I am trying to calculate when the sprite which is affect by gravity starts to fall down. I presume I can get the velocity value for when it turns into a negative?
Is it something like this if I was trying to get the current velocity of a sprite on the Y axis?
_sprite.physicsbody.velocity.y
So if I had it in the update method
int velocityY = //Whatever I need to do to get the velocity.
Put both together, and use to proper data type, and you're in business:
CGFloat velocityY = _sprite.physicsBody.velocity.y;
if (velocityY < 0.0)
{
// moving down ...
}
Related
I'm currently working on a 2D platformer and I'm wondering if I can get any tips on how to increase the speed that an object moves at for a few seconds after it collides with another object.
First you need a variable called velocity
Vector2 velocity = new Vector2(0.0f, 0.0f);
Every update, you change the Rectangle of the sprite by the velocity.
rectangle.X += (int)velocity.X;
rectangle.Y += (int)velocity.Y;
Then, you can change the velocity however you like and it will change the speed.
//slow down
velocity.X -= 10;
velocity.Y -= 10;
//speed up
velocity.X += 10;
velocity.Y += 10;
You can also change the X and Y values for velocity individually, like this:
velocity.Y += 10;
That will make the sprite move down when typed in.
Hope this helped! Tell me if you need any clarification!
First you want to have it react to the collision, so in the method you're using to detect the collision, add a call to a new method in your object. Let's call it SpeedUp(). It should look something like this:
public void SpeedUp()
{
_speedUpTimer = 0;
IsSpedUp = true;
_maxVelocity.X = SpedUpVelocity.X;
}
where _speedUpTimer is a variable in your object's class (or whatever component handles movement), _maxVelocity is whatever variable maintains your object's top speed, and SpedUpVelocity is the constant or variable holding the faster velocity. IsSpedUp should be initialized as false. You're also going to want a constant or variable to hold the amount of time you want the object to be faster, such as SpeedUpTime.
Then, in your object's Update(), add the lines
_speedUpTimer += gameTime.ElapsedGameTime.Milliseconds;
if (IsSpedUp && _speedUpTimer > SpeedUpTime)
{
_maxVelocity.X = UsualMaxVelocity.X;
IsSpedUp = false;
}
UsualMaxVelocity will hold your object's previous, non-sped-up maximum velocity, which your object will return to using after the timer is up.
Of course, you can always make your Y velocity increase, but I assumed you just wanted horizontal speed.
This is language-agnostic question, more about model of my game.
I have a snake game with elements, but I move the elements smoothly, they don't just move 1 block each time, but instead they move some amount of pixels every frame.
I have an update loop that calculates the positions of the element, but I am stuck on correct calculations.
I have heading for each element:
typedef NS_ENUM(int, kElementHeading)
{
kElementHeadingNorth = 1,
kElementHeadingSouth,
kElementHeadingEast,
kElementHeadingWest
};
I also have velocity (x, y) that determines in what direction snake is going. I have problem with snake movement, because my elements are in wrong positions. I managed to localize the thing for 2 elements, but my solution fails on more elements.
First solution I tried is to save point of rotation where the head changes direction. This worked, but due to different circumstances element can move different amount of pixels each turn. Often the element would skip the point. I tried increasing the zone where it should rotate, but it adds up error. I tried fixing this error, but element would still separate from snake (quite often).
On the second try I decided to keep the snake head in center of the screen and move the world around it. It worked good for 2 elements, as I just smoothly move the next element to desired position relatively to head. But this fails badly on more elements. If you make fast turns they start dancing and not following the path.
Third thing that I tried is leaving a path for other elements to follow. But that didn't work because I intend to keep my snake on center of the screen and technically it never moves to create a path.
I'm looking to replicate the movement pattern like in Nimble Quest (or any snake).
How should I implement snake elements moving to have no errors?
Here is my code for the first method, problem with it is that often the elements would fall off. The code is pretty self-explanatory. Rotation points are the places where to change direction.
CFTimeInterval delta = self.lastTime - currentTime;
CGPoint currentPosition = self.playerSnake.head.sprite.position;
CGPoint velocity = self.playerSnake.velocity;
self.playerSnake.head.sprite.position = CGPointMake(currentPosition.x + velocity.x * delta * CONSTANTSPEEDFACTOR , currentPosition.y + velocity.y * delta * CONSTANTSPEEDFACTOR);
for (SnakeElement *element in self.playerSnake.elements) {
CGPoint currentPositionE = element.sprite.position;
CGPoint velocityE = element.velocity;
element.sprite.position = CGPointMake(currentPositionE.x + velocityE.x * delta * CONSTANTSPEEDFACTOR , currentPositionE.y + velocityE.y * delta * CONSTANTSPEEDFACTOR);
}
BOOL markToDelete = NO;
NSDictionary *deleteDictionary;
for (NSDictionary *dict in self.playerSnake.rotationPoints) {
CGPoint positionCoordinate = CGPointFromString(dict[#"position"]);
CGPoint velocityNew = CGPointFromString(dict[#"velocity"]);
double newAngle = [dict[#"angle"] doubleValue];
for (SnakeElement *element in self.playerSnake.elements) {
int xDifference = element.sprite.position.x - positionCoordinate.x;
int yDifference = element.sprite.position.y - positionCoordinate.y;
if ((xDifference > -2 && xDifference < 2) && (yDifference > -2 && yDifference < 2) ) {
element.velocity = velocityNew;
element.sprite.position = CGPointMake(element.sprite.position.x + xDifference, element.sprite.position.y + yDifference);
SKAction *action = [SKAction rotateToAngle:newAngle duration:0.2 shortestUnitArc:YES];
[element.sprite runAction:action];
if ([element isEqual:[self.playerSnake.elements lastObject]]) {
markToDelete = YES;
deleteDictionary = dict;
}
}
}
}
[self.playerSnake.rotationPoints removeObject:deleteDictionary];
If I try increase the catch zone for the turning point, the elements tend to fall off more often then when it is 1 or 2 pixels wide. I'm not sure why this happens.
This is what I was suggesting you do in the comments in terms of handling your turning on points :
1.. calculate the distance that the element should move that frame based on speed and your elapsed time since last frame. (delta)
2.. calculate distance from element's current position to the turn point. This is the beforeDistance I spoke of in the comments
3.. calculate the distance the element should move towards the NEW target turning point AFTER the turn
afterDistance = distanceToMoveThisFrame - beforeDistance
4.. Calculate the new position for your element, starting at the current turning point towards the next target turning point of the element using afterDistance
If you follow this logic, you will NEVER overshoot or undershoot the turning point.
I'm making an app that (among other things) displays a simplified compass image that rotates according to the device's rotation. The problem is that simply doing this:
float heading = -1.0f * M_PI * trueHeading / 180.0f; //trueHeading is always between 0 and 359, never 360
self.compassNeedle.transform = CGAffineTransformMakeRotation(heading);
inside CLLocationManager's didUpdateHeading method makes the animation ugly and choppy.
I have already used Instruments to find out whether its simply my app not being able to render at more than 30-48 fps, but that's not the case.
How can I smooth out the image view's rotation so that it's more like Apple's own Compass app?
Instead of using the current instant value, try using the average of the last N values for the true heading. The value may be jumping around a lot in a single instant but settle down "in the average".
Assuming you have a member variable storedReadings which is an NSMutableArray:
-(void)addReading(float):newReading
{
[storedReadings addObject:[NSNumber numberWithFloat:newReading]];
while([storedReadings count] > MAX_READINGS)
{
[storedReadings removeObjectAtIndex:0];
}
}
then when you need the average value (timer update?)
-(float)calcReading
{
float result = 0.0f;
if([storedReadings count] > 0)
{
foreach(NSNumber* reading in storedReadings)
{
result += [reading floatValue];
}
result /= [storedReadings count];
}
return result;
}
You get to pick MAX_READINGS a priori.
NEXT LEVEL(S) UP
If the readings are not jumping around so much but the animation is still choppy, you probably need to do something like a "smooth" rotation. At any given time, you have the current angle you are displaying, theta (store this in your class, start it out at 0). You also have your target angle, call it target. This is the value you get from the smoothed calcReading function. The error is defined as the difference between the two:
error = target-theta;
Set up a timer callback with a period of something like 0.05 seconds (20x per second). What you want to do is adjust theta so that the error is driven towards 0. You can do this in a couple of ways:
thetaNext += kProp * (target - theta); //This is proportional feedback.
thetaNext += kStep * sign(target-theta); // This moves theta a fixed amount each update. sign(x) = +1 if x >= 0 and -1 if x < 0.
The first solution will cause the rotation to change sharply the further it is from the target. It will also probably oscillate a little bit as it swings past the "zero" point. Bigger values of kProp will yield faster response but also more oscillation. Some tuning will be required.
The second solution will be much easier to control...it just "ticks" the compass needle around each time. You can set kStep to something like 1/4 degree, which gives you a "speed" of rotation of about (1/4 deg/update) * (20 updates/seconds) = 5 degrees per second. This is a bit slow, but you can see the math and change kStep to suit your needs. Note that you may to "band" the "error" value so that no action is taken if the error < kStep (or something like that). This prevents your compass from shifting when the angle is really close to the target. You can change kStep when the error is small so that it "slides" into the ending position (i.e. kStep is smaller when the error is small).
For dealing with Angle Issues (wrap around), I "normalize" the angle so it is always within -Pi/Pi. I don't guarantee this is the perfect way to do it, but it seems to get the job done:
// Takes an angle greater than +/- M_PI and converts it back
// to +/- M_PI. Useful in Box2D where angles continuously
// increase/decrease.
static inline float32 AdjustAngle(float32 angleRads)
{
if(angleRads > M_PI)
{
while(angleRads > M_PI)
{
angleRads -= 2*M_PI;
}
}
else if(angleRads < -M_PI)
{
while(angleRads < -M_PI)
{
angleRads += 2*M_PI;
}
}
return angleRads;
}
By doing it this way, -pi is the angle you reach from going in either direction as you continue to rotate left/right. That is to say, there is not a discontinuity in the number going from say 0 to 359 degrees.
SO PUTTING THIS ALL TOGETHER
static inline float Sign(float value)
{
if(value >= 0)
return 1.0f;
return -1.0f;
}
//#define ROTATION_OPTION_1
//#define ROTATION_OPTION_2
#define ROTATION_OPTION_3
-(void)updateArrow
{
// Calculate the angle to the player
CGPoint toPlayer = ccpSub(self.player.position,self.arrow.position);
// Calculate the angle of this...Note there are some inversions
// and the actual image is rotated 90 degrees so I had to offset it
// a bit.
float angleToPlayerRads = -atan2f(toPlayer.y, toPlayer.x);
angleToPlayerRads = AdjustAngle(angleToPlayerRads);
// This is the angle we "wish" the arrow would be pointing.
float targetAngle = CC_RADIANS_TO_DEGREES(angleToPlayerRads)+90;
float errorAngle = targetAngle-self.arrow.rotation;
CCLOG(#"Error Angle = %f",errorAngle);
#ifdef ROTATION_OPTION_1
// In this option, we just set the angle of the rotated sprite directly.
self.arrow.rotation = CC_RADIANS_TO_DEGREES(angleToPlayerRads)+90;
#endif
#ifdef ROTATION_OPTION_2
// In this option, we apply proportional feedback to the angle
// difference.
const float kProp = 0.05f;
self.arrow.rotation += kProp * (errorAngle);
#endif
#ifdef ROTATION_OPTION_3
// The step to take each update in degrees.
const float kStep = 4.0f;
// NOTE: Without the "if(fabs(...)) check, the angle
// can "dither" around the zero point when it is very close.
if(fabs(errorAngle) > kStep)
{
self.arrow.rotation += Sign(errorAngle)*kStep;
}
#endif
}
I put this code into a demo program I had written for Cocos2d. It shows a character (big box) being chased by some monsters (smaller boxes) and has an arrow in the center that always points towards the character. The updateArrow call is made on a timer tick (the update(dt) function) regularly. The player's position on the screen is set by the user tapping on the screen and the angle is based on the vector from the arrow to the player. In the function, I show all three options for setting the angle of the arrow:
Option 1
Just set it based on where the player is (i.e. just set it).
Option 2
Use proportional feedback to adjust the arrow's angle each time step.
Option 3
Step the angle of the arrow each timestep a little bit if the error angle is more than the step size.
Here is a picture showing roughly what it looks like:
And, all the code is available here on github. Just look in the HelloWorldLayer.m file.
Was this helpful?
I'm currently trying to make a basic platformer with XNA and I'm wondering how to create a "jumping effect." I currently have basic keyboard input which allows for sideways movement, but I would like my sprite to slowly progress into a jump rather than instantly teleporting there (right now I have something like Rectangle.Y += 40 every time I jump, making the sprite instantly appear there). Does anyone have any insight?
I'm not totally across how to implement this in XNA/C#, but in Flash games I've made I just added a vertical velocity property. I'll try write everything as C# as I can..
Example; create the velocity property:
float verticalVelocity = 0;
Vertical velocity should be constantly reduced (by gravity). Set up a gravity property somewhere accessible from your player:
float Gravity = 2.5;
And in your update() method for the player, increment the verticalVelocity by Gravity. Also increment the Y position of your player by the verticalVelocity. This will simulate falling:
verticalVelocity += Gravity;
Position.Y += verticalVelocity; // this may be -= in XNA, not sure where the y axis beings
When you hit a surface, the velocity should be reset to 0.
And finally, to jump, simply subtract a given value from verticalVelocity:
public void Jump(float height)
{
// Only jump if standing on a surface.
if(verticalVelocity == 0)
verticalVelocity -= height;
}
You'll eventually want to add gravity and possibly other forces to your game, so I highly recommend you save yourself a lot of pain and implement some kind of basic force system. This can be done using Vector2s, as you can just add them to the speed of your character. Then just apply an instantaneous force to your character to push it up.
If you really don't want to use a physics engine, you can make a Vector2 with the high point of the jump for the Y and the characters X, and then use the Vector2.Lerp method to interpolate between the characters position and the end point of the jump.
This is generally a very bad system to use, and I highly recommend you either use an existing physics engine, or make your own simple one.
use a sinusoidcode should look something like this:
float ground = 0.0f;
float angle = 330.0f;
jump(){
if(ground == 0.0f)ground = Rectangle.Y;
if(Rectangle.Y <= ground)
{
Rectangle.Y+=Math.Sin(angle/(Math.Pi*180));
angle++;
}
}
You can accurately create a gravity effect if you modify the ySpeed dynamically, as opposed to just adding 40.
You want to declare a ySpeed
ySpeed = 0;
Then you want to use an acceleration variable
acceleration = 0.25;
Okay, now that we've done that, let's add gravity, provided that our player isn't touching the floor.
if(playerLocationY + playerHeight > floorLocationY)
{
gravity = false;
}
else
{
gravity = true;
}
if(gravity)
{
ySpeed += acceleration;
}
Now that we've got that down, we want to include something that allows us to jump.
if(KeyPressed == UP)
{
ySpeed -= acceleration;
}
This will move our player in the upward direction
We now want to make sure we actually move, so let's add one last line and we're done.
playerLocationY += ySpeed;
Congratulations, you made it.
I am really looking to try to have gravity in my game. I know everyone says use Box2D, but in my case I can't. I need to use Cocos2D for the gravity.
I know Cocos2D does not have any gravity API built in so I need to do something manually. The thing is there is like no tutorials or examples anywhere on the web that show this.
Can anyone show me what they have done or can some explain step by step on how to apply a non-constant gravity (One that gets slightly stronger while falling).
I think this will help a lot of people that are facing the same issue that I am having!
Thanks!
Gravity is nothing but a constant velocity applied to the body for every physics step. Have a look at this exemplary update method:
-(void) update:(ccTime)delta
{
// use a gravity velocity that "feels good" for your app
const CGPoint gravity = CGPointMake(0, -0.2);
// update sprite position after applying downward gravity velocity
CGPoint pos = sprite.position;
pos.y += gravity.y;
sprite.position = pos;
}
Every frame the sprite y position will be decreased. That's the simple approach. For a more realistic effect you will want to have a velocity vector for each moving object, and apply gravity to the velocity (which is also a CGPoint).
-(void) update:(ccTime)delta
{
// use a gravity velocity that "feels good" for your app
const CGPoint gravity = CGPointMake(0, -0.2);
// update velocity with gravitational influence
velocity.y += gravity.y;
// update sprite position with velocity
CGPoint pos = sprite.position;
pos.y += velocity.y;
sprite.position = pos;
}
This has the effect that velocity, over time, increases in the downward y direction. This will have the object accelerate faster and faster downwards, the longer it is "falling".
Yet by modifying velocity you can still change the general direction of the object. For instance to make the character jump you could set velocity.y = 2.0 and it would move upwards and come back down again due to the effect of gravity applied over time.
This is still a simplified approach but very common in games that don't use a "real" physics engine.