Fix DirectWrite raster_bounds arithmetic

[idursun]

Fixes #85

• raster_bounds was returning a rectangle at origin (0,0) whereas the origin of the bounds rectangle returned by get_alpha_texture_bounds is not (0,0). This caused offsetting origin calculation to be off when passed to rasterize_glyph which caused the clipping.

Offsetting origin calculation that I am referring to is:

https://github.com/pcwalton/font-kit/blob/6801dce15cbc75448d99420eeebbe8c867585f36/examples/render-glyph.rs#L133-L136

This change sets the origin of the raster_bounds rectangle so that the origin offset arithmetic actually holds for directwrite.

c:\repositories\rust\font-kit>cargo run --example render-glyph ArialMT { 32
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target\debug\examples\render-glyph.exe ArialMT { 32`
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[RazrFalcon]

I've tested it with silicon and looks like everything is fine. Could you add some tests, especially for the { case?

[idursun]

Sure 👍

Similar to the rasterization tests (i.e. rasterize_glyph_with_grayscale_aa, rasterize_glyph_bilevel) that are asserted with check_L_shape?

[RazrFalcon]

Yes, I think this will work well.

[idursun]

I have added a "best-effort" test for verifying the rasterization of any top-down symmetrical letters.

Currently, it's only testing { letter and running against windows and mac. Although, I believe it should kinda work against all loaders.

[RazrFalcon]

I think this is good enough. Thanks again!

[idursun]

Changed to target only Windows. Apparently, macos glyph is not as symmetrical.

[pcwalton]

Thanks!