AS3: How to intersect vectors at runtime? - actionscript-3

Let's say I use the Graphics class at runtime to draw some vector shapes dynamically. For example a square and a circle.
Is there a way to create a new shape at runtime where those 2 vectors shapes overlap?
Those kind of operations are very common in all vector design programs such as Illustrator, Corel, etc... but I haven't found anything in Adobe's documentation, nor anywhere else, to do it by code.

Although drawing operations on the Graphics class are described in terms of lines, points etc this is - as far as you're concerned - just telling it what to draw onto a bitmap. There's no way to remove a shape once drawn, short of clear(), which just wipes the whole thing clean.
I don't fully understand why, as the vector data must be retained - there's no loss of quality on scaling after drawing, for example.
If you don't want to get into some hardcore maths (for anything beyond straight lines, you'll need to) there's an answer here which might help if you've ever used PixelBender:
How to calculate intersection between shapes in flash / action script ? (access to shape's segments and nodes?)
Failing that, if it's just cosmetic you could play around with masking shapes (will probably end up quite hacky though) - however, if you actually want to use the intersection to draw or describe a shape you will need to dig out your maths book or look for a good graphics library.
Hope this helps

Related

Detect coordinates within a shape

Theres 2 parts to my problem and they are related. I have a weird shape on my interface illustrated below, I am trying to randomly spawn MovieClips within its' boundaries but I am having some trouble finding a good way to do it.
Question 1: I can run an If condition to check with bitMapData.hitTest to see if the MovieClip has randomly spawn within this shape, if it doesn't simply retry with a new set of random coordinates. However, is there a better way? Like a way to only take into account coordinates within the shape? There will be plenty of MC spawned at one go so I am hoping to lessen the load, or at least find an efficient way to do this calculation.
Question 2: The MovieClips spawned within this shape will eventually have collision detection mechanics that will repel itself when interacted with. Is there a way to contain them within this shape via some kind of boundary detection?
If it was a square, we could easily have contained them with a quick check on all 4 edges, but not with this shape. Currently I am thinking of using bitMapData.hitTest again to detect for out-of-bounds after being repelled, but how do I know which Point() is the nearest 'edge' of this shape to return the MC to?
For question 1: I'm going to go on an assumption that you have some geometry data about the shape.
One method you can use to check if a point is within a shape is to take that point, then draw a line from that point to infinity (the edge of the screen) in one direction. Then count how many times that line intersects an edge of the shape. If it's odd, the point is within the shape (or on the edge) and if it's even, than that point is outside of the shape.
First link in google: https://www.geeksforgeeks.org/how-to-check-if-a-given-point-lies-inside-a-polygon/
Or can also try a more simple method (at the cost of doing more work): if the above shape is generated with all squares and rectangles and you know the point and size of all of those: can just do a check for the point vs all the squares and rectangles that make up the shape.
For question 2: As Organis mentioned, I'd go with a library like Box2D to do this. You'll most likely spend tons of time (that you may not want to) if you try to implement this alone.
The big issue is how much cpu or gpu the code uses. You're trying to avoid using any collision detection. Collision detection is having code do calculations to determine the edges of an object. It should be the last option.
Most of the time you know there's no need for collision detection. You know where everything is and how big it is. Everything has a centerpoint and comparing simple number coordinates is the lightweight way to check if there's a need to check further.
When things get near each other, you only need to do a collision detection on the immediate area around an object. See how your shape fits in a box that is easy to check for collisions? That box should get a collision check before the actual jagged shape inside it.
Yes that collision detection box has to be drawn or mapped but it's done when the object is defined, not when the game is playing. If you are using sprite sheets, keep an xml of the boxes or circles around the shapes.

Is it possible to create a visualization like this in WebGL?

This visualization is created using Away3D (Flash):
www.guardian.co.uk/world/interactive/2011/mar/22/middle-east-protest-interactive-timeline
Would it be possible to create something of the same quality (re. interaction, animation, performance, pixel-perfection etc.) using WebGL?
Bonus: How would one set up the basic scene? (without interaction and animation)
Yes, it would be. The scene is not complex at all, so it would have good performance. Interaction, yes, depends how you implement it, but if you are doing project with, for example, Three.js it wouldn't be a problem. Pixel perfection, obviously, yes.
In the scene, you could have curved plane, with texture that is changing UVs of vertices when you use 'navigate'. Pins could be done with particle, or better, simple quads with transparent textures. To have pixel-precise pin picking, you could depth-test pins on ray trace, or use pin-shaped geometry with shader, which probably the best solution.
So, basic scene - curved plane with per-vertex-changing-UV, pin-shaped and texture pins.
Alternatively, you could do exactly the same thing with 2D canvas. All elements are just drawn and scaled, text would be much simpler, and picking would be with 2d calculations.
Hope this helps.

Flash automatically finds curve intersection points. Can I use that code like I use curveTo in actionscript?

Or do I have to get down and dirty with the math and do the spline intersection math myself? I know the basic math for Quadratic b-splines.
I'm trying to make procedural randomly generated Celtic knot-work that animates itself. I'm inspired by the book of Kells original book -and the animation of the same name. This means at best it will be seriously complicated - lots of curves animating fast. I'm going for generative -responsive to the user- Celtic knots of the highest possible complexity.... that may mean only 12 points animating randomly and in response to mouse movements but... I'd love hundreds or tens of thousands... some day.
Developing a moving random curvy double lined loop scribble was easy. I like the look of the curves made from 12 to 14 random points. Now I want to weave it over under over under. To do that -- I need to find the intersections of lots of random curves quickly for each frame. When I draw curves in Flash in the -not object- drawing mode... Flash does intersections and generates points automatically for me.
Questions:
-Is there an equivalent intersection class/method/function in Actionscript 3.0 to the intersections so easily done in the flash drawing interface?
-How much of what you do in Flash as an artist has cool classes like curveTo in Actionscript 3.0?
-Can I see the source code for curveTo?
-Can I extend the curveTo to do what I want?
-I have been reading and re-reading the reference and how to extend classes... that I made. But how to I learn how to extend curveTo ... or Path classes... can I?
Would this be something that you are looking for:
http://actionsnippet.com/?p=965
See a demo here: http://www.actionsnippet.com/swfs/bezier_intersect.html

How to draw an anti-aliased bezier curve in raster?

Does anyone know a decent algorithm for drawing a anti-aliased (smooth) quadratic bezier curves in a raster?
I could simply draw them as vectors and then copy the image to a raster..
Is there any clever yet freely available algorithm to draw the curve directly to the pixels?
I am currently using the algorithm implemented here:
http://www.bytearray.org/?p=67
quadBezier()
I am wondering if there is a way to change it to render anti-aliased bezier?
Thanks in advance.
I am doing this for learning purposes and because I am hoping it would be faster than using the copy pixels from a Shape option.
Here is an example showing the none-smooth bezier is faster than the regular bezier:
http://lab.generalrelativity.org/raster/
Implementing your own algorithm will almost certainly be slower than using bitmapData.draw(shape).
When you use graphics.lineTo, graphics.curveTo etc, you are constructing a model, but not actually drawing anything yet. It's only after the shape gets added to the stage, and during the subsequent [render] phase that the model is traversed and pixels drawn by a fast algorithm written in C. When you use bitmapData.draw to draw a vector into a bitmap, it will use the same native code. So it isn't as if you are drawing anything twice, as you might imagine, and it will be hard (or impossible) to beat for speed by implementing anything from scratch in AS3 alone.

How can I turn an image file of a game map into boundaries in my program?

I have an image of a basic game map. Think of it as just horizontal and vertical walls which can't be crossed. How can I go from a png image of the walls to something in code easily?
The hard way is pretty straight forward... it's just if I change the image map I would like an easy way to translate that to code.
Thanks!
edit: The map is not tile-based. It's top down 2D.
I dabble in video games, and I personally would not want the hassle of checking the boundaries of pictures on the map. Wouldn't it be cleaner if these walls were objects that just happened to have an image property (or something like it)? The image would display, but the object would have well defined coordinates and a function could decide whether an object was hit every time the player moved.
I need more details.
Is your game tile based? Is it 3d?
If its tile based, you could downsample your image to the tile resolution and then do a 1:1 conversion with each pixel representing a tile.
I suggest writing a script that takes each individual pixel and determines if it represents part of a wall or not (ie black or white). Then, code your game so that walls are built from individual little block, represented by the pixels. Shouldn't be TOO hard...
If you don't need to precompute anything using the map info. You can just check in runtime logic using getPixel(x,y) like function.
Well, i can see two cases with two different "best solution" depending on where your graphic comes from:
Your graphics is tiled, and thus you can easily "recognize" a block because it's using the same graphics as other blocks and all you would have to do is a program that, when given a list of "blocking tiles" and a map can produce a "collision map" by comparing each tile with tiles in the "blocking list".
Your graphics is just some graphics (e.g. it could be a picture, or some CG graphics) and you don't expect pixels for a block to be the same as pixels from another block. You could still try to apply an "edge detection" algorithm on your picture, but my guess is then that you should rather split your picture in a BG layer and a FG layer so that the FG layer has a pre-defined color (or alpha=0) and test pixels against that color to define whether things are blocking or not.
You don't have much blocking shapes, but they are usually complex (polygons, ellipses) and would be unefficient to render using a bitmap of the world or to pack as "tile attributes". This is typically the case for point-and-click adventure games, for instance. In that case, you're probably to create path that match your boundaries with a vector drawing program and dig for a library that does polygon intersection or bezier collisions.
Good luck and have fun.