On Fri, Sep 10, 2010 at 10:04 AM, Chris Wood <[email protected]> wrote:
> I take it you've considered depth sorting? Should be fixable with a bit of > javascript (order by z, then resize and set z=0) but overlapping sprites > will really spoil the illusion ;) (Another option is to do z *= 0.000001 so > the depth is not visible, but they'll still be sorted correctly). > > Chris > Thanks for the thought on that Chris - in my "guesstimate" setups that aspect really became apparent, so the particular illusions just place objects side by side when things are "2D". -George > > > On 10 September 2010 14:59, George Toledo <[email protected]> wrote: > >> >> >> On Fri, Sep 10, 2010 at 9:57 AM, vade <[email protected]> wrote: >> >>> Actually, with all due respect you did not pay attention. I believe Chris >>> answered it for you. Get the modelview and projection matrix and do some >>> math. >>> >>> >> I wasn't referring to Chris's reply, where he states that the projection >> matrix is undocumented. >> >> -George >> >> >>> >>> On Sep 10, 2010, at 8:47 AM, George Toledo wrote: >>> >>> With all due respect, you're answering a question I'm not asking, and Dr. >>> Wright was answering a question by guessing. >>> >>> On Sep 10, 2010 4:57 AM, "Louis Schultz" <[email protected]> wrote: >>> > George, >>> > >>> > Dr Wright was sending you in the correct direction. Perspective assumes >>> a fixed distance from a fixed eye point to a fixed picture plane. The view >>> that eye has is perpendicular to the picture plane, and an object to be >>> represented on that picture plan is some distance behind that plane. >>> > >>> > The apparent effect of moving an object away is a function of its >>> distance from the eye AND the distance from the eye to the front of the >>> picture plane. Perhaps the attached image will help to make that more clear. >>> > >>> > >>> > If we let DP = distance from eye to picture plane; DO = distance from >>> eye to the object, then a plane or line parallel to the picture plane would >>> appear to be (DE/DO) x (absolute size of the line or plane) >>> > >>> > You can also use that same formula and a bit of trigonometry to figure >>> out how to make a plane or line appear to tilt in relation to the picture >>> plane. In the attached image, imagine the hypotenuse of the blue 45 deg. >>> right triangle as an edge view of a 1 unit square (that square being >>> perpendicular to the diagram plane). If the edge at A were projected onto a >>> picture plane 2 units from the eye position, then it would measure 2/3 = >>> 0.667 units. If the line at B were project to the same plane, it would >>> measure 2/(3+sqrt0.5) = 0.54 units. >>> > >>> > To make it clear where those numbers come from, The hypotenuse is 1 >>> unit, and the square root of 0.5 is the hypotenuse length x cosine 45, which >>> is the angle of the plane in relation to the perpendicular view of the eye. >>> > >>> > In that case, two edges remain parallel to the picture plane, but with >>> a little work you can figure out how to make a plane appear at any distance >>> and at any angle to the picture plane. If it gets confusing, all you should >>> really need get it figured out are some quick sketches of top and side views >>> (picture plane appears as a line). >>> > >>> > One final note, perspective is a useful tool, but not a true depiction >>> of reality (whatever that is). The further an object in that system moves >>> from the line of the view, the more distortion creeps in. Consider a 1 unit >>> square 8 units behind the picture plane and parallel to it. The square is >>> centered on the line of view. The picture plane is 2 units from the view >>> point. That square would be 10 units from the eye. If it were moved it 10 >>> units away from the line of view in the same plane it would actually then be >>> 14 units from the eye point. It would project the same size though based on >>> our formula. That contradicts what we know to happen. >>> > >>> > We actually see in something more like spheres of vision rather than >>> planes. The distance between the eye and the picture plane has to be zero >>> for that to really work though, which is, to state the obvious, how you do >>> see the world. >>> > >>> > I mention that both as a warning to keep things somewhat centered if >>> you don't want them to look weird, but also as an encouragement to play with >>> the notion of curved picture "planes" if it strikes your fancy. The artists >>> Victor Vasarely and of course Escher might be inspirational for that. >>> > >>> > >>> > >>> > >>> > >>> > >>> > On Sep 9, 2010, at 8:38 PM, George Toledo wrote: >>> > >>> >> So, just so I know where this is at, the statement that there is no >>> way to do this 100% accurately in QC is valid? >>> >> >>> >> -George Toledo >>> >> >>> >> On Thu, Sep 9, 2010 at 2:05 PM, Christopher Wright < >>> [email protected]> wrote: >>> >>> I basically want to know the exact number, from Apple (or really, >>> from anyone, but not a visual comparison/kinda close thing, like this). >>> >> >>> >> >>> >> There isn't an exact number -- this sort of thing requires passing the >>> coordinates through the projection matrix QC uses (undocumented, but it's >>> been investigated on the list before in the past) as well as the model view >>> matrix (which can be arbitrarily configured via Trackball and 3D >>> Transformation). >>> >> >>> >> i'm going to assume this is for faking Z on a Billboard? If so, why >>> not just use a sprite? If not, what other reason is there to fake Z >>> positioning like this? (I'm not saying there isn't a reason, I'm just not >>> able to think of one off the top of my head :). >>> >> >>> >> -- >>> >> Christopher Wright >>> >> [email protected] >>> >> >>> >> >>> >> >>> >> >>> >> _______________________________________________ >>> >> Do not post admin requests to the list. They will be ignored. >>> >> Quartzcomposer-dev mailing list ([email protected]) >>> >> Help/Unsubscribe/Update your Subscription: >>> >> >>> http://lists.apple.com/mailman/options/quartzcomposer-dev/lulu%40vt.edu >>> >> >>> >> This email sent to [email protected] >>> > >>> _______________________________________________ >>> Do not post admin requests to the list. 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