I am not sure how to put this problem in a single sentence, sorry if the title is misleading.
I am currently developing a simple terrain editor with a circle-shaped brush size. The image below shows a few cases that represent my problem.
additional info: the square size is fixed and uniform and in the current version, my concern is only to find which one is hit and which one is not (the amount of region covered is important for weighting the hit, but probably not right now)
My current solution (which is not even correct for a certain condition) is: given a hit in a position (x, y) with radius r, loop through all square from (x-radius, y-radius) to (x+radius, y+radius) and apply 2-D box to circle collision detection. But I don't think this is optimal (or even correct IMO).
Can anyone help me with this one? Thank you
Since i can't add a simple comment due to bureaucracy on this website i have to type it out here.
Anyway you're in luck since i was trying to do this recently as well! The way i did it is i iterated through the vertex array and check if the current vertex falls inside the radius of the circle. But perhaps what you want is to check it against each quad center and if that center falls inside the radius then add the whole quad as it's being collided.
Of course depending on the size of your grid the performance will vary so it's good to try to iterate through as few quads as needed. Though accessing these quads from the array is something you have to figure out yourself.
https://www.youtube.com/watch?v=UQINoSwvmto
My goal is to rotate the object just like how it's done in Photoshop (video above)
I can't seem to figure out how to do it. I've tried several solutions i saw here but none worked. they either used the objects up vector to "look at" or just used one axis instead of calculating the angle between the first touch and the latest touch. There lies my second problem, when I tried that solution sometimes the angles would come out janky and the object would spin weirdly
Heyho. I just came up with a tricky question.
I did something like this: http://jsfiddle.net/LspdF/1/
As you cann see there are more than 4 sites. Thats why I did the following:
Whenevery the pic-numer is greater than the last pic-number I turn the cube left, otherwise rigt. Thats why it can happen, that the css is somewhat like this:
transform: rotateY(450deg)
Since a circle only has 360 deg it turns and turns but always in the right direction.
Now I wanted to add a nice effect. Something like this: http://jsfiddle.net/p8a2t/
For this effect I need the 14th value of the 3d matrix created by the browser (z-value of translation). Since this value is poorly not the same as translateZ(), I have to use the matrix3d()-attribute.
Thats why I calculate the rotateY myself. But as you know the sin and cos are periodic and wont work with my 450deg. They reset the cube to 90deg which makes the cube spin back very fast.
My Question: How to denie that? Is there any possibility to change the matrix for spinning more than 360deg?
PS: The effect is realized using transition. There may be code in the fiddles which isnt used since I had to create both examples at once.
PPS: Sometimes the calculation has fatal numeric errors (near zero but not rly zero). I tried to avoid that using toFixed but for some reason that wont work sometimes. Same with Math.round. Note that you can break the second example clicking many links while the animation is still not done. But thats no point here :)
Any help is appreciated!
i am playing around with the rotationX/Y/Z properties available in flashplayer since version 10. for testing purpose i created a cube and put canvas objects on three sides of it (top, front, bottom) and created a tween to get the values required for turing by 90 deg. turning the cube (a canvas) using rotationX = xx works well when the three side-canvas objects are small and filled with a not-to-complex element hierarchy. when using larger and more complex content it slows down. the next idea was to remove the canvas elements content and replace it by a snapshotimage of the content instead before starting the turn, after the turn is performed the original content is put back on the sides again. this results in a good perfomance increase. using a tween the last step of rotation is done in the function that is called as the tweenEnd handler. in this function also the process of copying the canvases content back is performed. unfortunately this results in a short hang of the cube right in that last rotation step, the reason for which is that rotation and copying back takes place at the same time.
so i could wait for some time after having called cube.rotationX = endValue by using a timer or setTimeout(func, 500), but this is ugly.
so my question is: after having called cube.rotationX = endValue a period of time is required to calculate data for the rotation and do the rotation itself. is there a way to find out the point in time when the rotation has ended, so that then the copying can be started ?
thank you in advance
tyler
There's no any default event, dispatching when rotation is completed. But I think of using callLater() function to copy back content. Try it.
that is exactly the point, there is not an event indicating the end of the rotation. the solution using callLater() instead of using setTimeout() appears to be an improvement however since waiting for a certain amount of time is always invloving some 'hope it works on machine x'. thank you very much for the hint !
greetings
tyler
I'm doing some image processing, and I need to find some information on line growing algorithms - not sure if I'm using the right terminology here, so please call me out on this is needs be.
Imagine my input image is simply a circle on a black background. I'd basically like extract the coordinates, so that I may draw this circle elsewhere based on the coordinates.
Note: I am already using edge detection image filters, but I thought it best to explain with a simple example.
Basically what I'm looking to do is detect lines in an image, and store the result in a data type where by I have say a class called Line, and various different Point objects (containing X/Y coordinates).
class Line
{
Point points[];
}
class Point
{
int X, Y;
}
And this is how I'd like to use it...
Line line;
for each pixel in image
{
if pixel should be added to line
{
add pixel coordinates to line;
}
}
I have no idea how to approach this as you can probably establish, so pointers to any subject matter would be greatly appreciated.
I'm not sure if I'm interpreting you right, but the standard way is to use a Hough transform. It's a two step process:
From the given image, determine whether each pixel is an edge pixel (this process creates a new "binary" image). A standard way to do this is Canny edge-detection.
Using the binary image of edge pixels, apply the Hough transform. The basic idea is: for each edge pixel, compute all lines through it, and then take the lines that went through the most edge pixels.
Edit: apparently you're looking for the boundary. Here's how you do that.
Recall that the Canny edge detector actually gives you a gradient also (not just the magnitude). So if you pick an edge pixel and follow along (or against) that vector, you'll find the next edge pixel. Keep going until you don't hit an edge pixel anymore, and there's your boundary.
What you are talking about is not an easy problem! I have found that this website is very helpful in image processing: http://homepages.inf.ed.ac.uk/rbf/HIPR2/wksheets.htm
One thing to try is the Hough Transform, which detects shapes in an image. Mind you, it's not easy to figure out.
For edge detection, the best is Canny edge detection, also a non-trivial task to implement.
Assuming the following is true:
Your image contains a single shape on a background
You can determine which pixels are background and which pixels are the shape
You only want to grab the boundary of the outside of the shape (this excludes donut-like shapes where you want to trace the inside circle)
You can use a contour tracing algorithm such as the Moore-neighbour algorithm.
Steps:
Find an initial boundary pixel. To do this, start from the bottom-left corner of the image, travel all the way up and if you reach the top, start over at the bottom moving right one pixel and repeat, until you find a shape pixel. Make sure you keep track of the location of the pixel that you were at before you found the shape pixel.
Find the next boundary pixel. Travel clockwise around the last visited boundary pixel, starting from the background pixel you last visited before finding the current boundary pixel.
Repeat step 2 until you revisit first boundary pixel. Once you visit the first boundary pixel a second time, you've traced the entire boundary of the shape and can stop.
You could take a look at http://processing.org/ the project was created to teach the fundamentals of computer programming within a visual context. There is the language, based on java, and an IDE to make 'sketches' in. It is a very good package to quickly work with visual objects and has good examples of things like edge detection that would be useful to you.
Just to echo the answers above you want to do edge detection and Hough transform.
Note that a Hough transform for a circle is slightly tricky (you are solving for 3 parameters, x,y,radius) you might want to just use a library like openCV