For DirectWrite, how we can placea text by specifying the position of the baseline?

Question

Hi,

I want to know, for DirectWrite, how I can place text by specifying the position of the baseline.

I see both ID2D1RenderTarget::DrawText() and ID2D1RenderTarget::DrawTextLayout() calculate the position of the text to fit into the bounding box given by the parameter by default. It looks IDWriteTextFormat::SetLineSpacing() can modify the behavior but I couldn't figure out how I actualy can use it for my purpose.

We could do this by specifying TA_BASELINE to SetTextAlign() for TextOut(). I'm looking for the something similar.

-Takuji

Answer 1

Takuji,

I'm looking at the same issue. Did you ever figure this out and would you mind sharing?

Many thanks

Answer 2

Hi GSP_T,

My solution is bit redundant but the solution that I got is:

...
//calculate font metrics
    DWRITE_FONT_METRICS fontMetrics;
    font->GetMetrics(&fontMetrics);  //font is the object of IDWriteFont uses for the text rendering.
    ascent = MulDiv( fontMetrics.ascent, fontSize,fontMetrics.designUnitsPerEm);
    descent = MulDiv(fontMetrics.descent, fontSize,fontMetrics.designUnitsPerEm);	
	
...
	
// Specify the baseline of the text explicitly	
    textFormat->SetLineSpacing(DWRITE_LINE_SPACING_METHOD_UNIFORM, ascent + descent, ascent);    // textFotmat is the object of IDWriteTextFormat used for text rendering.
	
...
	
// Calculate layoutY from the baseLineY 	
	layoutY =  baseLineY - ascent;
	
// Render the text using layoutY 
...
	

The real code that I have caches the metrics of the font and bit more complecated but the code above explains the idea enough I think.

HTH

Takuji

Answer 3

Thanks, I'll have to look at this later. I'm working on some other problems and will get back to this at some point.

Again, thanks