On Apr 11, 7:42 am, "Alex Holkner" <[EMAIL PROTECTED]> wrote:
> On 4/11/08, Richard Jones <[EMAIL PROTECTED]> wrote:
> > On Fri, 11 Apr 2008, Michael Halle wrote:
> > > In looking through the sprite code, I saw that computed vertices get
> > > rounded off to ints, and then passed in integer form to OpenGL. This
> > > process happens even when the sprite is scaled and rotated, where
> > > vertices would in general not fall on pixel boundaries.
>
> > > Seems like for small sprites, noticeable distortion or bad packing could
> > > happen.
>
> > So this is something you've not actually observed?
I've observed this when rotating a pyglet.Sprite.
This code demonstrates the problem. The image on the left seems to
pulse in and out.
import pyglet
from pyglet.gl import *
from itertools import *
window = pyglet.window.Window()
image = pyglet.resource.image('simon.jpg')
image.anchor_x, image.anchor_y = image.width*0.5, image.height*0.5
sprite = pyglet.sprite.Sprite(image, x=100, y=100)
def update(T):
sprite.rotation += 1.0
pyglet.clock.schedule_interval(update, 1.0/30)
x,y = image.anchor_x, image.anchor_y
vertices = (-x, -y, 0), (-x, +y, 0), (+x, +y, 0), (+x, -y, 0)
texcoords = [i for i in izip(*[chain(image.texture.tex_coords, )]*3)]
@window.event
def on_draw():
window.clear()
glLoadIdentity()
sprite.draw()
glLoadIdentity()
glTranslatef(200,100,0)
glRotatef(sprite.rotation, 0, 0, 1)
glEnable(image.texture.target)
glBindTexture(image.texture.target, image.texture.id)
glBegin(GL_QUADS)
for v, t in izip(vertices, texcoords):
glTexCoord3f(*t)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
glVertex3f(*v)
glEnd()
pyglet.app.run()
>
> > > As far as I know, graphics cards usually use floats internally anyway --
> > > are there real performance hits in removing the rounding and just
> > > passing the floats down to OpenGL?
>
> > The rounding is not done for performance.
>
> > More often than not you'll get artifacts and fuzziness on raster graphics
> > if
> > they're not pixel-aligned. The most common artifact is flickering border
> > where pixels bleed in from adjacent images (in the same texture).
>
> Even without adjacent images, you'll get this flicker as any high
> frequency parts of the texture (lines, for example) pass in and out of
> pixel alignment.
I've got a hunch (I could be wrong) that this problem can be mitigated
by using a filter on the textures. Something like:
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
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