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Re: [ft] a confusing problem when using FT_Library_SetLcdFilterWeights()

From: Werner LEMBERG
Subject: Re: [ft] a confusing problem when using FT_Library_SetLcdFilterWeights();
Date: Sun, 29 Apr 2018 06:49:57 +0200 (CEST)


> I am a chinese programmer. I want to output text on OpenGLES with
> freetype(C++).  What's more, I want to use that class (C++) in our
> production.  It's handle frequency spectrum analyzer.  But now I an
> confused about a problem.  I set the subpixel choice before building
> lib and my display is LCD display.
> Firstly, I write a small demo in our WindowCE7.0 platform and it
> works correctly.  I use the LCD filter like this.
>   FT_Library_SetLcdFilter(library, FT_LCD_FILTER_LIGHT);
>   unsigned char weight = 0x55;
>   FT_Library_SetLcdFilterWeights(library, &weight);
> The result is picture1.

Unfortunately, such hand-held camera snapshots are not very helpful in
analyzing your problem.  Can't you simply press the `PrtScr' button to
get real screen snapshots that you can further process to get PNG

> However, when I add the Class to our spectrum analyzer, it seems not
> working correctly.  The result is picture2.  It seem like more
> darker than picture1.  [...]

I doubt that such an issue happens on your WindowCE platform only.
Please compile your program on standard Windows, say, and check
whether you have the same issues – and maybe this enables you to get
real screendumps...

I also suggest that you play around with the `ftview' demo program
(which allows full control over LCD weights), also checking its source


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