Re: [ft] How to draw FT_Bitmap to the ARGB image?

[John Found]

On Thu, 5 Nov 2015 13:05:43 +0100
Wojciech Mamrak <address@hidden> wrote:

> > In a result I made it first to convert the RGB glyph to grayscale and
> > then to blend it to the background. This way, the transparency is always OK.
> 
> You can return grayscale bitmaps from FT directly, without the
> conversion on your side.
> The transparency will be OK but remember to use the alpha channel
> blending formula this time :)

I am writing a GUI library and the user later will choose how FT fonts to be 
rendered.
So, I need to provide support for all possible formats.

For the grayscale rendered glyphs, I am using the value as a "intensity", 
multiplying
by it every component of the the drawing color:

Crgb = Crgb * Gray and then making the standard alpha blending of so computed 
color and
the background. Everything seems to work fine...

Now I am using the same algorithm for LCD rendered glyphs, only computing the 
gray value
by a little bit weird equation: Gray = (R + 2*G + B)/4 and the result is also 
pretty good.

> 
> > But the big question is "Do I need subpixel antialiased fonts so badly?" :)
> 
> This question holds if you intend to compose and display some images
> on the screen (which is always opaque). Then it depends on font size,
> font itself, targeted device (e.g. resolution, pixel layout), etc. If
> you intend to save images with transparency, the only versatile option
> is grayscale antialiased text. Generating SVG images, which are
> composed "at runtime", assuming rendering engine supports
> subpixel-antialiased text, is another option.
> 

It depends greatly on the use cases of the library.

But as long as it is not finished yet, I can say only that it is intended to
be used for GUI creation on x86 computers, working under different OSes.


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John Found <address@hidden>