Allegro.cc - Online Community

Allegro.cc Forums » Programming Questions » al_draw_rotated_bitmap() giving distorted edges

Credits go to Edgar Reynaldo for helping out!
This thread is locked; no one can reply to it. rss feed Print
 1   2 
al_draw_rotated_bitmap() giving distorted edges
Audric
Member #907
January 2001

Note that your sprite has antialiasing. I'm not speaking of the borders (alpha on the fringe), but on the surface of the image, some pixel colors are drawn a spcific color in order to smooth the difference between pixels around it : for example a pixel can be set grey because it's between a black shape and a white shape. If such image is rotated at a similar zoom level to the original (*), the grey pixel may be preserved, and end up in a place which is not between a black and a white pixel, so it looks out of place.
This is a very simplified explanation (the rotozoom doesn't just juggle pixels), but the effect is real and can explain some oddities that appear at several angles but always at same position relative to sprite (ie. "right elbow", "corner of backpack"...)

(*) Scaling UP the sprite amplifies the problem, scaling it down makes it disappear very quickly.

Thinkal VB
Member #16,859
May 2018

Thank you, Audric for the replay
I never noticed that changes ...... Now I know; I will try to use good quality High definition images and will scale it down when I need to draw - Hope that fix the problem for now. My project is live and if you like to take a peek into the stuff i am doing or need to edit or suggest changes feel free to do so.
https://github.com/ThinkalVB/NearEarth
Thank you once again for the help...

NiteHackr
Member #2,229
April 2002

For my Deluxe Pacman 2 game, I rotate the Pacman character, as the main image just faces the right. For my setup, all I really have is:

al_set_new_bitmap_flags(ALLEGRO_MAG_LINEAR);

I have a bunch of code commented out that I tried in the past, but this seems to be the one I ended up using that works well using DirectX and OpenGL.

Not sure if that would help or not, been a while since I worked on this sort of problem. And in my game the rotations are increments of 90 degrees.

Thinkal VB
Member #16,859
May 2018

Thank you Neil Roy,
I am trying a combination of MIP_MAP and MIN_LINEAR , I am more into zooming out, not much zooming in, but I have backed up all of your suggestions for future references if a need arise. Thank you once again for leaving your valuable comments in here.

relpatseht
Member #5,034
September 2004
avatar

Not relevant, but something you should know: the only minification filter you should ever use is some sort of mip mapping. Anything else will cause you to thrash the texture cache.

Thinkal VB
Member #16,859
May 2018

Thank you relpatseht,
:) Almost forgot that fact.

 1   2 


Go to: