How to use textGravity?

[Airon65]

My attempt is:

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	int w = 800, h = 600;
	
	Magick::Image img5( Magick::Geometry( w, h ), Magick::Color( "white" ) );	
	img5.font( "ComicSans" );
	img5.fontPointsize( 50 );
	img5.fillColor( Magick::Color( "maroon" ) );
	img5.strokeColor( Magick::Color( "red" ) );
	img5.strokeWidth( 2 );
	img5.textGravity( MagickCore::CenterGravity );
	img5.draw( Magick::DrawableText( w / 2, h / 2,  "Some text!" ) );
	img5.write( "images/output.png" );
	

Placing the text with the textGravity = CenterGravity at the center of image: w / 2, h / 2, I expect that image will be placed at the center of the image but it's not It placed at the right bottom side. Why does it work like this?

IM: 7.0.5-2 Q16 x86_64 2017-03-11

[dlemstra]

I think w /2 and h /2 need to be 0 and 0 when you set the textGravity.

[Airon65]

Hm... yeah looks like it works like this

That's not what I was looking for Is it possible to align the text at the center of given coordinates? I mean something like: anchorPointX = 0.5f, anchorPointY = 0.5f. When I use that command: img5.draw( Magick::DrawableText( 100, 200, "Some text!" ) ); I see the text starts drawing from 100x200. I wish to have the center of the text at 100x200.

I can do these steps to achieve that goal:
- Draw text on the temporary image
- trim() it
- Calculate: newX = 100 - ( thatTempImage.columns() / 2 ) and for rows() respectively
- mainImage.composite( thatTempImage, newX, newY, Magick::OverCompositeOp );

but it's.... something strange to me looks too hard for just aligning the text at the center of certain coordinates..

[Airon65]

Well... instead of it I've just developed a formula

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img5.textGravity( MagickCore::CenterGravity );
img5.draw( Magick::DrawableText( 100 - ( w / 2 ), 200 - ( h / 2 ),  "Some text!" ) );

it places a text at the 100x200 by center of it. (anchor point at the center of a text).

[Airon65]

I have a strange problem. Why this code doesn't work?

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std::cout << "Size: " << img5.columns() << "x" << img5.rows() << "\n";	
img5.textGravity( MagickCore::CenterGravity );
img5.draw( Magick::DrawableText( 100 - ( img5.columns() / 2 ), 0,  "Some text!" ) );

It returns me:

libc++abi.dylib: terminating with uncaught exception of type Magick::ErrorDraw: first: non-conforming drawing primitive definition `path' @ error/draw.c/DrawImage/3269
Abort trap: 6

If I have:

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std::cout << "Size: " << img5.columns() << "x" << img5.rows() << "\n";	
img5.textGravity( MagickCore::CenterGravity );
img5.draw( Magick::DrawableText( 100 - ( w / 2 ), 0,  "Some text!" ) ); // "w" defined above and equals to 800

It returns me:

Size: 800x600

But why the first case doesn't work? Why can't I use "img5.columns()" in my calculations as the argument? What's the magic?