Vertical reading direction / Right to left flow not supported with a custom text renderer

[JLL]

I'm trying to use the custom text renderer (from the DirectWrite Hello World sample) in order to render fonts with an outline color different from the fill in. However, when I set the text reading direction and flow vertically (for Japanese), two exceptions are thrown and nothing gets displayed

Exception thrown at 0x7675A6E2 in DWriteHelloWorld.exe: Microsoft C++ exception: OSException at memory location 0x0053EFFC. Exception thrown at 0x7675A6E2 in DWriteHelloWorld.exe: Microsoft C++ exception: [rethrow] at memory location 0x00000000.

I was thinking, maybe the implementation of DrawGlyphRun() is incomplete but the function is actually never called: exception gets thrown before it can call it.

I have attached a patch file (just remove the .txt extension) that enables a quick switch between both behaviors:

• in CustomText.cpp, there are three defines: ISOLATE_CALLS, ENABLE_JAPANESE_TEST, ENABLE_VERTICAL_TEST
• ISOLATE_CALLS will remove all the superfluous calls (font weight, underline, typography etc)
• ENABLE_JAPANESE_TEST will replace the string with some kanjis
• ENABLE_VERTICAL_TEST will enable vertical reading and right to left flow
• I have also added ENABLE_JAPANESE_TEST and ENABLE_VERTICAL_TEST to SimpleText.cpp, showing that without a custom text renderer it works

How to reproduce:

• apply the patch file
• build and run the sample
• you can confirm in the Simple Test tab that vertical orientation works without a custom text renderer
• switch to Custom Text Renderer tab to confirm it is not working
• you can try a different combination of the defines to test the changes

Environment:

• Windows 10 Pro 20H2 build 19042.985
• Windows SDK 10.0.17763.0
• DirectX 12
• Visual Studio Pro 2017

Thank you in advance for the help.

vertical_jp_test_patch.diff.txt

[JLL]

@oldnewthing Sorry for the ping, could someone please take a look at this and confirm? Thank you.