I'm trying to implement simple continuous collision detection for my pong game however i'm not sure i'm implementing or understand this right. AFAIR continuous collision detection is used for fast moving objects that may pass through another object circumventing normal collision detection.
So what I tried was that because the only fast moving object I have is a ball I would just need the position of the ball, its move speed, and the position of the object we are comparing to.
From this I figured it would be best that for example if the ball's move speed indicated it was moving left, I would compare it's left-most bound to the right-most bound of the other object. From this I would step through by adding the move speed to the left-most bound of the ball and compare to make sure it's greater than the other objects right bound. This would show that there is no left right collision.
I have something somewhat working, but unfortunately, the ball starts bouncing normally for a while then it acts as if it hits a paddle when nothing is there.
I'm a bit lost, any help would be appreciated!
static bool CheckContinuousCollision(PActor ball, PRect ballRect, PActor other, PRect otherRect)
{
PVector ballMoveSpeed;
int ballXLimit;
int ballYLimit;
ballMoveSpeed = ball.moveSpeed;
// We are moving left
if ( sgn(ball.moveSpeed.x) < 0 )
{
ballXLimit = std.math.abs(ballMoveSpeed.x) / 2;
for ( int i = 0; i <= ballXLimit; i++ )
{
if ( ballRect.Left < otherRect.Right && otherRect.Left < ballRect.Left)
{
return true;
}
ballRect.Left -= i;
}
}
//We are moving right
if ( sgn(ball.moveSpeed.x) > 0)
{
ballXLimit = std.math.abs(ballMoveSpeed.x) / 2;
for ( int i = 0; i < ballXLimit; i ++ )
{
if ( ballRect.Right > otherRect.Left && ballRect.Right < otherRect.Right )
{
return true;
}
ballRect.Right += i;
}
}
// we are not moving
if ( sgn(ball.moveSpeed.x) == 0)
{
return false;
}
}
You seem to be checking the collision of only one dimension, i.e the X dimension of your ball versus your Other.
What you probably want is to compare whether the two objects collide in 2d space. This can be easily done by adjusting each objects Bounding Rectangle and checking whether the rectangles overlap. Then in your for loop you can adjust your Ball rectangle accordingly
Related
Lets say that on a 2d grid of 20x20, you have your character at position (5,5).
He is able to walk up to 4 tiles in his move. However, there may be obstacles blocking your path such as a wall.
Is there any efficient / easy way for calculating exactly which tiles he would be able to walk to without checking every single possible move ( e.g. move up 0 and right 0 then move up 0 and right 1 e.t.c )?
At the moment I'm calculating the places that you can walk through with this horrific thing:
int playerx = GridPane.getRowIndex(button);
int playery = GridPane.getColumnIndex(button);
int position = playery*8+playerx;
for (int i = 0; i < 5; i++)
{
for (int j = i-4; j < 5-i; j++)
{
try
{
int expectedCollumn = playerx+j;
int actualCollumn = ((position+i+j*8)-((position+i+j*8)%8))/8;
if(expectedCollumn==actualCollumn)
{
Button temp = (Button)gridPane.getChildren()
.get(position+i+j*8);
if (!temp.getText().equals("W") &&
!temp.getText().equals("P"))
{
temp.setText("T");
}
}
actualCollumn = ((position-i+j*8)-((position-i+j*8)%8))/8;
if(expectedCollumn==actualCollumn)
{
Button temp2 = (Button)
gridPane.getChildren().get(position-i+j*8);
if (!temp2.getText().equals("W") &&
!temp2.getText().equals("P"))
{
temp2.setText("T");
}
}
}
}
}
However, its showing as if you are able to walk to the otherside of the wall and I'm not sure how I would go about fixing this.
Many thanks in advance.
For path finding, you should figure out how this works:
https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
and then move on to A* or something more efficient.
Thanks to everyone that answered but the solution was simple
incase somehow someone finds this post and is interested it was a simple recursive call
void getReachableTiles(Tile current, Int stamina, List<Tile> visited, List<Tile> reachable) {
if (stamina <= 0) return;
List<Tile> neighbours = new List<>(current + up, current + left, ..)
for (Tile t in neighbours) {
if (!visited.contains(t)) {
visited.append(t);
if (!t.isWall()) {
reachable.append(t);
getReachableTiles(t, stamina - 1, visited, reachable);
}
}
}
}
I am make a game for school, within this game I have an (hero)asset, this asset walks on keypresses and stops when I don't press the key.
The only problem I have, is when the I stop walking de animation keeps on running. In other words, it stands still, but it still walks.
This is my code:
/////////////////////
// MOVING //
/////////////////////
if(keyboard_check(vk_left)){ // moving left collisions
dir=-1; // set the correct direction
image_xscale = dir; // make the sprite face the correct direction
// if we are not jumping or falling
sprite_index = spr_denpman_Loop; // set the sprite to walking
x=x-xspeed // move the player left
c2 = -1;
c3 = -1;
// check the points at the bottom of the sprite
c1 = tilemap_get_at_pixel(obj_Spel.map,x-(sprite_get_width(sprite_index)/2),y-1); // left
c3 = tilemap_get_at_pixel(obj_Spel.map,x,y-1); // center
if( y&$3f>0 ) c2=tilemap_get_at_pixel(obj_Spel.map,x-(sprite_get_width(sprite_index)/2),y+1); // left below (only check if there is a tile below)
if(c1 == 3) || (c2 == 3){ // if we are intersecting with a box
x = real(x&$ffffffc0)+(sprite_get_width(sprite_index)/2); // stop the player from moving
}
if(x < 0){ // the the player has moved off the edge of the screen
x = room_width; // wrap around to the other side of the screen
}
}else if(keyboard_check(vk_right)){ // moving right collisions (check with else so that both directions cant be triggered at the same time)
dir=1; // set the correct direction
image_xscale = dir; // make the sprte face the correct direction
// if we are not jumping or falling
sprite_index = spr_denpman_Loop; // set the sprite to walking
image_speed = anim_speed;
x=x+xspeed; // move the player right
c2 = -1;
c3 = -1;
// check the points at the bottom of the sprite
c1 = tilemap_get_at_pixel(obj_Spel.map,x+(sprite_get_width(sprite_index)/2),y-1); // right
c3 = tilemap_get_at_pixel(obj_Spel.map,x,y-1); // center
if( y&$3f>0 ) c2=tilemap_get_at_pixel(obj_Spel.map,x+(sprite_get_width(sprite_index)/2),y+1); // right below (only check if there is a tile below)
if(c1 == 3) || (c2 == 3){ // if we are intersecting with a box
x = real(x&$ffffffc0)+obj_Spel.tilesize-(sprite_get_width(sprite_index)/2); // stop the player from moving
}
if(x > room_width){ // the the player has moved off the edge of the screen
x = 0; // wrap around to the other side of the screen
}
}
It's pretty simple, the sprite will remain at the walking sprite because that's the last sprite you've given a command to changes into.
You also need to make a command to show the standing sprite for when it stops walking.
Place this at the end of your if-else-statement:
else
{
sprite_index = spr_denpman_Loop; //stops the player if there's no key pressed.
}
(And replace the spr_denpman_Loop with the name of your standing sprite)
And on a sidenote, please look at your own code and understand what you're reading as well. I know the demo you're using, and that only explains the very basics of the program, I can't recommend using that as a base for a game. Since a lot of code can be simplified.
I have been implementing various forms of simple collision detection with varying results. I have a fairly good working version of collision detection, but there are some odd behaviors that I can't work out.
Just for a reference, i'm making a simple pong game, and trying to refine the collision. The problems I get are when the ball collides with the paddle on either the top or bottom side. In those cases, the ball hovers above (or below) the paddle and does not move. I'm guessing this is because of how i'm checking for collision and how i'm altering the movespeed of the ball.
I would like to implement a way I differentiate between top/bottom and left/right collision but this is the only method that works decently:
static void CheckCollision(PActor object1, PActor object2, PInput pinput)
{
if ( CheckObjectCollision( object1, object2 ) )
{
AdjustMoveSpeed( object1, object2, pinput );
}
}
static bool CheckObjectCollision(PActor object1, PActor object2)
{
int object1LeftBound = object1.position.x;
int object1RightBound = object1.position.x + object1.actorTextureXSize;
int object1TopBound = object1.position.y;
int object1BottomBound = object1.position.y + object1.actorTextureYSize;
int object2LeftBound = object2.position.x;
int object2RightBound = object2.position.x + object1.actorTextureXSize;
int object2TopBound = object2.position.y;
int object2BottomBound = object2.position.y + object2.actorTextureYSize;
if ( object1RightBound < object2LeftBound )
return false;
if ( object1LeftBound > object2RightBound )
return false;
if ( object1BottomBound < object2TopBound )
return false;
if ( object1TopBound > object2BottomBound )
return false;
return true;
}
I am guessing that the root of some of the problems i'm having is the function AdjustMoveSpeed, here it is:
static void AdjustMoveSpeed(PActor object1, PActor object2, PInput pinput)
{
PVector prevMouseLocation = pinput.GetPrevMouseLocation();
PVector currMouseLocation = pinput.GetCurrMouseLocation();
int currentMoveSpeed;
int nextMoveSpeed;
if (typeid(object1) == typeid(PBall))
{
object1.moveSpeed.x *= -1;
if ( typeid(object2) == typeid(PPlayer) )
{
currentMoveSpeed = object1.moveSpeed.y;
nextMoveSpeed = prevMouseLocation.y - currMouseLocation.y;
object1.moveSpeed.y = (prevMouseLocation.y - currMouseLocation.y) * -1;
}
else
{
if (object1.moveSpeed.y > 0)
object1.moveSpeed.y *= -1;
}
}
else if (typeid(object2) == typeid(PBall))
{
object2.moveSpeed.x *= -1;
if ( typeid(object1) == typeid(PPlayer) )
{
currentMoveSpeed = object1.moveSpeed.y;
nextMoveSpeed = prevMouseLocation.y - currMouseLocation.y;
object2.moveSpeed.y = (prevMouseLocation.y - currMouseLocation.y) * -1;
}
else
{
if (object2.moveSpeed.y > 0)
object2.moveSpeed.y *= -1;
}
}
}
What I was attempting to do with AdjustMoveSpeed, is first check to see which object is the ball, after this, multiply the x move speed by -1 to reverse its direction. After this, I check to see if the other object is a player, if so I set the y move speed to the difference between the previous mouse location and current mouse location. This is here to give the player option to change the balls y speed, or add spin.
I've tried checking for intersection between objects so that I can get a specific side, and the result is the ball just flying in the middle of the screen without actually hitting either paddle.
How do I properly check for collision detection on two objects that are squares?
How can I fix AdjustMoveSpeed so that it works properly with collision detection?
Lastly, how do I keep the momentum of the ball of its current speed is greater than the difference of the mouse location before and after the hit?
I've tried taking comparing the absolute value of currentMoveSpeed and nextMoveSpeed but then the ball doesn't change y speed. Something like this:
if ( abs(currentMoveSpeed) < abs(nextMoveSpeed )
object1.moveSpeed.y = (prevMouseLocation.y - currMouseLocation.y) * -1;
else
object1.moveSpeed.y *= -1
Pong is simple enough that, rather than moving the ball each frame and checking for a collision with a paddle, you can actually solve the equation for when the paddle and ball will collide - if that time is less than one frame, there is a collision.
This completely eliminates the issue of the ball moving so fast it moves through the paddle, an issue that plagues many pong-clones that use the naive method of collision-detection.
This solution is called continuous collision detection - see this answer for more information.
If the ball gets stuck on the paddle instead of bouncing it is probably because it keeps changing direction back and forth. The ball should only bounce if it is heading towards the paddle.
if (sgn(object1.moveSpeed.x) == sgn(object1.x - object2.x)) {
// Ball is already moving away from the paddle, don't bounce!
}
else {
// Ok to bounce!
object1.moveSpeed.x *= -1;
}
I created this function to move a unit along way points that are saved in list_. Every Unit has its own list_. move() is initially called with the speed (distance/step) every step. Then depending on the distance to the next way point three possible actions are taken.
Can you suggest any improvements?
void Unit::move(qreal maxDistance)
{
// Construct a line that goes from current position to next waypoint
QLineF line = QLineF(pos(), list_.firstElement().toPointF());
// Calculate the part of this line that can be "walked" during this step.
qreal part = maxDistance / line.length();
// This step's distance is exactly the distance to next waypoint.
if (part == 1) {
moveBy(line.dx(), line.dy());
path_.removeFirst();
}
// This step's distance is bigger than the distance to the next waypoint.
// So we can continue from next waypoint in this step.
else if (part > 1)
{
moveBy(line.dx() , line.dy());
path_.removeFirst();
if (!path_.isEmpty())
{
move(maxDistance - line.length());
}
}
// This step's distance is not enough to reach next waypoint.
// Walk the appropriate part of the length.
else /* part < 1 */
{
moveBy(line.dx() * part, line.dy() * part);
}
}
I'll hate myself for suggesting a deprecated way of doing things, but there's no reference to the replacing method :(
QGraphicsItemAnimation
It has addStep and linear interpolation stuff as a convenience.
It seems Qt devs would like you to use QTimeLine itself as a replacement.
I'd use Qt Animation Framework, more precisely QPropertyAnimation:
// I use QPainterPath to calculate the % of whole route at each waypoint.
QVector<qreal> lengths;
QPainterPath path;
path.moveTo(list_.first());
lengths.append(0);
foreach (const QPointF &waypoint, list_.mid(1)) {
path.lineTo(waypoint);
lengths.append(path.length());
}
// KeyValues is typedef for QVector< QPair<qreal, QVariant> >
KeyValues animationKeyValues;
for (int i(0); i != lenghts.count(); ++i) {
animationKeyValues.append(qMakePair(path.percentAtLength(lenghts.at(i)), list_.at(i)));
}
// I assume unit is a pointer to a QObject deriving Unit instance and that
// Unit has QPointF "position" property
QPropertyAnimation unitAnimation(unit, "position");
unitAnimation.setKeyValues(animationKeyValues);
unitAnimation.setDuration(/* enter desired number here */);
unitAnimation.start();
I haven't tested this solution, but you should get the general idea.
I render isosurfaces with marching cubes, (or perhaps marching squares as this is 2D) and I want to do set operations like set difference, intersection and union. I thought this was easy to implement, by simply choosing between two vertex scalars from two different implicit surfaces, but it is not.
For my initial testing, I tried with two spheres circles, and the set operation difference. i.e A - B. One circle is moving and the other one is stationary. Here's the approach I tried when picking vertex scalars and when classifying corner vertices as inside or outside. The code is written in C++. OpenGL is used for rendering, but that's not important. Normal rendering without any CSG operations does give the expected result.
void march(const vec2& cmin, //min x and y for the grid cell
const vec2& cmax, //max x and y for the grid cell
std::vector<vec2>& tri,
float iso,
float (*cmp1)(const vec2&), //distance from stationary circle
float (*cmp2)(const vec2&) //distance from moving circle
)
{
unsigned int squareindex = 0;
float scalar[4];
vec2 verts[8];
/* initial setup of the grid cell */
verts[0] = vec2(cmax.x, cmax.y);
verts[2] = vec2(cmin.x, cmax.y);
verts[4] = vec2(cmin.x, cmin.y);
verts[6] = vec2(cmax.x, cmin.y);
float s1,s2;
/**********************************
********For-loop of interest******
*******Set difference between ****
*******two implicit surfaces******
**********************************/
for(int i=0,j=0; i<4; ++i, j+=2){
s1 = cmp1(verts[j]);
s2 = cmp2(verts[j]);
if((s1 < iso)){ //if inside circle1
if((s2 < iso)){ //if inside circle2
scalar[i] = s2; //then set the scalar to the moving circle
} else {
scalar[i] = s1; //only inside circle1
squareindex |= (1<<i); //mark as inside
}
}
else {
scalar[i] = s1; //inside neither circle
}
}
if(squareindex == 0)
return;
/* Usual interpolation between edge points to compute
the new intersection points */
verts[1] = mix(iso, verts[0], verts[2], scalar[0], scalar[1]);
verts[3] = mix(iso, verts[2], verts[4], scalar[1], scalar[2]);
verts[5] = mix(iso, verts[4], verts[6], scalar[2], scalar[3]);
verts[7] = mix(iso, verts[6], verts[0], scalar[3], scalar[0]);
for(int i=0; i<10; ++i){ //10 = maxmimum 3 triangles, + one end token
int index = triTable[squareindex][i]; //look up our indices for triangulation
if(index == -1)
break;
tri.push_back(verts[index]);
}
}
This gives me weird jaggies:
(source: mechcore.net)
It looks like the CSG operation is done without interpolation. It just "discards" the whole triangle. Do I need to interpolate in some other way, or combine the vertex scalar values? I'd love some help with this.
A full testcase can be downloaded HERE
EDIT: Basically, my implementation of marching squares works fine. It is my scalar field which is broken, and I wonder what the correct way would look like. Preferably I'm looking for a general approach to implement the three set operations I discussed above, for the usual primitives (circle, rectangle/square, plane)
EDIT 2: Here are some new images after implementing the answerer's whitepaper:
1.Difference
2.Intersection
3.Union
EDIT 3: I implemented this in 3D too, with proper shading/lighting:
1.Difference between a greater sphere and a smaller sphere
2.Difference between a greater sphere and a smaller sphere in the center, clipped by two planes on both sides, and then union with a sphere in the center.
3.Union between two cylinders.
This is not how you mix the scalar fields. Your scalars say one thing, but your flags whether you are inside or not say another. First merge the fields, then render as if you were doing a single compound object:
for(int i=0,j=0; i<4; ++i, j+=2){
s1 = cmp1(verts[j]);
s2 = cmp2(verts[j]);
s = max(s1, iso-s2); // This is the secret sauce
if(s < iso) { // inside circle1, but not inside circle2
squareindex |= (1<<i);
}
scalar[i] = s;
}
This article might be helpful: Combining CSG modeling with soft blending using
Lipschitz-based implicit surfaces.