Android canvas game, game speed

Android canvas game, game speed - android

I have a simple function that increases the speed of my object in the screen:
float Velocity = 10;
float MaxVelocity = 100;
float VelocityGiven = 0;
RectF position = new RectF(ScreenHeight/2, ScreenWidth,0,0);
public void update()
{
if(VelocityGiven < MaxVelocity)
{
Position.left -= Velocity;
VelocityGiven += Velocity;
}
}
public void draw(Canvas canvas)
{
canvas.drawBitmap(Bitmap,Position,null);
}
But depending on the phone screen size, or pixel density, this function moves the object too fast or too slow.
if I try that on a galaxy S4, witch has a really big screen resolution, the object goes slowly.
But if I try it on a low end device (small screens), the object goes very fast,
What can I do to avoid that?
I already have my FPS controlled, on every phone, this runs at 30 FPS. so it's not about the update ratio.

It depends on what you wish to do exactly. One simple approach would be to make everything proportional to screen size. For instance:
Position.left -= Velocity * getWidth() / REFERENCE_WIDTH;
where REFENRENCE_WIDTH corresponds to a screen resolution where your app behaves as you like.

You need to work with density independent units. That way it moves the same relative amount no matter what the pixel size is. To do this, decide how "big" your area is going to be. For example, to fix your width at a logical 1000 units:
float scaleWidth = (screenWidth / 1000);
float velocity = 10 * scaleWidth;
float maxVelocity = 100 * scaleWidth;
This would mean that no matter how wide the display actually is, at max velocity it would take 10 movements to go all the way across.

You are probably best to move your objects based on a grid system independent of the screen size. You could you meters, feet, or what ever works as your unit. Then get the screen size and screen resolution of the device and figure out what the relationship is. If your object moves one foot then how many pixels is that on the device. Based on resolution.
Here is a very general overview on screen sizes for android:
http://developer.android.com/guide/practices/screens_support.html
There are probably a lot more, and better, places to look for getting the device resolution and size.
Hope that at least gets you started :)

Related

Speed and distance not same on every device

I have created an Android game using a canvas, but when testing, I have found that the speed and distance of the movements such as flying up or falling down are set right on a phone with a resolution of 1920x1080 (401 ppi). But when I tested on a smaller phone with a resolution of 480 x 854 (196 ppi), I found that the movement of my sprites are a lot quicker which is affecting the gameplay. E.g. The main character sprite jumps a lot higher than I want it to.
Is there any way of keeping the speed and distance the same across all device sizes and types?
Here is some code on how I have implemented the movement:
A sprite class.
//class variables
private int GRAVITY_LIMIT = -30;
public int gravity = 0;
//gravity
if(gravity>GRAVITY_LIMIT){
gravity= gravity-2;
}
//fall
y= y-gravity;
Drawing the sprite
canvas.drawBitmap(bmp1, x, y, null);
When onTouch is triggered (Jumping)
bird.gravity=30;

You should base your movement around world coordinates. For example, set your world to be 10meters x 10meters, so that when you jump, you jump 1m. You then need to map that world to screen pixels.
float worldHeight = 10f;
float worldToPixels = screenHeight/worldHeight;
y = bird.y * worldToPixels;
So, on a 500px height screen, you would jump 50px and on a 1000px height screen you would jump 100px.
Gravity and other forces need to be based on the world as well for it to work on all devices.
Lastly, if you're trying to make a game for multiple devices, it would be better to use a library like libGDX. There are lots of helpful classes like ViewPorts to make this easier.

I have found another solution.
This one works well.
y= y-(gravity * game.getResources().getDisplayMetrics().density);

Calculating Velocity

I am working on a very simple Physics game for Android where an object bounces up and down with some gravity (0 friction, ball should always reach same height). I want it to reach the same height on all devices (density independence). My game is coded with the following for the physics, which works perfectly fine on a 540 * 960 device.
Note: My game has a max FPS of 30
physics code
//Instance variables
private final float acceleration = .1f;
private static float timePoint;
private float velocityY = 0;
//game loop code
timePoint += 1;//updates every tick
velocityY = velocityY - acceleration * timePoint;
position.y = (int) (position.y - velocityY);
if(position.y + bitMapHeight <= 0){
velocityY = 30;
timePoint = 0;
}
When the ball hits the ground (y = 0) I simply apply a velocity of 30, which makes the ball reach a desired height on the 540 * 960 device. Of course multiple devices lead to major headaches, and this formula will not suite all of them. I think the best approach would be to somehow calculate the velocity based on screen height, but I'm not really sure what the best approach is for something like this. Below are some screenshots showing whats happening.
If anyone can point me in the right direction I would be very grateful! Please let me know if any more details are required.

I had to solve a similar problem in a 2D game I was working on a while ago.
I developed the initial physics and rendering functionality on my own Android device until it behaved nicely on that particular device. I then obtained 'baseline' values for the relevant variables (eg. pixels:meter as mentioned by bjb568), to achieve the correct velocities on my baseline device.
Then, to make the game behave in the same way on different devices/screens, I simply used the baseline values scaled by the ratio of the actual screen resolution and the baseline screen resolution.
My game used a SurfaceView, so the 'actual screen resolution' was basically determined by the width and height of the surface.
I hope that helps.

Why don't you try this on the onCreate:
Display display = getWindowManager().getDefaultDisplay();
Point size = new Point();
display.getSize(size);
width = size.x;
height = size.y;
With that you can get the values of the screen and, instead of using ´velocityY = 30;´ you can set it to ´velocityY= height/10´ for example

Why you set velocityY = 30; after point reaches the bottom? I think that you should use perfectly elastic collision. So, you just need to set velocityY = -velocityY;

I apologize to those who posted on this for my delayed response. I found a solution that worked for me. Below is the approach I took.
Find the target height that the object should reach after it hits the ground (bottom of screen).
//We want the object to bounce halfway on screen
targetBounceHeight = metrics.heightPixels / 2;
Use physics calculation to find required velocity to reach point Y.
double velocityI = Math.sqrt(2 * targetBounceHeight * acceleration);
I simply find the initial velocity required, then plug it into the original code snippet dynamically instead of the value 30 (see top post). This solution has worked on all tested devices perfectly. Hope this helps someone!

How can I code my game to work on every resolution of Android devices? (with Unity)

I have a game what I made in 480x320 resolution (I have set it in the build settings) in Unity. But I would like to publish my game for every Android device with every resolution. How can I do it, to tell Unity to scale my game up to the device's resolution? Is it possible to do?
Thanks in advance!

The answer to your question largely depends on how you've implemented the game. If you've created it using GUI textures, then it largely depends on how you've placed/sized your objects versus screen size, which makes things a little tricky.
If the majority of your game is done using objects (such as planes, cubes, etc) then there's two methods I usually choose to use.
1) First method is very easy to implement, though doesn't always look too good. You can simply change the camera's aspect ratio to match the one you've designed your game around. So in your case, since you've designed your game at 4:3, you'd do something like this:
Camera.aspect = 4f/3f;
However, if someone's playing on a screen meant for 16:9, the game will end up looking distorted and stretched.
2) The second method isn't as easy, requiring quite a bit of work and calculations, but will give a much cleaner looking result for you. If you're using an orthographic camera, one important thing to keep in mind is that regardless of what screen resolution is being used, the orthographic camera keeps the height at a set height and only changes the width. For example, with an orthographic camera at a size of 10, the height will be set to 2. With this in mind what you'd need to do is compensate for the widest possible camera within each level (for example, have a wide background) or dynamically change the Orthographic Size of the camera until its width matches what you've created.
If you've done a 3d game with a stereoscopic camera , screen resolution shouldn't really affect how it looks, but I guess that depends on the game, so more info would be required

The way i did is to change camera viewport according to device aspect ratio
Consider you made the game for 800x1280
The you can do this in any one of the script
float xFactor = Screen.width / 800f;
float yFactor = Screen.height / 1280f;
Camera.main.rect=new Rect(0,0,1,xFactor/yFactor);
and this works like magic

A easy way to do this is considering your target, I mean if you're doing a game for Iphone 5 then the aspect ratio is 9:16 v or 16:9 h.
public float targetRatio = 9f/16f; //The aspect ratio you did for the game.
void Start()
{
Camera cam = GetComponent<Camera>();
cam.aspect = targetRatio;
}

Here is my script for scaling the ortographic camera in 2D games
public float screenHeight = 1920f;
public float screenWidth = 1080f;
public float targetAspect = 9f / 16f;
public float orthographicSize;
private Camera mainCamera;
// Use this for initialization
void Start () {
// Initialize variables
mainCamera = Camera.main;
orthographicSize = mainCamera.orthographicSize;
// Calculating ortographic width
float orthoWidth = orthographicSize / screenHeight * screenWidth;
// Setting aspect ration
orthoWidth = orthoWidth / (targetAspect / mainCamera.aspect);
// Setting Size
Camera.main.orthographicSize = (orthoWidth / Screen.width * Screen.height);
}

I assume it's 2D instead of 3D, this what I do:
Create a Canvas object
Set the Canvas Scaler to Scale with Screen Size
Set the Reference Resolution to for example: 480x320
Set the Screen Match Mode to match width or height
Set the match to 1 if your current screen width is smaller (0 if height is smaller)
Create an Image as background inside the Canvas
Add Aspect Ratio Fitter script
Set the Aspect Mode to Fit in Parent (so the UI anchor can be anywhere)
Set the Aspect Ratio to 480/320 = 1.5
And add this snippet on main Canvas' Awake method:
var canvasScaler = GetComponent<CanvasScaler>();
var ratio = Screen.height / (float) Screen.width;
var rr = canvasScaler.referenceResolution;
canvasScaler.matchWidthOrHeight = (ratio < rr.x / rr.y) ? 1 : 0;
//Make sure to add Using Unity.UI on top of your Aspect Ratio Script!
For 3D objects you can use any of the answers above

The best solution for me is to use the theorem of intersecting lines so that there is neither a cut-off on the sides nor a distortion of the game view. That means that you have to step back or forward depending on the different aspect ratio.
If you like, I have an asset on the Unity asset store which automatically corrects the camera distance so you never have a distortion or a cut off no matter which handheld device you are using.

strange behaviour of live wallpaper in preview [duplicate]

I am learning how to make live wallpapers, but I have a dilemma I'm sure all who start off have as well.
There is so many resolution screen sizes, how can I just make one set of artwork to be rescaled in code for all versions? I know it's been done as I seen the images in the apk's on a lot of them and they get rescaled.
If it was just one image that did not need any positioning that would be easy, but my problem is I have to get the background image rescaled to fit all devices, I also have animations that fit in a certain x and y position on that background image to fit in place so it looks like the whole background is being animated but only parts of it is (my way of staying away from 300 images of frame by frame live wallpapers).
So the background image needs to be rescaled and the animations need to be rescaled as well to the exact percentage as the background image and they need to sit in a specific x and y position.
Any help would be appreciated so I can get this going.
I tired a few things, figured I would make a scaler for everything example: int scaler; then in onSurfaceChanged scaler = width /1024; //if the bigger image is 1024. that will give me a ratio to work with everywhere. then scale accordingly using scaleBitmap by multiplying the scaler by the image height and width, and also use the same scaler for positioning example image x lets say is at 50, scale it using the same thing x = scaler * 50; that should take care of scaling and positioning, just how to translate all this into java is the next lesson, since I'm new to java, I used to program for flash and php but this is a lot different, take some getting used to. Next thing is how to pan the width, when you move your screen from side to side how to make the image show is the next puzzle I have figure out. Right now it just shows the same width no matter what even though the width is double what the surface shows. If you got an answer or somewhere I can find out the info on this one that would be greatly appreciated.

Well, um, all I can say is "Welcome to the real world." You get your screen dimensions passed to you via onSurfaceChanged, and yes, it is your job to figure out how to scale everything based on this data. That's why they pay us the big bucks. :-)
You will want to make sure your resources are large enough to fit the biggest display you intend to support, so you will always be shrinking things (which distorts much less than expanding things).
Suggest starting with "best practices for screen independence" here: http://developer.android.com/guide/practices/screens_support.html
Additional comments in re your request for more help...
You cannot (necessarily) scale your artwork just using the width, because you need to support multiple aspect ratios. If the screen proportions do not match your artwork, you must decide if you want to distort your artwork, leave blank spaces, etc.
I'm not sure how to interpret your trouble passing around the screen dimensions. Most of us put all of our active code within a single engine class, so our methods can share data via private variables. For example, in the Cube wallpaper in the SDK, onSurfaceChanged() sets mCenterX for later use in drawCube(). I suggest beginning with a similar, simple approach.
Handling scrolling takes some "intelligence" and a careful assessment of the data you receive via onOffsetsChanged(). xStep indicates how many screens your launcher supports. Normally xStep will be 0.25, indicating 5 screens (i.e. xOffset = 0, 0.25, 0.5, 0.75, or 1) but it can be any value from 0 to 1; 0.5 would indicate 3 screens. xPixels gives you an indication of how much the launcher "wants" you to shift your imagery based on the screen you're on; normally you should respect this. On my phone, the launcher "desires" a virtual wallpaper with twice the pixels of the physical screen, so each scroll is supposed to shift things only one quarter of one screen's pixels. All this, and more, is documented in http://developer.android.com/reference/android/app/WallpaperManager.html
This is not "easy" coding--apps are easier than wallpaper. :-)
Good luck...George
P.S. I'll throw in one more thing: somewhere along the line you might want to retrieve the "desired minimum width" of the wallpaper desired by the launcher, so you can explicitly understand the virtualization implicit in xPixels. For example, in my engine constructor, I have
mContext = getApplicationContext();
mWM = WallpaperManager.getInstance(mContext);
mDW = mWM.getDesiredMinimumWidth();
My device has 320 pixel width; I get mDW = 640; as I scroll from screen to screen, xPixels changes by 80 each time...because four scrolls (across five screens) is supposed to double the amount of revealed artwork (this effect is called "parallax scrolling"). The rightmost section has xPixels equals 0; the center (of five) sections has xPixels = -160, etc.

I've used this code snippet to scale one image to fit on different screen sizes.
Bitmap image1, pic1;
image1 = BitmapFactory.decodeResource(getResources(), R.drawable.image1);
float xScale = (float) canvas.getWidth() / image1.getWidth();
float yScale = (float) canvas.getHeight() / image1.getHeight();
float scale = Math.max(xScale, yScale); //selects the larger size to grow the images by
//scale = (float) (scale*1.1); //this allows for ensuring the image covers the whole screen.
scaledWidth = scale * image1.getWidth();
scaledHeight = scale * image1.getHeight();
pic1 = Bitmap.createScaledBitmap(image1, (int)scaledWidth, (int)scaledHeight, true);
Make sure that the edges don't contain vital information as it will be scaled out of the picture on some screen ratios.

android live wallpaper rescaling

I've used this code snippet to scale one image to fit on different screen sizes.
Bitmap image1, pic1;
image1 = BitmapFactory.decodeResource(getResources(), R.drawable.image1);
float xScale = (float) canvas.getWidth() / image1.getWidth();
float yScale = (float) canvas.getHeight() / image1.getHeight();
float scale = Math.max(xScale, yScale); //selects the larger size to grow the images by
//scale = (float) (scale*1.1); //this allows for ensuring the image covers the whole screen.
scaledWidth = scale * image1.getWidth();
scaledHeight = scale * image1.getHeight();
pic1 = Bitmap.createScaledBitmap(image1, (int)scaledWidth, (int)scaledHeight, true);
Make sure that the edges don't contain vital information as it will be scaled out of the picture on some screen ratios.

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.