Re: [ft] anti-aliasing question

[Dave Calkins]

If that fails, could you perhaps attach some sample
renderings in png format?


  

In order to try and factor out any effect of the GL side of things, I wrote a small stand-alone windows app which just loads a font, renders a single glyph, and then writes out the rendered bitmap in the glyph slot to a .png and .txt file.  So there's nothing here but calling FreeType and then storing the resultant gray scale bitmap.

At first I didn't see a huge difference, but this was before changing the flags Werner suggested.  I changed those (to ensure the byte code interpreter is enabled) and rebuilt this sample and it does look a little different.  The text is brighter, so maybe there's a darkening happening when rendering to GL.

The FreeTypeGL rendering code is shown below.  Its storing the gray scale image in a texture which gets treated as the alpha channel to render a solid rectangle.  Since I'm doing 2D rendering with GL, there should be a 1-to-1 between the rendered pixels and the texture pixels so I don't believe any texture filtering should be ocurring.

>>> setup the texture for the glyph

    err = FT_Render_Glyph(glyph, FT_RENDER_MODE_NORMAL);
    FT_Bitmap      bitmap = glyph->bitmap;
    destWidth  = bitmap.width;
    destHeight = bitmap.rows;

    if(destWidth && destHeight)
    {
        glPushClientAttrib(GL_CLIENT_PIXEL_STORE_BIT);
        glPixelStorei(GL_UNPACK_LSB_FIRST, GL_FALSE);
        glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

        glBindTexture(GL_TEXTURE_2D, glTextureID);
        glTexSubImage2D(GL_TEXTURE_2D, 0, xOffset, yOffset, destWidth, destHeight, GL_ALPHA, GL_UNSIGNED_BYTE, bitmap.buffer);

        glPopClientAttrib();
    }


//      0
//      +----+
//      |    |
//      |    |
//      |    |
//      +----+
//           1

    uv[0].X(static_cast<float>(xOffset) / static_cast<float>(width));
    uv[0].Y(static_cast<float>(yOffset) / static_cast<float>(height));
    uv[1].X(static_cast<float>(xOffset + destWidth) / static_cast<float>(width));
    uv[1].Y(static_cast<float>(yOffset + destHeight) / static_cast<float>(height));

    corner = FTPoint(glyph->bitmap_left, glyph->bitmap_top);

>>> render the glyph texture

    float dx, dy;

    if(activeTextureID != glTextureID)
    {
        glBindTexture(GL_TEXTURE_2D, (GLuint)glTextureID);
        activeTextureID = glTextureID;
    }

    dx = floor(pen.Xf() + corner.Xf());
    dy = floor(pen.Yf() + corner.Yf());

    glBegin(GL_QUADS);
        glTexCoord2f(uv[0].Xf(), uv[0].Yf());
        glVertex2f(dx, dy);

        glTexCoord2f(uv[0].Xf(), uv[1].Yf());
        glVertex2f(dx, dy - destHeight);

        glTexCoord2f(uv[1].Xf(), uv[1].Yf());
        glVertex2f(dx + destWidth, dy - destHeight);

        glTexCoord2f(uv[1].Xf(), uv[0].Yf());
        glVertex2f(dx + destWidth, dy);
    glEnd();

    return advance;

glyph.png
Description: PNG image

glyph.txt
Description: Text document

main.cpp
Description: Text document

main.h
Description: Text document

SaveToPNG.cpp
Description: Text document

SaveToPNG.h
Description: Text document

SaveToTXT.cpp
Description: Text document

SaveToTXT.h
Description: Text document