I have an Android canvas on which I'm drawing a series of lines to represent a hexagonal game board. The hexagon is subdivided with several intersecting interior lines.
I'm trying to figure out how to "cut out" a smaller hexagon from the center of the main hexagon, similar to this image: http://www.dcc.fc.up.pt/~pbv/stuff/hstzaar/hstzaar.png.
Is it possible to position a polygon over the intersecting lines and take the "difference" of the shapes, such that the lines underneath are modified to end at the polygon edges?
It might be sufficient to simply place an opaque polygon on top of the board center, but I was curious if it was possible to actually modify the underlying lines.
Since there are only 3 interior lines that run through the center of the hexagon, it's actually easier to draw each of them in two segments rather than try to cut them out later.
I'd still be interested to know if my original question was possible, but I solved the problem for now.
Related
I'm creating an Android app which simulates petri nets. I'm representing place by circle and transition by square and I'm connecting those views by arc (it's just the name from petri nets for my purpose it's just a straight line) and here's the problem I'm facing, I know how to connect the centre point of those views but i don't know how to connect the border of circle and border of square, look at the image it should explain everything:
In my app I know if I'm pointing a place (circle) or transition (square), I also know the dimension of those views and it's coordinates, can you suggest me any start point for writing an algorithm which will connect borders of those two shapes and draw the arrow at the end of the line? Thanks in advance
You can make a method that takes in an angle and returns the point on the boundary at that angle from the center. This involves a little trigonometry, and cases for the square. To draw a line between the boundaries of two shapes, determine the angle of the difference vector atan2(difference in ys, difference in xs). Choose the point on the boundary with that angle. (This chooses the point that is on the line segment connecting the centers. You can change this if you want.) Connect the two points you get with a line, and add the arrow's head.
I want to apply the border to this custom view shape
which created by many canvas.draw...() in onDraw()
The border that i want to create and apply to my custom view should have equal range all the way with some distance from the custom view and it should also cover small circle in each slice.
Any idea how to make this?
Thanks.
This isn't so much an answer, but more of a recommendation. Take a look at the Porter-Duff modes available to you. Worst case you may need to do some per pixel image manipulation which should be fine as long as the view isn't animated.
On second thought, here's an idea: why not create two images: one large circle which will always draw behind everything and a second which will always draw behind the small circles. The large circle would just be the complete border you want displayed, whereas the small circles would actually only be a semi circle border, which would render on top of the large circle (covering the large circle border under it). The key would then be to rotate the small border circle depending on where it's located. I hippie that makes sense, but it should work and be very efficient too.
Another option would be to separate the rendering into white circles and slightly larger border color circles. If you render the slightly larger (border color) circles first, then render the normal circles (white) on top, then you won't have to worry about any rotations and it will render correctly if the small outer circles begin to overlap.
So the idea is similar to the first suggestion. You'll still need a large circle and small circle (both white), but in addition, you'll need slightly larger border colored large and small circles.
I hope this description is a little clearer, but I assume that you are comfortable enough with compound drawables to figure out the rest, given that you've gotten this far in making your view.
All the best implementing it, and feel free to ask for any clarification! :)
I have a need to define a polygon that would be the "legal" area, and allow a user to move a rectangle around within that polygon, preventing them from moving the rectangle anywhere where its points venture outside the polygon.
The polygon is a fixed shape, so, I was thinking it may be easiest to import a PNG of that shape and pull the points in that way, somehow? But I'm still at a loss as to the math involved in checking the coordinates of the rectangle as the user drags it, and testing at what point they have moved the shape to the edge of the bounding polygon.
Unfortunately the bounding polygon is a fairly complex shape. I'm hoping someone can point me at a tutorial that shows what the best way to run such a collision detection is.
Metanet's excellent collision detection tutorial has a good section on how to do swept collision with axis-aligned bounding boxes (AABB) and arbitrary "walls."
If your polygon is concave, you'll probably find it easiest to first decompose it into multiple convex polygons, which will simplify the available collision detection algorithms.
If you only looking to check the corners of the rectangle, you can do a "inside" test for each of them.
http://en.wikipedia.org/wiki/Point_in_polygon
And if you also want to make sure that no pointy part of the polygon "punctures" your rectangle you could do a test for each of the 4 lines in the rectangle against all the lines in the polygon to see if they are intersecting.
http://en.wikipedia.org/wiki/Line-line_intersection
I'm trying to create a jigsaw puzzle app for Android. I am fairly far into the coding, and I am kind of stuck with one issue.
I need a way to change a Bitmap into a bunch of puzzle pieces. My current code simply cuts the image into rectangles, and it works pretty well, but now I need a way to create more complex piece shapes.
I had a couple of ideas:
Use a separate bitmap file that contains only black and white pixels, and use that to cut up the picture. I thought this was a pretty good plan, until I went to code it. I really had no idea how to do it.
Use a Path object to create the border. This would probably work, except I'm not sure how to keep track of the sides so that the pieces connect with each other.
Any ideas? I'm open to any suggestions.
You can use Path and/or Region to set a clip for your Canvas when drawing a Bitmap.
Take a look at this example. Here are some ways of clipping your drawing to any shape.
You could try making squares or rectangles fitted inside complex figures that can still be pieced toguether, when there's a match, the full rectangle covers the space. Imagine it like a 9 patch, when two sides match, you show the border rectangle.
This is not a explicit solution but I wonder if it would be possible to use bezier curves or paths to create lines along x and y , in conjunction with a parameter(fed with random value) to control the amount of deviation from a straight line and how much in a given distance ie; pixels/ per inch - this would be to create tongues on the pieces. Then use Region to extract the resulting shape at a given side of an intersection. Have the shape object get its center xy coordinate at instantiation and make it so that piece cannot be set if its current coordinate does not match the one it had when it was created.
So I'd like to be able to draw a circle where I can specify the amount of circle drawn as shown in the following diagram.
AS an opengl newbie I'm not really sure how to approach this.. I've previously drawn full circles using GL_TRIANGLE_FAN
You already know how to draw a circle using a triangle fan. Now you just have to calculate the angles of the cutoff corners, use those as the beginning and end of the arc and place the hub of the triangle fan at the middle of the cutoff edge.
you could use a glScissor test to cut off the parts of the circle that you don't want.
http://www.khronos.org/opengles/sdk/1.1/docs/man/glScissor.xml