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How do I apply a perspective transform to a UIView?
How to change the perspective, 3D Transform, skew ,distortion, rotation of the image view? Any sample projects for this.Thanks in Advance
3D transforms, rotations, skews, etc are usually done with CATransform3D.
As per the documentation (Core Animation Programming Guide):
The CATransform3D data structure defines a homogenous
three-dimensional transform (a 4 by 4 matrix of CGFloat values) that
is used to rotate, scale, offset, skew, and apply perspective
transformations to a layer.
As an example, to do a 3D rotation towards the bottom right, you would do something like:
myImageView.layer.transform = CATransform3DRotate(CATransform3DIdentity, 1.75, 0.85, 0, 0);
and don't forget to
#import <QuartzCore/QuartzCore.h>
A fantastic sample project is Mark Pospesel's Enter the Matrix. The code is on GitHub, also check out the explanatory slides.
Related
I am stuck in my application feature. I want cropping feature similar to Cam Scanner Cropping.
The screens of CAM-SCANNER are:
I have created similar crop view.
I have obtained CGPoint of four corners.
But How can I obtained cropped image in slant.
Please provide me some suggestions if possible.
This is a perspective transform problem. In this case they are plotting a 3D projection in a 2D plane.
As, the first image has selection corners in quadrilateral shape and when you transform it in a rectangular shape, then you will either need to add more pixel information(interpolation) or remove some pixels.
So now actual problem is to add additional pixel information to cropped image and project it to generate second image. It can be implemented in various ways:
<> you can implement it by your own by applying perspective tranformation matrix with interpolation.
<> you can use OpenGL .
<> you can use OpenCV.
.. and there are many more ways to implement it.
I had solved this problem using OpenCV. Following functions in OpenCV will help you to achieve this.
cvPerspectiveTransform
cvWarpPerspective
First function will calculate transformation matrix using source and destination projection coordinates. In your case src array will have values from CGPoint for all the corners. And dest will have rectangular projection points for example {(0,0)(200,0)(200,150)(0,150)}.
Once you get transformation matrix you will need to pass it to second function. you can visit this thread.
There may be few other alternatives to OpenCV library, but it has good collection of image processing algorithms.
iOS application with opencv library is available at eosgarden.
I see 2 possibilities. The first is to calculate a transformation matrix that slants the image, and installing it in the CATransform3D property of your view's layer.
That would be simple, assuming you knew how to form the transformation matrix that did the stretching. I've never learned how to construct transformation matrixes that stretch or skew images, so I can't be of any help. I'd suggest googling transformation matrixes and stretching/skewing.
The other way would be to turn the part of the image you are cropping into an OpenGL texture and map the texture onto your output. The actual texture drawing part of that would be easy, but there are about 1000 kilos of OpenGL setup to do, and a whole lot to learning in order to get anything done at all. If you want to pursue that route, I'd suggest searching for simple 2D texture examples using the new iOS 5 GLKit.
Using the code given in Link : http://www.hive05.com/2008/11/crop-an-image-using-the-iphone-sdk/
Instead of using CGRect and CGContextClipToRect Try using CGContextEOClip OR CGContextClosePath
Though i havnt tried this... But i have tried drawing closed path using CGContextClosePath on TouchesBegan and TouchesMoved and TouchesEnd events.
Hope this can give more insight to your problem...
I am stuck in my application feature. I want cropping feature similar to Cam Scanner Cropping.
The screens of CAM-SCANNER are:
I have created similar crop view.
I have obtained CGPoint of four corners.
But How can I obtained cropped image in slant.
Please provide me some suggestions if possible.
This is a perspective transform problem. In this case they are plotting a 3D projection in a 2D plane.
As, the first image has selection corners in quadrilateral shape and when you transform it in a rectangular shape, then you will either need to add more pixel information(interpolation) or remove some pixels.
So now actual problem is to add additional pixel information to cropped image and project it to generate second image. It can be implemented in various ways:
<> you can implement it by your own by applying perspective tranformation matrix with interpolation.
<> you can use OpenGL .
<> you can use OpenCV.
.. and there are many more ways to implement it.
I had solved this problem using OpenCV. Following functions in OpenCV will help you to achieve this.
cvPerspectiveTransform
cvWarpPerspective
First function will calculate transformation matrix using source and destination projection coordinates. In your case src array will have values from CGPoint for all the corners. And dest will have rectangular projection points for example {(0,0)(200,0)(200,150)(0,150)}.
Once you get transformation matrix you will need to pass it to second function. you can visit this thread.
There may be few other alternatives to OpenCV library, but it has good collection of image processing algorithms.
iOS application with opencv library is available at eosgarden.
I see 2 possibilities. The first is to calculate a transformation matrix that slants the image, and installing it in the CATransform3D property of your view's layer.
That would be simple, assuming you knew how to form the transformation matrix that did the stretching. I've never learned how to construct transformation matrixes that stretch or skew images, so I can't be of any help. I'd suggest googling transformation matrixes and stretching/skewing.
The other way would be to turn the part of the image you are cropping into an OpenGL texture and map the texture onto your output. The actual texture drawing part of that would be easy, but there are about 1000 kilos of OpenGL setup to do, and a whole lot to learning in order to get anything done at all. If you want to pursue that route, I'd suggest searching for simple 2D texture examples using the new iOS 5 GLKit.
Using the code given in Link : http://www.hive05.com/2008/11/crop-an-image-using-the-iphone-sdk/
Instead of using CGRect and CGContextClipToRect Try using CGContextEOClip OR CGContextClosePath
Though i havnt tried this... But i have tried drawing closed path using CGContextClosePath on TouchesBegan and TouchesMoved and TouchesEnd events.
Hope this can give more insight to your problem...
I have been trying to develop a 3D game for a long time now. I went through
this
tutorial and found that I didn't know enough to actually make the game.
I am currently trying trying to add a texture to the icosahedron (in the "Look at Basic Drawing" section) he used in the tutorial, but I cannot get the texture on more than one side. The other sides are completely invisible for no logical reason (they showed up perfectly until I added the texture).
Here are my main questions:
How do I make the texture show up properly without using a million vertices and colors to mimic the results?
How can I move the object based on a variable that I can set in other functions?
Try to think of your icosahedron as a low poly sphere. I suppose Lamarche's icosahedron has it's center at 0,0,0. Look at this tutorial, it is written for directX but it explains the general principle of sphere texture mapping http://www.mvps.org/directx/articles/spheremap.htm. I used it in my project and it works great. You move the 3D object by applying various transformation matrices. You should have something like this
glPushMatrix();
glTranslatef();
draw icosahedron;
glPopMatrix();
Here is my code snippet of how I did texCoords for a semisphere shape, based on the tutorial mentioned above
GLfloat *ellipsoidTexCrds;
Vector3D *ellipsoidNorms;
int numVerts = *numEllipsoidVerticesHandle;
ellipsoidTexCrds = calloc(numVerts * 2, sizeof(GLfloat));
ellipsoidNorms = *ellipsoidNormalsHandle;
for(int i = 0, j = 0; i < numVerts * 2; i+=2, j++)
{
ellipsoidTexCrds[i] = asin(ellipsoidNorms[j].x)/M_PI + 0.5;
ellipsoidTexCrds[i+1] = asin(ellipsoidNorms[j].y)/M_PI + 0.5;
}
I wrote this about a year and a half ago, but I can remember that I calculated my vertex normals as being equal to normalized vertices. That is possible because when you have a spherical shape centered at (0,0,0), then vertices basically describe rays from the center of the sphere. Normalize them, and you got yourself vertex normals.
And by the way if you're planning to use a 3D engine on the iPhone, use Ogre3D, it's really fast.
hope this helps :)
I've been creating iPhone apps for a while now, using basic transformations (rotations, scale, etc) but now I'd like to do something a little more complex.
Maths really isn't my strongest point... but I was wondering how I might go about adding 'perspective' to a UIView (see the image below). I quickly mocked the screenshot up using skew options in Photoshop.
I have had a look around stackoverflow for solutions to this, I found How do I apply a perspective transform to a UIView? which works excellently - but it's not really what i'm after because the height of the left most edge is larger than the right most edge.
Does anyone know how I might go about doing this CATransform3D but without these differing heights?
alt text http://img594.imageshack.us/img594/4354/perspectivel.png
If you just want to skew, you don't need 3D transform. An affine transform will suffice.
-(void)drawRect:(CGRect)rect {
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGAffineTransform transform = CGAffineTransformIdentity;
transform.b = -0.1;
transform.a = 0.9;
CGContextConcatCTM(ctx,transform);
// do drawing on the context
}
this is a modified copy&paste from a project which has a similar transform, but you may need to tune the parameters a and b. This will give a 1 in 9 rise from left to right (0.1/0.9), while condensing from left to right to 90% (0.9).
I recently started working with OpenGL ES for the iPhone, and I am having a bit of trouble with it. I want to be able to rotate an object with your fingers. My problem is that I have my object placed at (0, 0, -3), and I would like to rotate it about its center. I know that I need to translate back to the origin, rotate, and then bring it back to the original place. I think I am facing a problem because I am using a matrix to keep track (?) of all of my rotations/translation/scaling etc, and I think it may be combining the operations in a way that order is not even considered (so the two translations would cancel each other). I just started learning OpenGL a day ago and am a complete newbie, so my assumption may be wrong.
Here is the part of the in drawView that I am having trouble with:
GLfloat matrix[16];
glGetFloatv(GL_MODELVIEW_MATRIX, matrix);
glLoadIdentity();
glTranslatef(0, 0, 3); // bring to origin
glRotatef(self.angle, self.dy, self.dx, 0); // rotate
glTranslatef(0, 0, -3); // put it back in place
glMultMatrixf(matrix); // save the transformations performed
Help would be much appreciated, thank you!
Retrieving the modelview matrix, and then multiplying it back on after your rotation seems fishy, but it depends on what your other transforms are and what coordinate space things are supposed to be. Your comment on the glMultMatrix line doesn't correspond with what you're doing.
Normally you would just do the translate+rotate+translate as the most local actions on the object, just before you render it. Also note that this would only apply if you're object is at (0, 0, -3) in object-space. If it's at that location in world space, then the rotation will already rotate the object around its own center if you have previously made a series of transform calls (translate, rotate, etc) to move the object to its intended position in the world.
Transform order is one of the tricky parts of learning OpenGL. As a general rule of thumb, your operations start with the outer-most and progress to the inner-most. So a typical simple set of transforms would be: the inverse of the camera transform to move the world to match up with the camera, then the object's translation to move it to its world-space position, then the rotation to set it's intended orientation. The PushMatrix/PopMatrix stack functions let you save and undo part of that series of transforms so that groups of objects can share portions of that chain.