendor

2023-11-01T06:13:58.7333333+00:00

The Windows-API tag is used to handle the issue about how to use the winapi. And as I said, there is no suitable winapi to get what you want. According to your issue, you want to get the algorithm for rotating text, it's beyond the scope of our support.

Zhivko-2008 20 Reputation points

2023-11-01T20:54:05.87+00:00

Do you know a better place to ask this question?

Zhivko-2008 20 Reputation points

2023-11-02T05:32:51.5733333+00:00

The company is MS Partner and we have some product support cases we can open, but I am not sure what category this question qualifies for, could not find anything applicable. Since you understand the question, can you please point me in the right direction?

Zhivko-2008 20 Reputation points

2023-11-02T05:39:24.47+00:00

The company is MS Partner and we can open some product support cases, but I am not sure if this question qualifies and what category it falls into. Seems like all Win API support has disappeared. Since you understand my issue can you point me in the right direction please?

Jeanine Zhang-MSFT 9,431 Reputation points Microsoft Vendor

2023-11-17T02:50:56.0033333+00:00

I fully understand your feelings. But I have to say that the forum Win API support is used to handle the issue about how to use the winapi. The algorithm support is out of the scope. Currently, there is no algorithm forum from Microsoft. You might need to find such places on your own. We can't help about this.

Zhivko-2008 20 Reputation points

2023-11-17T02:58:47.09+00:00

It is not just you unfortunately. Commercial support engineers have no clue either.
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What are the coordinates of a character origin in GDI with font with not trivial orientation?

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