# Questions tagged [geometry]

A branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space.

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### Get vertices of a terrain mesh affected by a brush or placement shape

I have the following mesh, it has very simple structure. You can think of it as a terrain from top-down view: each vertex (red and numbered) is a fixed distance away from its four neighbours in the ...
35 views

### Finding equivalent axial coordinates for a wrapping hexagonal map of radius n

I'm creating a wrap around hexagonal map that will potentially render infinatly. With the method I'm using, I have an x-y coordinate I use to find it's equivalent axial coordinate with the equations:...
17 views

### Intersection of ray and non-axis-aligned box

I need to compute the intersection of a ray with a non-axis aligned box. Currently, I transform the ray into the local space of the box, do classic ray-AABB intersection and transform the intersection ...
61 views

### Push cube outside triangle face

I'm creating a 3D game, and I need to know how to push a player (axis aligned box/cube) outside a triangle. How can I get get the push direction?
125 views

### How can I detect whether a point is moving in a circle?

I want to detect if my GameObject (Vector3 Point) being dragged by the player's finger is moving in a circular fashion. I thought I could save the last 5 points ...
38 views

### Find optimal placement for label/sticker on a simple polygon with holes

I'm working on a real-time archviz renderer and I need to place a label/sticker/decal on walls, which have openings. So one way to think about this is a simple (possibly concave) polygon with holes. ...
2k views

### How to rotate a local position offset based on a direction vector?

I'm trying to fire three raycasts in the direction of movement, from offset starting points. I'm having trouble calculating the start positions of the rays based on the direction. As you can see in ...
24 views

### Finding the line segments where 2 polygons share an edge

I am working on code to place doors between rooms on my levels. Rooms are lists of points which make up a polygon. In order to find a place for a door between two rooms, I need to find what line ...
368 views

### Shrink a convex polygon

Shrinking a concave polygon is quite hard, to do well. But I expect shrinking a convex polygon would be easy. The naive approach of moving each vertex a certain distance to the centre gives me poor ...
284 views

### Background made with procedural shapes

I would like to know how to make a background like Super Hexagon managed to do: a hexagon in the middle and equally sized trapezoids. There's a screenshot below & the here is the effect in motion....
33 views

### Unprojeting a line on the screen

I have a line connecting two points of my model. I see a projection of this line on my screen and a want to map a point of that projection to the corresponding point in my model PoV. Let ...
81 views

### Detect walls in geometry

Is it possible to automatically detect walls in polygon soup? Of course it's hard to strictly define what a wall is, my slightly vague definition would be: A wall is a largest possible box (not ...
27 views

### How to properly space train bogies

I have a small project with a train that follows a track, composed of discrete pieces. For each piece I calculate the location based on distance traveled, and each carriage gets a fixed offset. I ...
28 views

### Algoritm for scaling an 3D model with fixed edges

I am looking for an algorithm that allows me to scale a 3D model with certain fixed edges. For example scaling up a window should have the frame remain a fixed width while the length of the frame ...
32 views

### Finding rotation quaternion from orthonormal basis?

Given three 3D unit vectors $a$, $b$, $c$ such that: $a \times b = c$ $b \times c = a$ $c \times a = b$ (ie $a, b, c$ form an orthonormal basis) How do we calculate a unit ...
434 views

### Overlap color between objects

I'm currently trying to build a game with Ogre3D that is basically a moving vehicle that leaves a green trail (2D manual mesh) in it's path, what i'm trying to achieve is exactly what this image shows:...
31 views

### Finding Endpoint of line in Unity

I have a startpoint, magnitude(length) and direction and want to find endpoint to construct the line here is the code to make question more clear ...
24 views

### Figuring out the exponent in a spotlight equation from the angle of a cone

I followed a tutorial on how to build a spotlight using DirectX. This tutorial uses a point light equation plus a line of code to limit the light to the shape of a cone. I have everything working, but ...
39 views

### How to calculate plane corner vertices from plane origin point and plane normal?

I have an origin point, and normal vector of a 3D plane. I want to calculate 4 vertices to use as the corners of a 2 triangle quad to render the plane.
52 views

### Calcluate Mesh top, bottom, left and right position relative to mouse click position on the mesh

I have a mesh (suppose it can be circle, or rectangular,square or an arc). The geometry of the mesh can be anything. I can click on mesh at any position. From relative to the clicked position, I want ...
1k views

### Repairing back-facing triangles without user input

My 3D application works with user-imported 3D models. Frequently, those models have a few vertices facing into the wrong direction. (For example, there is a 3D roof and a few triangles of that roof ...
2k views

### Textureing subdivided Icosahedron in XNA, seam problem

*****Look below for the updated source code*** I have started to to make some different types of objects and create them by code in XNA. Right now I have finished the code for creating a Icosahedron. ...
64 views

### Draw a line along one continuous edge of a curved mesh

I have a rectangular mesh, but the mesh is curved: I want to draw a line along one side of this curvy mesh. Currently I can easily draw line along a side of a flat rectangular mesh by getting the ...
49 views

### Tube model imported from Blender getting stretched vertically when rendering

I'm actually working on a 3D game engine with OpenGL 4 and C++. The problem is that, I don't know why, my geometry isn't well renderered except for primitives. At the right you can see a cube, it is ...
53 views

### Pong paddle and deflection angles

I'm trying to make a pong clone and am having trouble grasping ball deflection. The way I'm approaching it is to increase the angle by how far the ball collides from the middle of the paddle. However, ...
91 views

### How do make a box collider align with a line renderer continuously?

I am having the issue of aligning my BoxCollider2D with my linerenderer. I am trying to have a laser shoot using: ...
20 views

### Tilemap Collision Generation - Tracing Polygons with Slopes

I've been using Godot for my game, but it has a unfortunate quirks with tilemap collision where physics objects can bounce weirdly near tile seams and kinematic bodies can often get stuck in seams as ...
8k views

### Sphere-Sphere intersection and Circle-Sphere intersection

I have code for circle-circle intersection. But I need to expand it to 3-D. How do I calculate: Radius and center of the intersection circle of two spheres Points of the intersection of a sphere and ...
2k views

### Converting between Spiral Honeycomb Mosaic and axial hex coordinates

There seems to be quite a lot of logic in dealing with hexagonal grids using a system of axial coordinates like the one described here. In doing some reading about hex grids, though, I ran across the ...
54 views

### High speed collision detection using separating axis theorem

I’m using the SAT and the minimum translation vector from it to detect and handle collision in my 2D game. It works great for regular speeds, (i.e. when the speed is low enough so that an object doesn’...
59 views

### how can I transform a skewed line to a vertical line?

So, I have a line: And I skewed it with x += y * cos(angle) and got something like: My question is, if I have another line segment with that same skew, how can I ...
895 views

### rotating an object from sourceAngle to destAngle, both 0-359, clockwise or counter clockwise?

I've got a game object i need to rotate. It's current angle is player.rotation, the destination is targetAngle, both in degress, 0 to 359. I've got a function named rotateDirection(float sourceAngle, ...
69 views

### How to “aim ahead of” an object moving in a circle? [duplicate]

Let's say I have a GameObject A that's moving in a circular path in orbit around a central point, and I have a second GameObject ...
108 views

### How to find perpendicular line given a line?

I have two points that form 1 line. I want to find a point that creates a perpendicular line. Here is an image showing what I am looking for: How do I find the red point to form a perpendicular ...
89 views

### Unity 3D rotating object around 2 axes rotates it around 3

I am developing a 3D space shooter and I've fount that when triying to rotate the ship using X and Y axes it also rotates on the Z axe. The answer here helped me a lot, but now when I try to rotate ...
33 views

### Get the mesh Project Plane on Click and calculate its area

Here is the excerpt of my script which is calculating the surface area and face area of a mesh on OnMouseDown Event. ...
106 views

### Get triangles after subdivision

I was able to do subdivision on a triangle mesh with midpoints but then I get polygons with too many faces. How do I convert to triangles after? Similar to this picture:
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### Calculating approximations of contact between two meshes

I'm looking for ways to calculate the degree of contact between two objects in a scene. I was thinking that calculating the hausdorff distance would be a useful approximation if it is then normalized ...
19 views

### Can I slightly rotate a 2D vector (UV Edge) to more closely reflect the corresponding 3d vector?

I'm trying to get the difference between the 3D angle of two connected edges and their corresponding angle in 2D (mesh to UV space). I would like to slightly rotate the angle in 2D to closer match ...
421 views

### How does a 4x4 matrix represent an object in space and matrix lore?

I have been following some tutorials on how Matrix maths works, with adding, dividing, scaling, etc, but I am struggling to understand how the 4x4 matrix represents an object's position in space. ...
1k views

### Formula to measure uv-mapping distortion

Does anyone know a simple way of calculating (offline) the amount a texture is distorted when mapped to a triangle like the following? ...
169 views

### How do I launch a ballistic projectile to hit a moving target, given: launch position & angle, target position & velocity?

This problem is in 3D space. My question is: How do you find the initial velocity of a projectile that flies under constant gravity, so that it hits a target moving with constant velocity, given the ...
19 views

I am very new to Maya and trying to make a Nikon F camera from reference images. I can't quite wrap my head around how I would make the shape on top of the camera because it is essentially a square ...
12k views

### How do I find the circumcenter of a triangle in 3D?

I want to find the circumcenter of a triangle. Wolfram only shows how to find the circumcircle of a triangle in R2. How can I find the circumcenter of a triangle in R3?
36 views

### Generation of a 3D loop the loop with minimal steering required

How would I generate a surface which resembles a loop-the-loop shape like this one described here? After triangulation of the surface, lets say I start at one end with some initial velocity which is ...
53 views

### How to know if two surface are in the same direction?

In my code I creat a Mesh that are composed by multiple tile. those tile can have edge that are shared, and I need to know if the normal of the tile that have shared edge have the same direction, ...
15k views

### How to move an object along a vector

Let's say I got an object A and object B in a 2D game. I create a vector leading from A to <...
491 views

### Get closest point on box to line

Eventually this problem will be 3D, so I would like a solution that works in 3D. My player is looking forwards. There is an axis-aligned box on the screen (FOV is guaranteed to be 90, so boxes behind ...