Android Draw a circle and detect bound of image - android

Now , i have the circle and image on the canvas
Ping-pong board and Ping-pong ball (draw by drawCircle)
The position of ball will depend on the accelerator
is possible to detect whether the ball the outside the board or not?
Or, i need to draw the board Programmatically without using the image

What you are looking for is called 'Collision Detection'. A technique used in game programming where the boundaries (area that defines where the object can be hit) are and then if an object enters those positions.
You can do this simply by saying that the boundaries are anything in the height / width of the image on the canvas. But I suspect that in your game you will want a subsection of that.
You will need to define a related object to your image that holds the 'Collision Boundary'. On a 2D game that will be the starting X,Y and then the height and width. While on a 3D game you will also need to store the Z position.
This is probably quite confusing to start with but I found you this little guide that explains it in more detail than I have space for here:
http://www.kilobolt.com/day-4-collision-detection-part-1.html
Let me know if you have any questions and the game sounds exciting!

Related

Android game board with irregular board spaces

I'm creating an Android board game with several differently shaped board spaces (like Risk).
I want to be sure that my board appears correct and that OnTouchListeners stay in place on the GUI regardless of screen size/resolution.
Possible solutions I have thought of and their problems:
Create a single image for the board and assign OnTouchListeners based upon pixel geometry. Problem: If the user's display is a different resolution, my Listener might not be under the same pixels as my image (right?)
Create several ImageButtons and arrange them together. Problem: the ImageButtons might get rearranged based upon the display and I would end up with overlapping spaces or gaps.
Use Android custom drawing. If I do this, how would I link my Listeners to my Canvas and be sure that they are synced?
Basic question:
How to be sure that listeners sync with graphics in a GUI that uses irregular geometry?
I worked on an app with irregular touch areas so I can give you guidance on one way to achieve this.
Start with a single image for your entire board. This image is going to have a certain ("intrinsic") width and height regardless of any device resolutions.
Now here comes the tedious part. You (or maybe your graphic designer) will need to plot out coordinates of an irregular polygon for each touch area. These will be constants to your application.
When you are displaying your board, if you are zooming and panning on the image, you want to keep track of the transform matrix for the display. When the user touches the screen, you will get x,y coordinates from OnTouchListener and for those to be useful, you will have to "de-transform" the x,y to normalize it against the intrinsic dimensions of the board and your polygons.
We rolled our own hit-testing logic using an algorithm from http://alienryderflex.com/polygon/, but you can also try this: Create a Path out of your polygon coordinates (using moveTo(), lineTo(), and close()), then assign the Path to a Region using Region.setPath(). Once you have that, supposedly you should be able to hit-test using Region.contains(x,y), but I've never tried it so I can't guarantee that's going to work.

how to attach overlay to detected object using android and OpenCV

I'm writing an android app using OpenCV for my masters that will be something like a game. The main goal is to a detect a car in selected area. The "prize" will be triggered randomly while detecting cars. When the user will hit the proper car I want to display a 3D object overlay on the screen and attach it to the middle of the car and keep it there so when the user will change the angle of his view on the car, the object will also be seen from diffrent angle.
at the moment I have EVERYTHING beside attaching the object. I've created detection, I'm drawing the 3D overlay, I've created functions that allow me to rotate the camera etc. BUT I do not have any clue how can I attach the overlay to the specific point. Cause I don't have this I have no point to recalculate the renderer to change the overlay perspective.
Please, I really need some help, even a small idea will be fine:
How can I attach the overlay to the specific in real world
(Sorry, I couldn't comment. Need at least 50 points to do that ... :P )
I assume your image of the car is coming from a camera feed and you are drawing 3d car in opengl. If so, then you can try this:
You set the pixel format of the opengl layer as RGBA_8888, so that you can set the background of the opengl camera as a transparent color.
You take a relative layout as layout of your activity.
first you add the opencv camera layout to it as full height and width.
then you add opengl layer as full height and width.
you get the position of the real car from opencv layer as pixel value or something you did.
then scale it to your opengl parameters so that you can draw it on the right spot.
it worked for me. hope it works for you too.

Collision detection for rotated bitmaps on Android

I need pixel-perfect collision detection for my Android game. I've written some code to detect collision with "normal" bitmaps (not rotated); works fine. However, I don’t get it for rotated bitmaps. Unfortunately, Java doesn’t have a class for rotated rectangles, so I implemented one myself. It holds the position of the four corners in relation to the screen and describes the exact location/layer of its bitmap; called "itemSurface". My plan for solving the detection was to:
Detect intersection of the different itemSurfaces
Calculating the overlapping area
Set these areas in relation to its superior itemSurface/bitmap
Compare each single pixel with the corresponding pixel of the other bitmap
Well, I’m having trouble with the first one and the second one. Does anybody has an idea or got some code? Maybe there is already code in Java/Android libs and I just didn’t find it.
I understand that you want a collision detection between rectangles (rotated in different way). You don't need to calculate the overlapping area. Moreover, comparing every pixel will be ineffective.
Implement a static boolean isCollision function which will tell you is there a collision between one rectangle and another. Before you should take a piece of paper do some geometry to find out the exact formulas. For performance reasons do not wrap a rectangle in some Rectangle class, just use primitive types like doubles etc.
Then (pseudo code):
for (every rectangle a)
for (every rectangle b)
if (a != b && isCollision(a, b))
bounce(a, b)
This is O(n^2), where n is number of rectangles. There are better algorithms if you need more performance. bounce function changes vectors of moving rectangles so that imitates a collision. If the weight of objects was the same (you can aproximate weight with size of the rectangles), you just need to swap two speed vectors.
To bounce elements correctly you could need to store auxiliary table boolean alreadyBounced[][] to determine which rectangles do not need a change of their vectors after bounce (collision), because they were already bounced.
One more tip:
If you are making a game under Android you have to watch out to not allocate memory during gameplay, because it will faster invoke GC, which takes a long time and slow downs your game. I recommend you watching this video and related. Good luck.

How to project a picture onto a bubble surface programmatically

I want to implement an effect that, showing a picture on a bubble surface with the picture looks like surrounding the bubble surface. But I don't know how to do this kind of things...
I am doing it in Android platform, should I use OpenGL ES for this ? Or just some 2D transformation can achieve this effect ?
One more question is, I want to create many interesting graphics effects like the PhotoShop's various filter, is there any books/articles I can refer for this kind of things ? Is this kind of work belongs to the "Digital Image Processing" field or some other computer graphics related fields ?
Or just some 2D transformation
This effect is a nonlinear transformation, so doing through the 2D (linear) transformations being available will not work. You can do it using OpenGL by numerous ways. I'm currently thinking about some easy to understand way to convey, what you need to do. Basically you need to implement some kind of refraction or nonlinear radial warp.
Say p is the center of your bubble (in 2D), and r the position relative to p, then the undistorted picture is given by r+p. Now you want to distort it toward the edges. A parabolic distortion comes to mid, i.e. instead of r+p you'd show the pixel r + (|p|^2)*p/|p|

Android: how to have an animation on top of a background image

What I'm trying to do is have a background image, for sake of simplicity, lets say it's a picture of the front of a house. Then, I want to have a red ball move from window to window.
**I want to have a background picture, and a picture on top of it.
**I then want to be able to tell the top picture EXACTLY where to go.
How can I do this?
I'm just beginning to learn about animations in Android, and have not yet run across any way to do this.
There are two routes to animation in android: Canvas and OpenGL ES.
I would recommend OpenGL for anything requiring smoothness and speed, like a moving ball.
You should create a view using the helper class GLSurfaceView
http://android-developers.blogspot.com/2009/04/introducing-glsurfaceview.html, and implement a Renderer.
I assume you have the images saved in your res/drawable folders, in a format like png and the ball file contains an alpha channel.
You can see many tutorials online, but basically you need to load your background image and your ball resource at onSurfaceCreated and store it in a texture using GLUtils.texImage2D.
In the onDrawFrame method, you should set up a 2D projection such as glOrtho2D, then draw the background.
Then just before you draw the ball texture, you can use the glTranslate(x,y,0) function to move the ball over the house. Use an alpha blend for the ball:
glBlendFunc(GL_SRC_ALPHA, GL_SRC_ONE_MINUS_ALPHA);
glEnable(GL_BLEND);
Unfortunately writing in OpenGL isn't as straightforward as you might hope. Everything is done with 3D coordinates, despite the fact you want only a 2D image. But hopefully this gives you enough info to google for good exmaples, which are abundant!

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