Hello all,
i get curious distortions while scaling textures down to use them as image pyramid.
For that i do:
1) Write data from host into a texture buffer (glDrawPixels or glTexSubImage2D).
2) This texture is used for the next scale level. So i apply it and draw a quad with:
glBegin(GL_QUADS);
{
// draw first scale
glTexCoord2f(0.0,0.0);
glVertex3f(-1.0,-1.0,1.0f); // down left
glTexCoord2f(1.0,0.0);
glVertex3f(0.0,-1.0,1.0f); // down right
glTexCoord2f(1.0,1.0);
glVertex3f(0.0,0.0,1.0f); // up right
glTexCoord2f(0.0,1.0);
glVertex3f(-1.0,0.0,1.0f); // up left
}
glEnd();
Please note that glVertex3f is getting parameters for only a fourth of the texture buffer. The rest of the buffer is used for the next scale levels.
The data I draw contains only a simple rectangle. I have also applied different scaling filters. In the following image, you see a bilinear kernel applied to the down scale procedure. What i get is a distortion while crossing the diagonal from upper left to down right on each scale level.
I checked the following things:
1) Use of floating point precision (16-bit and 32-bit). No change!
2) Use of own fragment shader (bilinear-, barlett-, gauss-filtering). No change!
3) The data initially written down are precise at all. These effects are appearing after the first scaling.
I cannot use mipmaps since i want to control the build procedure. Do anyone know how this effect can be avoided?
Thank's in advance
Stefan
