I am trying to develop basic enemy AI on a simple platformer game after following Shaun Spalding's gamemaker 2 platformer tutorials on youtube. My code is the exact same as his on the tutorial but for some reason, when my enemy detects collision with the wall he turns around as he is suppose to and then detects another collision where there is none, causing him to turn around again.
This is my code:
// Horizontal collision
if (place_meeting(x+hsp, y, oWall)) {
show_debug_message(hsp)
while (!place_meeting(x+sign(hsp), y, oWall)) {
x += sign(hsp); // slows down I think
}
hsp = -hsp;
}
x += hsp;
The -hsp part is where he turns around. Somehow, he is detecting another collision as soon as he does so, even though the value of hsp is inverted. Can anyone possibly point me in the direction of why this may be occuring?
(Value of hsp initialized at 3 and never changed only for inversion).
Is it turning back to the wall after a short while, or is it stuck and is flickering to left and right rapidly? Both could involve that the collision point isn't updating well.
When I face with collision problems, I'll use a crosshair sprite, and draw it at the same position as where it should be colliding. that way I've a visible view of the 'collision point'.
Another cause could be the sprite's origin point, that determines at which position the x and y appears, and that the sprite by turning collides with the wall itself. Keep in mind that the origin point is at the center of it's collision mask, to avoid been stuck in a wall.
EDIT: Another possibility: the collision point still checks inside the sprite.
For that, you could also try using an offset that keeps the collision point away from the sprite collision, but to let that work, you'll need to keep the inverse direction away from your horizontal speed. Something like this:
// Horizontal collision
_offset = 15; //moves the collision point away to check in front of the sprite. value depends on the size of the sprite.
_dir = 1; //the direction, should only be 1 or -1
//hsp should no longer be used to inverse, use a new variable (like _dir) instead
collisionPoint = (hsp + offset) * _dir;
if (place_meeting(x + collisionPoint , y, oWall)) {
show_debug_message(collisionPoint)
while (!place_meeting(x+sign(collisionPoint), y, oWall)) {
x += sign(collisionPoint); // slows down I think
}
_dir = -_dir
}
x += hsp * _dir;
Related
I am coming back since I am having this geometric problem that I am not familiar with on Unity.
For a f-zero style game, I have a collider box (white on the screen captures) which is the origin of my raycast, and is bound to the movement of the vehicle.
In the shown code, this is this.collider. I control its rotation via a traditional applymatrix and there is no problem.
Then, on top of that, I have the rendered body of the vehicle in this.meshes. It inherits the rotation of the collider box, but gets some extra rotation on its vertical axis to give a visual sliding dynamic during the hard turns.
It is separate from the collider to keep the vector.forward of the movement (and the raycast) not affected by the extra-rotation. This is purely visual.
My question is: what is the best way to implement it?
I tried different things, but, basically, if I copy the position and rotation of the collider, no problem. As soon as I try to add some extra rotation = this.driftRotation, my body flips when rotation.y value is less than -math.pi. I can adjust the value of the rotation by incrementing Math.PI (like in Unity), but it doesn't work here.
No clean solution found with applyMatrix neither, and not a lot of google answers on "vertical rotation flip mesh"... though I'm pretty sure this pissue is common.
Some code:
this.meshes.position.set(
this.collider.position.x,
this.collider.position.y,
this.collider.position.z);
this.meshes.rotation.x = this.collider.rotation.x;
this.meshes.rotation.y = this.collider.rotation.y + this.driftRotation;
this.meshes.rotation.z = this.collider.rotation.z;
Enclosed more explicit pictures:
Thank you
Marquizzo, that's precisely the point: the 3rd px follows the 2nd one, so I'm still turning right but rotation suddenly flips (again, when rotation.y reaches -PI).
Anyway, I fixed it by not trying to directly change rotation.y value, but playing with matrix. Just takes time to understand what does what.
For those who may face a similar pb, here is my temp solution, until I find sthing more performant:
this.meshes.matrix.identity();
if (Math.abs(driftAmount) > 0)
{
this.driftAxis.copy(this.driftDirection);
this.driftValue = js.Utils.lerp(this.driftValue, Math.sign(driftAmount) * 0.4, 0.05);
this.meshes.matrix.makeRotationAxis(this.driftAxis, this.driftValue);
}
else if (Math.abs(this.driftValue) > 0)
{
this.driftAxis.copy(this.driftDirection);
this.driftValue = js.Utils.lerp(this.driftValue, 0, 0.1);
if (Math.abs(this.driftValue) < 0.001)
{
this.driftValue = 0;
}
this.meshes.matrix.makeRotationAxis(this.driftAxis, this.driftValue);
}
this.meshes.applyMatrix(this.collider.matrix);
I had to add a driftAxis along a driftDrection, which is my axis for my vertical rotation.
For ref. I think this subject is +/- bound to the issue I had:
https://github.com/mrdoob/three.js/issues/1460
Now I have another issue, how to add another rotation to this.meshes on another axis, the forward one, for a rolling effect, because if I just add another makeRotationAxis in this code it just skips the first one. But that sounds less difficult to figure out, there must exist the equivalent of combineMatrix something...
I think this is ultimately a pretty simple question, but it's hard to describe, thus, I provide a working example here (in the sample press 'z' to see rotation with unwanted translation and 'x' keys to rotate with a compensating re-position).
Basically, I am trying to rotate an object (a thumbstick) about the z-axis of a complex model loaded via gltf (a model of the oculus rift touch controller). It's easy to rotate about the x-axis because it's 90 deg. orthogonal to the x-axis. About the z-axis, it's harder because the plane the thumbstick is attached to is angled at 30 deg. I realize that if the thumbstick were using local coordinates, this wouldn't be a problem, but 'thumb.rotation.z' does not seem to be using local coordinates and is rotating about the model's (as a whole), or maybe even the scene's global y and z (?). Anyway, after a bunch of futzing around, I was able to get things to work by doing the following:
// occulus plane is angle at 30 deg, which corresponds to
// 5 units forward to 3 units down.
var axis = new THREE.Vector3(0, 5, -3).normalize();
factory.thumbstick.geometry.center();
var dir = (evt.key === 'x' ? 1 : -1);
thumb.rotateOnAxis(axis, factory.ONE_DEG * 5.0 * dir);
Basically, I'm rotating about a "tilted" axis, and then calling 'center' to make thumbstick centered on the pivot point, so it rotates about the pivot point, rather than around the pivot point (like the earth orbiting the sun).
Only problem is that when you call 'geometry.center()' and then call 'rotateOnAxis', it translates the thumbstick to the pivot point:
Note: the position on the thumbstick object is (0,0,0) before and after the calls.
I have empirically determined that if I alter the position of the thumbstick after the translation like so:
// magic numbers compensating position
var zDisp = 0.0475;
var yDisp = zDisp / 6.0
thumb.position.x = 0.001;
thumb.position.y = -yDisp;
thumb.position.z = zDisp;
Then it (almost) returns back to it's original position:
Problem is these numbers were just determined by interactively and repeatedly trying to re-position the thumbstick i.e. empirically. I simply cannot find a programmatic, analytical, api kind of way to restore the original position. Note: saving the original position doesn't work, because it's zero before and after the translation. Some of the things I tried were taking the difference between the bounding spheres of the global object and the thumbstick object, trying to come up with some 'sin x- cos x' relation on one distance etc. but nothing works.
My question is, how can I progammatically reverse the offset due to calling 'geometry.center()' and rotateOnAxis (which translates to the pivot point), without having to resort to hacked, empircal "magic" numbers, that could conceivably change if the gltf model changes.
Of course, if someone can also come up with a better way to achieve this rotation, that would be great too.
What's throwing me is the (peceived?) complexity of the gltf model itself. It's confusing because I have a hard time interpreting it and it's various parts: I'm really not sure where the "center" is, and in certain cases, it appears with the 'THREE.AxesHelper' I'm attaching that what it shows as 'y' is actually 'z' and sometimes 'up' is really 'down' etc, and it gets confusing fast.
Any help would be appreciated.
The breakthrough for me on this was to re-frame the problem as how do I change the pivot point for the thumbstick, rather than how do I move the thumbstick to the (default and pre-existing) pivot point. To paraphrase JFK, "ask not how you can move to the pivot, but ask how the pivot can move to you" :-)
After changing my angle of attack, I pretty quickly found the aforementioned link, which yielded my solution.
I posted an updated glitch here, so now pressing z works as I expected. Here is the relevant code portion:
factory.onModelLoaded = function(evt) {
console.log(`onModelLoaded: entered`);
factory.thumbstick = this.scene.children[1].children[2]
let thumb = factory.thumbstick;
// make the thumb red so it's easier to see
thumb.material = (new THREE.MeshBasicMaterial({color: 0xFF7777}));
// use method from https://stackoverflow.com/questions/28848863/threejs-how-to-rotate-around-objects-own-center-instead-of-world-center/28860849#28860849
// to translate the pivot point of the thumbstick to the the thumbstick center
factory.thumbParent = thumb.parent;
let thumbParent = factory.thumbParent;
thumbParent.remove(thumb);
var box = new THREE.Box3().setFromObject( thumb );
box.getCenter( thumb.position ); // this basically yields my prev. "magic numbers"
// thumb.position.multiplyScalar( - 1 );
var pivot = new THREE.Group();
thumbParent.add( pivot );
pivot.add( thumb );
thumb.geometry.center();
// add axeshelp after centering, otherwise the axes help, as a child of thumb,
// will increase the bounding box of thumb, and positioning will be wrong.
axesHelper = new THREE.AxesHelper();
thumb.add(axesHelper);
}
Which allows my "z" handler to just rotate without having to do translation:
case 'z':
case 'Z':
var axis = new THREE.Vector3(0, 5, -3).normalize();
var dir = (evt.key === 'z' ? 1 : -1);
thumb.rotateOnAxis(axis, factory.ONE_DEG * 5.0 * dir);
break;
Interestingly, it's the call to box.getCenter() that generates numbers very close to my "magic numbers":
box.getCenter()
Vector3 {x: 0.001487499801442027, y: -0.007357006114165027, z: 0.04779449797522323}
My empirical guess was {x: 0.001, y: -0.00791666666, z: 0.0475} which is %error {x: 32.7%, y: 7.6%, z: 0.61%}, so I was pretty close esp. on the z component, but still not the "perfect" numbers of box.getCenter().
I am trying to implement background scrolling using SDL 2.
As far as I understand one can only move source rectangle by an integer value.
My scrolling works fine when I move it by one every iteration of the game loop.
But I want to move it slower. I tried to move it using this code
moved += speed;
if (moved >= 1.0) {
++src_rect.x;
moved -= 1;
}
Here moved and speed are doubles . I want my background to move something like ten times slower, therefore I set speed to 0.1. It does move ten times slower, but the animation is no longer smooth. It kind of jumps from one pixel to another, which looks and feels ugly when the speed is low.
I am thinking of making my background larger and scrolling it using an integer. Maybe when background is large enough the speed of 1 will seem slower.
Is there a way to scroll not a very large background slowly and smoothly and the same time?
Thanks.
What I would do is have a set of floats that would track the virtual screen position, then you just cast the floats to integers when you actually render, that way you don't ever lose the precision of the floats.
To give you an example, I have an SDL_Rect, I want to move it every frame. I have two floating point variables that track the x and y position of the rect, every frame I would update those x and y positions, cast them to an integer, and then render the rect, EX:
// Rect position
float XPos = 0.0f;
float YPos = 0.0f;
SDL_Rect rect = {0, 0, 64, 64};
// Update virtual positions
XPos += 20.0f * DeltaTime;
YPos += 20.0f * DeltaTime;
// Move rect down and to the right
rect.x = (int)XPos;
rect.y = (int)YPos;
While this doesn't give you the exact result you are wanting, it is the only way that I know of to do this, it will let you delay your movement more precisely without giving you that ugly chunkiness in the movement, it also will let you add stuff like more precise acceleration too. Hope this helps.
What is the proper way to add a sphere constraint to a cloth sim?
I am trying to add a sphere (or capsule) constraing to Skeel Lee's cloth simulation source code, but I am not sure how to do it properly.
I created a rather simple constraint which "kicks" the particle back out of the sphere in the opposite direction (opposite from the vector towards the center):
void SatisfySphereConstraints()
{
foreach (var simObj in this.simObjects)
simObj.CurrPosition += SphereConstraint(simObj.CurrPosition, _center, _radius);
}
Vector3 SphereConstraint(Vector3 position, Vector3 center, float radius)
{
var delta = position - center;
var distance = delta.Length();
if (distance < radius)
return (radius - distance) * delta / distance;
return Vector3.Zero;
}
And then I inserted the method in the existing code:
ApplyForces();
Integrate();
for (var i = 0; i < constraintIterations; i++)
{
foreach (Constraint constraint in constraints)
constraint.SatisfyConstraint();
SatisfySphereConstraints(); // <-- I added it here
}
The collision code works fairly well for situations like this (C is the center of the sphere, P is the current particle position, P' is the resolved position):
But the problem occurs if particles are moving very quickly, because then the particle basically jumps to the other side of the sphere (P1 is the previous position, P2 is the current position, P' is how I think it should be resolved), instead of returning back to the previous position:
Since this is a cloth simulation, the cloth basically jumps over the sphere in that case, instead of being "stopped" by the sphere.
Now, I could try to return in the direction of the previous point, but since the sphere might also be moving, I am not sure if P1 is even a valid position (and if it will make sense). Also, it seems to be more computationally expensive - is this how I am supposed to do it, or not?
Cloth like things snapping to the wrong side of an obstacle and getting stuck there is not too uncommon. Even more common is fast moving objects overlapping way too much when the collision is detected.
A common solution is, on detecting a collision, sub divide the previous step until the collision is less severe and then resolve it. I think you will find trying to detect how deep the collision is to be difficult in your case, but if you could limit the top speed of spheres in your system you could binary split the frames in which collisions occur a fixed number of times and assume it will be good enough?
if (it collides at time T and didn't at T-1)
if (it collides at T-0.5)
try T-0.75
else
try T-0.25
etc...
Are you prepared to accept that it will sometimes be wrong, or does it have to be always a good result?
I've searched far and wide, so if there's a similar question please forgive me but I just couldn't find it.
To put what I'm trying to do in context: I want to create an infinitely-generated field of stars that disappear as they go offscreen and reappear at the edge of the screen where the camera is moving. I'm working with a top-down view, so it must be pretty simple to achieve this, but alas I haven't a clue.
I'm using the following code to determine whether a star has gone off-screen and then replace it:
//update camera frustum
camera.projScreenMatrix.multiplyMatrices(
camera.projectionMatrix,
camera.matrixWorldInverse
);
camera.frustum.setFromMatrix(camera.projScreenMatrix);
//loop through stars
var stars=scene.stars.geometry.vertices;
for(var i=0;i<stars.length;i++) {
if(!camera.frustum.containsPoint(stars[i])) {
stars[i]=new THREE.Vector3(
// fill in the blank
);
scene.stars.geometry.verticesNeedUpdate=true;
}
}
Since I'm using a perspective camera, I know I'll need to somehow factor in camera.fov and other perspective elements, but as you can tell I'm no expert on the third dimension.
Assuming I have an angle or normalized vector telling me the direction the view is panning, how would I go about creating a vertex along the edge of the screen regardless of its Z position?
If I'm not clear enough, I'll be happy to clarify. Thanks.
I know this is an old question, but I came across it while looking for an answer and found a simple, trigonometry reliant method to get the left edge of the camera frustum, and I'm sharing it in case someone else might find it useful:
// Get half of the cameras field of view angle in radians
var fov = camera.fov / 180 * Math.PI / 2;
// Get the adjacent to calculate the opposite
// This assumes you are looking at the scene
var adjacent = camera.position.distanceTo( scene.position );
// Use trig to get the leftmost point (tangent = o / a)
var left = Math.tan( fov ) * adjacent * camera.aspect;
Basically, this gets the leftmost point, but if you don't multiply by the aspect ratio you should get a point in a circle around your camera frustum, so you could translate a point any direction away from the cameras focus and it would always be outside the frustum.
It works by assuming that the imaginary plane that is the camera is perpendicular to the line connecting the camera and its focus, so there is a straight angle. This should work if you want objects further away as well (so if you want them at a further point from the camera you just need to increase the distance between the focus and the camera).
Well, countless headaches and another question later, I've come up with a fairly makeshift answer. Just in case by some unlikely chance someone else has the same question, the following function plots a point on the scene relative to the camera's current view with whatever Z specified:
//only needs to be defined once
var projector=new THREE.Projector();
//input THREE.Vector3
function(vector) {
var z=vector.z;
vector.z=0;
projector.unprojectVector(vector,camera);
return camera.position.clone().add(
vector
.sub(camera.position)
.normalize()
.multiplyScalar(
-(camera.position.z-z)/vector.z
)
);
The x and y, in this case, both range from -1 to 1 for bottom-left to top-right. You can use position/window.Width and position/window.Height for extra precision (using mouse coordinates or what have you).