Re: [Freetype] FreeType newbie

[Bruce Mitchener]

Marco,

I use FreeType with Qt as well.  In our application, I just render the 
text directly onto a QPixmap with a bit of code for MacOS X and Windows 
(we don't ship on Unix or embedded platforms).

We use a blending macro derived from some of the FreeType samples:

#define BLEND_COLOR(source, alpha, text) (unsigned char)((alpha * 
(int)(text - source) + 127) / 255);

and on Windows, it looks like this:

    QRgb pixelColor;
    HDC hDC = (HDC)dstPaintDevice.handle();
    const int bitmapRows = bitmap->rows;
    const int bitmapWidth = bitmap->width;
    unsigned char * p = bitmap->buffer;
    for (int yy = 0; yy < bitmapRows; ++yy) {
        for (int xx = 0; xx < bitmapWidth; ++xx) {
            unsigned char pix = *p++;
            if (pix == 255) {
                pixelColor = qRgba(qRed(color), qGreen(color), 
qBlue(color), 0);
            } else {
                QRgb sourceColor = GetPixel(hDC, left + xx, top + yy);
                unsigned char red, green, blue;
                red = qRed(sourceColor);
                red += BLEND_COLOR(red, pix, qRed(color));
                green = qGreen(sourceColor);
                green += BLEND_COLOR(green, pix, qGreen(color));
                blue = qBlue(sourceColor);
                blue += BLEND_COLOR(blue, pix, qBlue(color));
                pixelColor = qRgba(red, green, blue, 0);
            }
            SetPixelV(hDC, left + xx, top + yy, pixelColor);
        }
    }

on OS X, we differ a bit because we use the Carbon API (GetGWorldPixMap, 
GetPixBaseAddr, GetPixRowBytes, along with LockPixels, UnlockPixels).

This code could probably be faster on Windows, but we render a fair bit 
of text and it hasn't yet been a performance issue for us.

We use FreeType 2.18, hand-patched to make the cache system work.

Does this help?

 - Bruce

Marco Mussini wrote:
> Hi all,
> I'm trying to put an antialiased freetype rendered text into QT graphics 
> library. To do this I have an object (called QImage) with 8-bpp depth and 
> gray scale color map in which I have copied pixel per pixel the freetype 
> rendered bitmap. Also in this QImage object I set white background color to 
> be transparent so that it can be overlapped with other objects.
> But there is of course a problem now:
> if image is displayed into a widget with white background it appear fine. But 
> if background is different from white or has many colors (above all dark 
> colors), gray scale pixels that regards antialiasing appears badly.
> For example if my background is dark blue and text is black, image's pixel 
> that regards antialiasing are much more visible and they form a contour for 
> any character of the text.
> How to handle this problem??
>
> I think that a solution could be to set a partial transparency on all
> image's pixel that regard antialiasing, that is all pixels with colors that
> are not black or white.
> I don't know how to do that.
> Does someone knows better techniques to handle this problem??