#1435 Scintilla5 in Notepad++: Text is mirrored in RTL

[Yaron]

STR:
Paste Hello in Notepad++.
Change direction to RTL.

Result:
The text is mirrored.

https://github.com/notepad-plus-plus/notepad-plus-plus/blob/b4a58429c3c8f7fe3250aa4a0e57743c2bceaf3a/PowerEditor/src/NppCommands.cpp#L3530

Does not fix the issue with Scintilla5.

[Yaron]

Using https://github.com/notepad-plus-plus/notepad-plus-plus/commit/b4a58429c3c8f7fe3250aa4a0e57743c2bceaf3a

See also: https://github.com/notepad-plus-plus/notepad-plus-plus/issues/11476

[Neil Hodgson]

Scintilla only (experimentally) supports bidirectional text with the SCI_SETBIDIRECTIONAL API.

I suspect what you are seeing is Notepad++ setting a text direction with WS_EX_LAYOUTRTL or WS_EX_RTLREADING or similar on a Scintilla window. Scintilla has never actively supported this and any past success with these modes was accidental. May have worked with GDI drawing but not DirectWrite.

[rdipardo]

I suspect what you are seeing is Notepad++ setting a text direction with WS_EX_LAYOUTRTL . . .

Browsing commit 7fa6fb083b0 confirms that is the case:

void ScintillaEditView::changeTextDirection(bool isRTL)
{
    long exStyle = static_cast<long>(::GetWindowLongPtr(_hSelf, GWL_EXSTYLE));
    exStyle = isRTL ? (exStyle | WS_EX_LAYOUTRTL) : (exStyle & (~WS_EX_LAYOUTRTL));
    ::SetWindowLongPtr(_hSelf, GWL_EXSTYLE, exStyle);
    // ...
}

[Zufu Liu]

That does not work as expected, see https://github.com/zufuliu/notepad2/issues/392

[Yaron]

Neil,

Thank you for the detailed and useful reply.
I'd like to thank you also for the Scintilla project. I appreciate your work.

Please consider this thread as another request for a better RTL support. :)

---

Robert & Zufu,

Thank you for the additional info.

[Neil Hodgson]

I don't think this is describing a feature that can be implemented.

[Neil Hodgson]

May be fixed with [fa80f5].

[Zufu Liu]

It seems adding a 90 degrees transform (in ScintillaWin::EnsureRenderTarget()) will make Technology::DirectWriteDC rendered into same thing as GDI.

// test code, need to load D2D1MakeRotateMatrix() and check window layout
#pragma comment(lib, "D2d1.lib")
pRenderTarget->SetTransform(D2D1::Matrix3x2F::Rotation(90.0f, D2D1::Point2F(0.0f, 0.0f)));

Edit: this does work, nothing is rendered.

[Neil Hodgson]

A 180 degree rotation is more likely wanted than 90 but that inverts the y axis.

This code inverts x for Technology::DirectWriteDC but then the text is no longer on the right:

D2D1::Matrix3x2F invertX = D2D1::Matrix3x2F(-1, 0, 0, 1, 0, 0);
D2D1::Matrix3x2F moveX = D2D1::Matrix3x2F::Translation(rc.right - rc.left, 0);
pRenderTarget->SetTransform(invertX * moveX);

For WS_EX_LAYOUTRTL the IDWriteTextFormat::SetReadingDirection API is likely the key.
https://docs.microsoft.com/en-us/windows/win32/directwrite/how-to-ensure-text-is-displayed-with-the-correct-reading-direction

Code from Raghda's bidi work:

 void SurfaceD2D::DrawTextCommon(PRectangle rc, Font &font_, XYPOSITION ybase, std::string_view text, UINT fuOptions) {
    SetFont(font_);

@@ -1542,6 +1994,11 @@
            D2D1_RECT_F rcClip = {rc.left, rc.top, rc.right, rc.bottom};
            pRenderTarget->PushAxisAlignedClip(rcClip, D2D1_ANTIALIAS_MODE_ALIASED);
        }
+       if (bidiR2L) {
+           pTextFormat->SetReadingDirection(DWRITE_READING_DIRECTION_RIGHT_TO_LEFT);
+       } else {
+           pTextFormat->SetReadingDirection(DWRITE_READING_DIRECTION_LEFT_TO_RIGHT);
+       }

        // Explicitly creating a text layout appears a little faster
        IDWriteTextLayout *pTextLayout;

[Zufu Liu]

SetReadingDirection() has no effect.

pfm->pTextFormat->SetReadingDirection(mode.bidiR2L ? DWRITE_READING_DIRECTION_RIGHT_TO_LEFT : DWRITE_READING_DIRECTION_LEFT_TO_RIGHT);

however SetLayout(hdc, LAYOUT_BITMAPORIENTATIONPRESERVED); can be added into ScintillaWin::PaintDC() to make all DirectWrite technologies behaviors same (no RTL), which is documented at https://docs.microsoft.com/en-us/windows/win32/api/d2d1/nn-d2d1-id2d1dcrendertarget#id2d1dcrendertargets--gdi-transforms--and-right-to-left-language-builds-of-windows

[Neil Hodgson]

SetReadingDirection inside SurfaceD2D::DrawTextCommon can only affect one lexeme.

Here is a mixed language and mixed direction comment which is a single lexeme with DWRITE_READING_DIRECTION_LEFT_TO_RIGHT (top) and DWRITE_READING_DIRECTION_RIGHT_TO_LEFT (bottom):

[Zufu Liu]

move rotation local into SurfaceD2D::DrawTextCommon() has some effects for SC_TECHNOLOGY_DIRECTWRITEDC.

const D2D1_POINT_2F origin = DPointFromPoint(Point(rc.left, ybase - pfm->yAscent));
//DWRITE_TEXT_METRICS textMetrics{};
//pTextLayout->GetMetrics(&textMetrics);
//const FLOAT width = textMetrics.widthIncludingTrailingWhitespace + 24.0f;
const FLOAT width = static_cast<FLOAT>(rc.Width());
D2D1::Matrix3x2F invertX = D2D1::Matrix3x2F(-1, 0, 0, 1, 0, 0);
D2D1::Matrix3x2F moveX = D2D1::Matrix3x2F::Translation(width, 0);
pRenderTarget->SetTransform(invertX * moveX);
//pRenderTarget->SetTransform(D2D1::Matrix3x2F::Rotation(180.0f, DPointFromPoint(rc.Centre())));
//pRenderTarget->SetTransform(D2D1::Matrix3x2F::Rotation(180.0f, origin));
pRenderTarget->DrawTextLayout(origin, pTextLayout, pBrush, d2dDrawTextOptions);
ReleaseUnknown(pTextLayout);
pRenderTarget->SetTransform(D2D1::Matrix3x2F::Identity());

[Yaron]

@nyamatongwe,

Thanks again for the fix. I appreciate it.

@zufuliu,

Thank you for the interesting info.