ios - Why does a CALayer's transform3D's m34 need to be modified before applying the rotate transform? -

-

the following code can make perspective rotation transform layer:

catransform3d transform3dfoo = catransform3didentity;  transform3dfoo.m34 = -1.0 / 1000;  transform3dfoo = catransform3drotate(transform3dfoo, m_pi / 4, 1, 0, 0);

however, if 2 lines reversed:

catransform3d transform3dfoo = catransform3didentity;  transform3dfoo = catransform3drotate(transform3dfoo, m_pi / 4, 1, 0, 0);  transform3dfoo.m34 = -1.0 / 1000;

then perspective gone. orthographic (no perspective). familiar perspective know why reason?

update:

// first identity , transform3dfoo.m34 = -1.0 / 1000; done  1.00000     0.00000     0.00000     0.00000  0.00000     1.00000     0.00000     0.00000  0.00000     0.00000     1.00000    -0.00100  0.00000     0.00000     0.00000     1.00000   // , catransform3drotate(transform3dfoo, m_pi / 4, 1, 0, 0);  1.00000     0.00000     0.00000     0.00000  0.00000     0.70711     0.70711    -0.00071  0.00000    -0.70711     0.70711    -0.00071  0.00000     0.00000     0.00000     1.00000   // start identity , rotate statement done:  1.00000     0.00000     0.00000     0.00000  0.00000     0.70711     0.70711     0.00000  0.00000    -0.70711     0.70711     0.00000  0.00000     0.00000     0.00000     1.00000   // , transform3dfoo.m34 = -1.0 / 1000; done  1.00000     0.00000     0.00000     0.00000  0.00000     0.70711     0.70711     0.00000  0.00000    -0.70711     0.70711    -0.00100  0.00000     0.00000     0.00000     1.00000

(the tag of "opengl" added because same principle in opengl)

setting m34 first equivalent rotating first , projecting. setting m34 last equivalent projecting first , rotating. input coordinates have z=0, projecting first won't anything.

to see why is, need understand little how transform matrices work.

i believe in ca positions transformed transform matrix m doing:

[x y z w] = [x y z w] * m

(see http://en.wikipedia.org/wiki/matrix_multiplication)

multiplying 2 transform matrices equivalent concatenating transforms. transform/matrix on left happens first. it's pretty easy see why is:

[x y z w] * (left * right) = ([x y z w] * left) * right

most (all?) of ca transform functions (eg catransform3drotate) premultiply transform matrix aptly constructed matrix, eg:

m = rotate * m

setting m34 equivalent premultiplying projection matrix, is:

m = proj * m

(where proj projection matrix -- identity matrix m34 set)

this isn't entirely true (which why keep saying roughly) -- works if m has 0s , 1s in right places. basically, in general case, setting m34 nonsense thing -- right thing multiply projection matrix.

anyway, if put should able see why said in first paragraph true (assuming haven't made mistakes :)


Comments

Post a Comment

Popular posts from this blog

django - How can I change user group without delete record -

-
on website user have 1 group. , user can change group. it's made user.groups.clear() and user.groups.add(new_group) but it's not efficient, because there 2 sql query: delete, insert. how can change group update query? user , group related each other using manytomanyfield . means intersection table exists relating both entities, , if don't specify model map (using through attribute) django creates 1 you. looking @ sources django.contrib.auth.models see that's case. fortunatly, can access intermediary model using through attribute of manager (in case, user.groups.through ). can use regular model. example: >>> alice = user.objects.create_user('alice', 'alice@example.com', 'alicepw') >>> employee = group.objects.create(name='employee') >>> manager = group.objects.create(name='manager') >>> alice.groups.add(employee) >>> alice.groups.all() [<group: employee...
Read more

java - Need to add SOAP security token -

-
i need set custom soap header attribute on jax-ws generated webservice client. case webservice calls must go through proxy server requiring specific token (recieved web request header) present in soap request header. e.g.: 1 carserviceservice service = null; 2 service = new carserviceservice(new url(url), new qname(qname); 3 carserviceendpoint port = service.getcarserviceport(); it seems in line 3 wsdl retrieved , call fails due missing security token. 1 point direction on how done? a detailed example has been mentioned here: creating , deploying jax-ws web service on tomcat 6 this article shows how create , use security token .
Read more

java - EclipseLink JPA Object is not a known entity type -

-
i have strange problem eclipselink , object want persist. have 1 object (keypointlistimpl) stores object keypointimpl in list. persisting keypointimpl objects works great if try persist keypointlistimpl object java.lang.illegalargumentexception says object keypointimpl isn't known entity type. here keypointimpl code: @entity @table(name="keypoints") public class keypointimpl implements keypoint { @id @generatedvalue(strategy = generationtype.identity) private int id; @enumerated(enumtype.string) private detectortype keypointtype; private float x; private float y; private float size; private float angle; private float response; private int octave; private int classid; ... } here keypointlistimpl code: @entity @table(name="keypointlists") public class keypointlistimpl implements keypointlist { @id @generatedvalue(strategy = generationtype.identity) private int id; @onetoone(cascade={ca...
Read more