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Don't get transformation when doing x axis
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Posts: 2


Wed, Mar 6 2013

Hi, I have a group with two meshes.

the first is located at 0,0,0
the second at 0.2, 0.2, 0

When I rotate in z, or y, and I retrieve the matrix (with the model view transformations) using the matrix property of NGLMesh, I can see the transformations occurring in the matrix cos(angle) -sin(angle) etc. As it is expected for OpenGL.

However, when I retrieve the matrix after doing x rotation. Nothing changes. I guess it is doing the calculation since on screen it actually works. But the property doesn't change in the mesh object.

How can this be fixed?

Thank you very much.

-(void)loadMeshes{//I call this in viewDidAppear
NSDictionary *settings = [NSDictionary dictionaryWithObjectsAndKeys:
//kNGLMeshOriginalYes, kNGLMeshKeyOriginal,
kNGLMeshCentralizeYes, kNGLMeshKeyCentralize,
@"0.3", kNGLMeshKeyNormalize,

_group = [[NGLGroup3D alloc]init];

_meshA = [[NGLMesh alloc] initWithFile:@"untitled.obj" settings:settings delegate:nil];
NGLMaterial *material = [[[NGLMaterial alloc]init]autorelease];
material.diffuseColor = nglColorMake(0.8, 0.8, 0.2, 1);
_meshA.material = material;
_meshA.scaleX = 0.2;
_meshA.scaleY = 0.2;
_meshA.scaleZ = 0.2;
_meshA.x = 0;
_meshA.y = 0;
_meshA.z = 0;
[_group addObject:_meshA];

_camera = [[NGLCamera alloc] initWithMeshes:_meshA, nil];

_meshB = [[NGLMesh alloc] initWithFile:@"untitled.obj" settings:settings delegate:nil];

_meshB.material = material;
_meshB.scaleX = 0.2;
_meshB.scaleY = 0.2;
_meshB.scaleZ = 0.2;
_meshB.x = 0;
_meshB.y = 0;
_meshB.z = 0;
[_group addObject:_meshA];

UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTap:)];
[self.view addGestureRecognizer:tapRecognizer];
[_group removeObject:_mesh];
_group.rotationSpace = NGLRotationSpaceWorld;
[_camera translateToX:0 toY:0 toZ:1];
_camera.lookAtTarget = _group;
//I do either of the following, only one of them, the other 2 I comment them out
_group.rotateX = 45;//
_group.rotateY = 45;//
_group.rotateZ = 45;//

//Now I analyze how the matrix is changed
for (int y = 0 ; y<4 ; y ) {
NSLog(@"MV [%f][%f][%f][%f]", _group.matrix[y][0], _group.matrix[y][1], _group.matrix[y][2], mesh.matrix[y][3]);
//As I say above, I can see the predicted changes when I rotate over Y or Z, but not X. The rotation occurs in the screen, so the OpenGL engine is definetively doing the work.
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Posts: 2


Wed, Mar 6 2013

In response to: @RaulCatena

Apologies, for _meshB

_meshB.scaleX = 0.2;
_meshB.scaleY = 0.2;
_meshB.scaleZ = 0.2;
_meshB.x = 0.2;
_meshB.y = 0.2;
_meshB.z = 0;
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Posts: 571


Sun, Nov 24 2013

In response to: @RaulCatena

Hello buddy,

There are many concepts involved in this simple snippet of code.
But your initial thought is completely right. If you make a change in the X rotation using the absolute mode (not relatively), then you should see your change by retrieving the matrix property (which is the model view only).

This is happening, but if in your project you don't see it, please send us your project for investigation via email. We'll check it.
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