C++ OpenGL / FreeType scrolling font

Looking for opinions on the best way to scroll text, Im using the freetype lib with OpenGL/c++ on Slackware.

I am basically using the nehe example for the freetype se开发者_JAVA技巧tup/print methods. http://nehe.gamedev.net/tutorial/freetype_fonts_in_opengl/24001/

So say for example, i wanted some text to slowly erode from the bottom up,pixel by pixel, any ideas?

Although i have not fully examined their code, would it be best to alter the TexCoord/Vertex data?

glBegin(GL_QUADS);
glTexCoord2d(0,0); glVertex2f(0,bitmap.rows);
glTexCoord2d(0,y); glVertex2f(0,0);
glTexCoord2d(x,y); glVertex2f(bitmap.width,0);
glTexCoord2d(x,0); glVertex2f(bitmap.width,bitmap.rows);
glEnd();
glPopMatrix();
glTranslatef(face->glyph->advance.x >> 6 ,0,0);

Any advise at all would be helpful

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You could use clip planes for that. They will determine the area where the text will be rendered. You can move the clip planes each frame so that clipped/visible area is changes and your text will slowly erode from the bottom up, pixel by pixel.

This code clips the text from right and left:

procedure TRenderUI.SetupClipX(X1,X2:smallint);
var cp:array[0..3]of real; //Function uses 8byte floats //ClipPlane X+Y+Z=-D
begin
  glEnable(GL_CLIP_PLANE0);
  glEnable(GL_CLIP_PLANE1);
  FillChar(cp, SizeOf(cp), 0);
  cp[0] := 1; cp[3] := -X1; //Upper edge
  glClipPlane(GL_CLIP_PLANE0, @cp);
  cp[0] := -1; cp[3] := X2; //Lower edge
  glClipPlane(GL_CLIP_PLANE1, @cp);
end;

//Release all clipping planes
procedure TRenderUI.ReleaseClip;
begin
  glDisable(GL_CLIP_PLANE0);
  glDisable(GL_CLIP_PLANE1);
end;

You can use up to 4 clipping planes simultaneously.