I want to detect collision between two rectangles where I know the size and position for both of them. I tried this c# code inside my "brick" class that uses the center of the player and the brick as reference:
public bool IsTouchingPlayer(Player player)
{
return (player.xPos > xPos - (width / 2) && player.xPos < xPos + (width / 2)) &&
(player.yPos > yPos - (height / 2) && player.yPos < yPos + (height / 2));
}
But sadly, this only accounts for the center of the player colliding with the brick; I think it's safe to say this is a problem.
If you need more info let me know.
Related
I have a mildly interesting problem which I can't quite figure out (although in fairness, I am pretty drunk)
The "Seed of Life" is a pattern created from drawing circles of equal radius, centred on the intersection of the previous circle.
Language doesn't really matter, the theory is more important here. Anything which can draw a circle will do it. For example, HTML5 + JS canvas can do it. It's a lovely example of how recursion can help solve problems.
The problem is that a naive approach will end up redrawing many, many circles. With 7 layers, you'll end up with over 300,000 circle draws.
A simple approach is to maintain a list of previous circle centre points, and only draw circles which are not in that list.
My question is whether there's a "better" way to approach this? Something which doesn't require checking that list.
A fun problem to ponder.
I think I have this solved thanks to a friend. I'll post here what I'm doing now in case someone ever is curious.
In short, starting from the center and working out, calculate the vertices of a hexagon, and subdivide each edge of the hexagon into i number of places, where i is the layer number.
I drew it in C# using SkiaSharp, but the code is nothing special to the language, there's no reason this couldn't be written in any language. Here's the significant bits:
const float seedAngle = (float)(Math.PI / 3.0);
static void SeedOfLifeDemo(int x, int y) {
//setting up Skia stuff, this will be different depending what language you're using.
var info = new SKImageInfo(x, y);
using var bitmap = FlatImage(info, SKColors.White);
SKCanvas canvas = new SKCanvas(bitmap);
float radius = Math.Min(x, y) / 15;
SKPoint center = new SKPoint(x / 2f, y / 2f);
SKPaint strokePaint = new SKPaint {
Color = SKColors.Black,
Style = SKPaintStyle.Stroke,
StrokeWidth = 1,
IsAntialias = true,
};
int layers = 4;
//Draw the very central circle. This is just a little easier than adding that edge case to SubdividedHexagonAboutPoint
canvas.DrawCircle(center, radius, strokePaint);
for (int i = 1; i <= layers; i++) {
foreach (SKPoint p in SubdividedHexagonAboutPoint(center, radius * i, i)) {
canvas.DrawCircle(p, radius, strokePaint);
}
}
SaveImage(bitmap, "SeedOfLifeFastDemo.Jpg");//More Skia specific stuff
}
//The magic!
static List<SKPoint> SubdividedHexagonAboutPoint(SKPoint centre, float radius, int subdivisions) {
List<SKPoint> points = new List<SKPoint>(6 * subdivisions);
SKPoint? prevPoint = null;
for (int i = 0; i < 7; i++) {//Step around the circle. The 7th step is to close the last edge
float x = (float)(Math.Sin(seedAngle * i) * radius + centre.X);
float y = (float)(Math.Cos(seedAngle * i) * radius + centre.Y);
SKPoint point = new SKPoint(x, y);
if (prevPoint != null) {
points.Add(point);//include the "primary" 6 points
if (subdivisions > 0) {
float xDist = (point.X - prevPoint.Value.X) / subdivisions;
float yDist = (point.Y - prevPoint.Value.Y) / subdivisions;
for (int sub = 1; sub < subdivisions; sub++) {
SKPoint subPoint = new SKPoint(point.X - xDist * sub, point.Y - yDist * sub);
points.Add(subPoint);//include the edge subdivisions
}
}
}
prevPoint = point;
}
return points;
}
This is quite an interesting exercise really, and another example of where recursion can really bite you when used badly.
Intro
I've created a spaceship sprite in my Unity project, I wanted it to rotate towards the cursor via angular velocity, because I'd like make my game to be heavily physics based.
Problem
Now my problem with rotating the sprite via by angular velocity is the following:
At -180° / 180° rotation my ship spins around, because while my mouse's angle is already 180°, while my ship's rotation is still -180°, or the other way around.
I tried
I tried to solve it mathematically, wasn't too successful, I could make it spin the right way just much slower/faster, I could fix the 180/-180 point, but made two different ones instead.
Looked for different solutions, but couldn't find a more fitting one.
Code
So I have this code for the rotation:
// Use this for initialization
void Start () {
rb = gameObject.GetComponent<Rigidbody2D>();
}
// Update is called once per frame
void Update () {
//getting mouse position in world units
mousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
//getting the angle of the ship -> cursor vector
angle = Mathf.Atan2(mousePos.y - transform.position.y, mousePos.x - transform.position.x) * Mathf.Rad2Deg;
//getting the angle between the ship -> cursor and the rigidbody.rotation vector
diffAngle = angle - (rb.rotation + 90);
//Increasing angular velocity scaling with the diffAngle
rb.angularVelocity = diffAngle * Time.deltaTime * PlayerShipStats.Instance.speed * 100f;
Thank you for your contribution in advance
Solution for Problem 1
Inserting this code made it work, not for long :
if(diffAngle > 180) {
diffAngle -= 360;
} else if (diffAngle < -180) {
diffAngle += 360;
}
Problem 2 and Solution for Problem 2
The new problem is:
rigidbody.rotation can exceed it's boundaries, it can be rotated for more than 360 degrees.
this code patched this bug:
if(rb.rotation + 90 >= 180) {
rb.rotation = -270;
} else if (rb.rotation + 90 <= -180) {
rb.rotation = 90;
}
The perfect code
void AimAtTarget(Vector2 target, float aimSpeed) {
//getting the angle of the this -> target vector
float targetAngle = Mathf.Atan2(target.y - transform.position.y, target.x - transform.position.x) * Mathf.Rad2Deg;
if (rb.rotation + 90 >= 180) {
rb.rotation = -270;
} else if (rb.rotation + 90 <= -180) {
rb.rotation = 90;
}
//getting the angle between the this -> target and the rigidbody.rotation vector
float diffAngle = targetAngle - (rb.rotation - 90);
if (diffAngle > 180) {
diffAngle -= 360;
} else if (diffAngle < -180) {
diffAngle += 360;
}
//Increasing angular velocity scaling with the diffAngle
rb.angularVelocity = diffAngle * Time.deltaTime * aimSpeed * 100;
}
There are two problems I see here:
Problem 1
angle is always going to be between -180 and 180, while rb.rotation is between 0 and 360. So you are comparing angles using two different notations. The first step is to get both angles returning -180 to 180 or 0 to 360. I chose to do the following which puts both angles between -180 and 180:
//getting the angle of the ship -> cursor vector
float targetAngle = Mathf.Atan2(
mousePos.y - transform.position.y,
mousePos.x - transform.position.x) * Mathf.Rad2Deg;
//get the current angle of the ship
float sourceAngle = Mathf.Atan2(
this.transform.up.y,
this.transform.up.x) * Mathf.Rad2Deg;
Problem 2
If you fix problem 1 and tried your app you would notice that the ship sometimes rotates the wrong way, although it will eventually get to its target. The problem is that diffAngle can sometimes give a result that is greater than +180 degrees (or less than -180). When this happens we actually want the ship to rotate the other direction. That code looks like this:
//getting the angle between the ship -> cursor and the rigidbody.rotation vector
float diffAngle = targetAngle - sourceAngle;
//use the smaller of the two angles to ensure we always turn the correct way
if (Mathf.Abs(diffAngle) > 180f)
{
diffAngle = sourceAngle - targetAngle;
}
I made a simple Unity to verify this works. I was able to rotate my ship in either direction smoothly.
One thing you may have to handle, if you don't already, is appropriately stopping the rotation of the ship when the it is facing the cursor. In my test I noticed that the ship would jitter slightly when it reached its target because it would (very) slightly overshoot the cursor's angle in one direction and then the other. The larger the value of PlayerShipStats.Instance.speed the more pronounced this effect will likely be.
Either my coffee hasn't kicked in yet or I didn't pay enough attention in college, either way I can't wrap my head around the right way to do this calculation.
I have a maze that is made up of zones, the player can only see one zone at a time. At the moment the camera stays centered on the player, so as they nears the edge of the zone we see every expanding blackness because there is nothing there. I would like for the camera's center to stay stationary when the player gets close to the adjust of the zone.
This is the code that I have so far:
private void ResetRenderView()
{
// Make sure this control always fills the parent
this.Size = this.Parent.Size;
//Calculate and correct CellSize so the screen can always be filled
int zoneSize = DM.currentDungeon.Settings.ZoneSize;
float minCellSize = (float)this.Size.Width / (float)zoneSize;
if (cellSize < minCellSize + .5f) { cellSize = minCellSize + .5f; }
//Calculate Center Point (usually on Player except when close to the edge)
Vector2f center = new Vector2f(PlayerLocation.X * cellSize, PlayerLocation.Y * cellSize);
/**** NEED HELP HERE ****/
if (center.X < (this.Size.Width / 2) - ((zoneSize * cellSize) / 2)) { center.X = ((zoneSize * cellSize) / 2); }
renderwindow.SetView(new SFML.Graphics.View(center, new Vector2f(this.Size.Width, this.Size.Height)));
}
I believe everything needed to solve this is shown above:
cellSize is the pixel size of each cell
zoneSize is the number of cells (width and height) in each zone
this.Size returns the viewable pixels
cellSize * zoneSize will return the total number of pixels (width and height) that the zone uses.
There is currently a single if statement for adjusting one part center.X and I was planning on doing 3 more. But I can't get that one to work. I've tried several things. Any help would be appreciated.
Coffee kicked in. Here is what I have working:
float totalSize = zoneSize * cellSize;
if (center.X > totalSize - (this.Size.Width / 2))
{
center.X = totalSize - (this.Size.Width / 2);
}
if (center.X < this.Size.Width / 2)
{
center.X = this.Size.Width / 2;
}
if (center.Y > totalSize - (this.Size.Height / 2))
{
center.Y = totalSize - (this.Size.Height / 2);
}
if (center.Y < this.Size.Height / 2)
{
center.Y = this.Size.Height / 2;
}
If anyone can post a better answer (less if statements, more elegant, etc...), that isn't just a rewrite of the above code, withing the next few days, I will be happy to mark that as the answer.
How could I get a random CGPoint that is outside the screen boundaries (frame)?
Also, given that point, how could I find a symmetrical point to it to the middle of the screen- e.g. say I have the point (width+1,height+1). Now the symmetrical point is (-1,-1). Say I have (-1,height +1)- symmetrical would be (width+1,-1).
Hope this is clear, and thanks!
If I understand your question correctly, you can use the following method:
- (CGPoint) randomPointIn:(CGRect)inrect outsideOf:(CGRect)outrect
{
CGPoint p;
do {
p.x = inrect.origin.x + inrect.size.width * (float)arc4random()/(float)UINT32_MAX;
p.y = inrect.origin.y + inrect.size.height * (float)arc4random()/(float)UINT32_MAX;
} while (CGRectContainsPoint(outrect, p));
return p;
}
It returns a random point that is inside inrect, but outside of outrect.
(I have assumed that inrect is "considerably larger" than outrect,
otherwise many loop iterations might be necessary to find a valid point.)
In your case, you would use outrect = CGRectMake(0, 0, width, height),
and inrect would specify the allowed domain.
And the point symmetrical to (x, y) with respect to the middle of the screen
with size (width, height) is (width - x, height - y).
UPDATE: As I just found here: http://openradar.appspot.com/7684419,
CGRectContainsPoint will return false if you provide it a point that is on the boundary of the CGRect. That means that the above method returns a point that is outside of
or on the boundary of the given rectangle outrect. If that is not desired,
additional checks can be added.
I believe this should work.
//To get a random point
- (CGPoint)randomPointOutside:(CGRect)rect
{
// arc4random()%(int)rect.size.width
// This gets a random number within the width of the rectangle
//
// (arc4random()%2) ? rect.size.width : 0)
// This has a 50:50 to put the point in the q1 quadrant relative to the top right point of the rect
//
// q4 q1
// _____ +
// | |
// | q3 | q2
// |_____|
//
float x = arc4random()%(int)rect.size.width + ((arc4random()%2) ? rect.size.width : 0);
float y = arc4random()%(int)rect.size.height + ((arc4random()%2) ? rect.size.height : 0);
return CGPointMake(x, y);
}
//To get the symmetrical point
- (CGPoint)symmetricalPoint:(CGPoint)p around:(CGRect)rect
{
return CGPointMake((p.x-rect.size.width) * -1, (p.y-rect.size.height) * -1);
}
How can I detect when a 2D moving object has crossed its own path?
I store the path as an array of points based on the plane's previous positions.
Pseudo-code or any programming language can be used to describe a solution.
Here's my code I've tried already - it detects a full 360 loop. I think I need a different approach.
CGFloat angleDiff = angleCurr - lastAngleRecorded;
lastAngleRecorded = angleCurr;
// Ensure -180 < angleDiff < 180
angleDiff = angleDiff > M_PI ? angleDiff - (M_PI*2) : angleDiff;
angleDiff = angleDiff < -M_PI ? angleDiff + (M_PI*2) : angleDiff;
// Reset tracking of the loop of the plane's angle exceeds (turns too sharply) or falls below the limits
if(fabsf(angleDiff) < angleDiffMinAllowed || fabsf(angleDiff) > angleDiffMaxAllowed) {
if(++ringFaultCount >= ringFaultCountMax) {
[self resetTracking];
return;
}
}
ringFaultCount = 0;
// Add plane position to ring polygon
[ringPoints addObject:[NSValue valueWithCGPoint: ccp(targetPlane.position.x, targetPlane.position.y)]];
// Add angleDiff to angleTotal
angleTotal += angleDiff;
// Completed loop?
if(fabsf(angleTotal) >= M_PI * 2.f) {
[self resetTracking];
if(isRingJoined){
CCLOG(#"%# RING COMPLETE", NSStringFromSelector(_cmd));
}
return;
}
I also had the problem, I solved it by making a straight line in a coordinate system:
y = mx+q±tolerance
Let me explain:
The line is the tangent of the curve at the point you check if there is a collision this is the line the "aircraft" followed in that point.
The tolerance will make the line move a litlle bit up and also one a little bit down.
so you get 2 parralel lines witch can be seen as boundarys.
you also have to make a tolerance on the x-axis
The m is the direction of the line, its: tan(angle), the angle is the angle with the x-axis.
If all that is setup than you have to do this:
if(y_point < mx+q+tolerance && y_point> mx+q-tolerance && x_points > x-tolerance && x_point< x+tolerance
{
// some code
}