Re: [ft] Using different loading and render modes, plus LCD example

[Aekold Helbrass]

Thank you, finally figured out how to use LCD bitmap with QImage.
Small piece of source code below. But still have a problem: there is a
lot of noise on rendering, and that noise is jumping on repainting of
component. So it looks like I've done something wrong with color
transformations. Basically I am filtering out white pixels, but there
are a lot of "almost white" ones. Please see attachment.

source code (cut out error handling to show only logic part):

            error = FT_Load_Glyph( m_face, glyph_index, FT_LOAD_TARGET_LCD);
            error = FT_Library_SetLcdFilter(m_library, FT_LCD_FILTER_DEFAULT);
            error = FT_Render_Glyph( m_face->glyph, FT_RENDER_MODE_LCD );

            int _h = m_face->glyph->bitmap.rows;
            int _w = m_face->glyph->bitmap.width/3;
            int _p = m_face->glyph->bitmap.pitch;

            uchar *src = m_face->glyph->bitmap.buffer;
            glyphImage = new QImage(_w, _h, QImage::Format_ARGB32);

            int bit = 0; // address in buffer
            for (int y = 0; y < _h; y++) {

                for (int x = 0; x < _w; x++) {

                    uchar r = 0xff - src[bit++];
                    uchar g = 0xff - src[bit++];
                    uchar b = 0xff - src[bit++];

                    // filtering out any whites:
                    if (r + g + b >= 3 * 0xff) {
                        continue;
                    }

                    glyphImage->setPixel(x, y, qRgb(r, g, b)); //
pixel coordinates to color value

                }

                bit = _p * (y + 1); // go to next line, start from 0
            }

On Wed, Jun 15, 2011 at 7:20 PM, Collyer, Oliver, SI
<address@hidden> wrote:
> The light hinting more or less just hints in the vertical direction, so this 
> is compatible with LCD rendering which deals with the horizontal (assuming 
> your LCD display is a regular one and your text is horizontal). IMO it's a 
> pretty good combination.
>
> To display an LCD-rendered source bitmap on the screen you basically use each 
> triplet of values in the source as the respective intensity/alpha values of 
> the RGB components of your destination pixel.
>
> i.e:
>
> - the first (left) value in the source triplet gives how much of the R of 
> your text colour to use when blending (so a value of 255 means use all of the 
> text colour R and don't mix it with any of the background bitmap R, whereas a 
> value of 128 would mean mix them 50-50, etc)
> - the second (middle) value in the source triplet gives how much of the G of 
> your text colour to use when blending
> - the third (right) value in the source triplet gives how much of the B of 
> your text colour to use when blending
>
> This assumes you have already filtered your LCD bitmap first. FreeType has 
> functionality for doing this, and this basically reduces a problem known as 
> 'colour fringing' by mixing together neighbouring pixels in the bitmap.
>
> Here is a decent resource that describes the basics:
>
> http://www.grc.com/ctwhat.htm
>
> Hope this helps.
>
> On 15 Jun 2011, at 18:58, Aekold Helbrass wrote:
>
>> Good day All!
>>
>> I've read the note to
>> http://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html#FT_LOAD_TARGET_XXX
>> and now I have a question: what will I get in case of using LIGHT for
>> loading and LCD for rendering? Is it considered bad practice, or it
>> may be used to achieve some special results?
>>
>> And the second question - the reason why I can't check the first one
>> for myself. I am using that awesome Qt example (example4.cpp) to see
>> how freetype works in general, but I can't get proper LCD modes. I see
>> that image is 3 times wider and divide it, but it's still crippled
>> when rendered. I suppose I should use some other color table or some
>> smart pixel filtering methods that are used in openjdk or qt, but I am
>> not familiar with freetype enough to figure it out myself. So, if
>> there are some LCD rendering examples or guides - please give me some
>> links.
>>
>> Thanx!
>>
>> _______________________________________________
>> Freetype mailing list
>> address@hidden
>> https://lists.nongnu.org/mailman/listinfo/freetype
>
>

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