A Texture2D is mapped on a sphere. Thanks to GetPixel(raycastHit.texturecoord) I can get the pixel value of this texture, when, for instance, a ray hit the sphere. So if I convert an image I to a texture T and map T on a GameObject G, I can get the pixel value from G to I (G--textureCoord-->T--GetPixel-->I). If I convert those (x,y) coordinates into world coordinates, I can trigger event on certain colors, so it works. I use this solution to perform pixel to world position.
But I can't do the opposite. Imagine that I have a list of bounding boxes for different objects on the image I (so with coordinates between I.width and I.height). If I convert those coordinates (bx1, bx2) into world coordinates it simply doesn't work.
I noticed that when I compare the GetPixel value when I target a given color on G with my controller, I don't get the same pixel coordinates as the one on the original image.
In the end I want to get the texture coordinate from an image (G<--textureCoord_to_word_coordinates--T<--?????---I).
Related
I want to create a shader that uses different coordinates for light calculations than for what's being displayed. This probably sounds strange, but I would like to do this for lighting a top-down 2D game.
I want to write a vertex shader that offsets the Z coordinate by the value of the Y coordinate for display, but uses unmodified coordinates for lighting calculation.
Is this possible to do, and if so, where would I start?
So far I have a surface shader that offsets the Z coordinate by the value of the Y coordinate, but unity is using the modified coordinates to calculate lighting, I would like unity to use the unmodified coordinates for light calculations.
I want to create a shader that will grab a pixel color by the object position
Basically Texture2D.GetPixel(transform.position.x,transform.position.z), but in shader.
You need a SampleTexture2D node to get pixel color in texture, Use Position Node as a sample uv, the Position will give a 3d vector, you can use Split node and Combine node to extract the axis you want and recombine them, then connect it to the UV socket on SampleTexture2D node.
I used the "imfreehand" to crop an irregular shape and save its positions into a variable. This position variable is a 85*2 double matrix (85 points, X and Y coordinates). Now, I want to use the same position to crop another image (different layer of the image, but the location of the objects is the same). The functions I can find all requires rectangle positions (X1,X2,Y1,Y2). In my situation, I have 82 different (X,Y) coordinates, how can I use the position information to crop a new image?
From what I understand, you want to take the coordinates created by imfreehand(...) to create a cropable object on another image. You can use the function impoly(hparent,position) for this purpose.
The MathWorks page provides an example to guide you on its usage.
I have a 3D matrix of data in matlab, but I want to extract an arbitrarily rotated slice of data from that matrix and store it as a 2D matrix, which I can access. Similar to how the slice() function displays data sliced at any angle, except I would also like to be able to view and modify the data as if it were an array.
I have the coordinates of the pivot-point of the plane as well as the angles of rotation (in x, y and z axis), I have also calculated the equation of the plane in the form:
Ax + By + Cz = D
and can extract a 3D matrix containing only the data that fall on that plane, but I don't know how to then convert that into a simple 2D array.
Another way of doing it would be to somehow rotate the source matrix in the opposite direction of the angle of the plane, so as to line up the plane of data with the XY axis, and simply extract that portion of the matrix, but I do not know if rotating a matrix like that is possible.
I hope this hasn't been answered elsewhere, I've been googling it all day, but none of the problems seem to exactly match mine.
Thanks
You can take a look at the code here. I think the function is similar to what you are trying to solve.
The function extracts an arbitrary plane from a volume given the size of the plane, the center point of the plane, and the plane normal, i.e. [A,B,C]. It also outputs the volumetric index and coordinate of each pixel on the plane.
Aha! May have just solved it myself.
To produce the plane equation I rotate a normal vector of (0,0,1) using rotation matrices and then find D. If I also rotate the following vectors:
(1,0,0) //step in the x direction of our 2D array
and
(0,1,0) //step in the y direction of our 2D array
I'll have the gradients that denote how much my coordinates in x,y,z have to change before I step to the next column in my array, or to the next row.
I'll mock this up ASAP and mark it as the answer if it works
EDIT: Ok slight alteration, when I'm rotating my vectors I should also rotate the point in 3D space that represents the xyz coordinates of x=0,y=0,z=0 (although I'm rotating around the centre of the structure, so it's actually -sizex/2,-sizey/2,-sizez/2, where size is the size of the data, and then I simply add size/2 to each coordinate after the rotations to translate it back to where it should be).
Now that I have the gradient change in 3D as I increase the x coordinate of my 2D array and the gradient change as I increase the y coordinate, I can simply loop through all possible x and y coordinates (the resulting array will be 50x50 for a 50x50x50 array, I'm not sure what it will be for irregular sizes, which I'll need to work out eventually) in my 2D array and calculate the resulting 3D coordinates on my plane in the data. My rotated corner value serves as the starting point. Hooray!
Just got to work out a good test for this encompassing all angles and then I'll approve this as an answer
For openGl expample, Xcode given a project GlGravity. But Instead of showing yellow color how to apply a Texture image without textureCoordinates?.
You need some kind of texture coordinate, otherwise the whole concept of textures makes no sense: A texture is a function mapping a set of n coordinates to some value (depth, luminance, alpha, colour or combination of those) defined by data the samples are taken from and interpolated.
You can generate the texture coordinates, either statically from your mesh, or in the vertex shader. Or you supply them directly. But you need some texture coordinates to make this work. A very cheap and simple texture coordinate generator is using the vertex position as texture coordinate; this will project your texture along the coordinates axes onto the model. So if you've got a 2D texture it will be applied in the XY plane, as if there were a parallel projecting slide projector at coordinates (0,0,\infinity).