Update the 'Using Fonts' page to include information on spacing adjustments and kerning pairs for image fonts (#10880)

* Update the 'Using Fonts' page to include information on spacing adjustments and kerning pairs for image fonts

Closes https://github.com/godotengine/godot-docs/issues/10855

Non-monospaced image fonts have been supported for quite some time, but the documentation has not yet been updated to reflect this.

There are now some additional screenshots and examples of how to use the extra parameters in the Character Ranges, and how to use the Kerning Pairs list.

tutorials/ui/gui_using_fonts.rst

@@ -68,17 +68,16 @@ Godot supports the BMFont (``.fnt``) bitmap font format. This is a format create
 by the `BMFont <https://www.angelcode.com/products/bmfont/>`__ program. Many
 BMFont-compatible programs also exist, like `BMGlyph <https://www.bmglyph.com/>`__ or web-based `fontcutter <https://github.com/fabienbk/fontcutter>`__.
 
-Alternatively, you can import any image to be used as a bitmap font. This is
-only supported for **monospaced** fonts (fonts where each character has the same
-width). To do so, select the image in the FileSystem dock, go to the
-Import dock, change its import type to **Font Data (Monospace Image Font)** then
+Alternatively, you can import any image to be used as a bitmap font.
+To do so, select the image in the FileSystem dock, go to the
+Import dock, change its import type to **Font Data (Image Font)** then
 click **Reimport**:
 
 .. figure:: img/using_fonts_bitmap_font_from_image_import_options.webp
    :align: center
-   :alt: Changing import type to Font Data (Monospace Image Font)
+   :alt: Changing import type to Font Data (Image Font)
 
-   Changing import type to **Font Data (Monospace Image Font)**
+   Changing import type to **Font Data (Image Font)**
 
 The font's character set layout can be in any order, but orders that match
 standard Unicode are recommended as they'll require far less configuration to
@@ -122,6 +121,33 @@ If your font image contains guides (in the form of lines between glyphs) or
 if spacing between characters appears incorrect, try adjusting **Character
 Margin**. This margin is applied for every imported glyph.
 
+If you need finer control over character spacing than
+what the **Character Margin** options provide, you have more options.
+
+For one, **Character Ranges** supports 3 additional arguments after the
+specified range of characters.
+These additional arguments control their positioning and spacing.
+They represent space advance, X axis offset, and Y axis offset in that order.
+They will change the space advance and offset of each character
+by the amount of pixels written. Space advance is most useful if, for example,
+your lowercase letters are thinner than your uppercase letters.
+
+.. figure:: img/using_fonts_bitmap_font_advance_offsets_diagram.webp
+   :align: center
+   :alt: Diagram showing the advance and offset values being used in character ranges.
+
+   Do note that the offsets can cause your text to be cropped off the edge of your label boundaries.
+
+Secondly, you can also set up **Kerning Pairs** for individual characters.
+Specify your kerning pair by typing two sets of characters separated by a space,
+then followed by another space, a number to specify how many extra/less pixels to
+space those two sets of characters when placed next to each other.
+
+.. figure:: img/using_fonts_bitmap_kerning_pairs_example.webp
+
+If needed, your kerning pair characters can be specified by Unicode character code
+by entering ``\uXXXX`` where XXXX is the hexadecimal value of the Unicode character.
+
 Loading a font file
 -------------------