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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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Is it possible to generate a 2D surface that approaches certain mesh, and then a specialised ray-tracing function for it?

As an example, suppose we are trying to ray-trace a sphere. There are two options. The first one is to build a mesh of triangles approximating the sphere and ray trace it. Unfortunately, the more ...
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3answers
323 views

exact point on a rotating sphere

I have a sphere that represents the Earth textured with real pictures. It's rotating around the x axis, and when user click down it has to show me the exact place he clicked on. For example if he ...
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1answer
20 views

Interpreting focal length in units of pixels

I am working on a renderer of sorts and I have some fundamental questions. Let's say I have a vector in a 3D virtual world space which is unitless, and I want to project it onto a 2D screen, so I need ...
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0answers
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Rotate projectile toward target [on hold]

Rotating a projectile toward a target Say I had a bullet a character shoots at an enemy. If the enemy was directly above me I want the bullet to be rotated at a 90 degree angle. Or if the bullet ...
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2answers
988 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 ...
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2answers
216 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 ...
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1answer
13 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. ...
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1answer
65 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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2answers
904 views

How can I mask this CanvasRenderer?

I'm creating a text box that allows for selectable text, based off of Unity's InputField. An issue I am now facing is that the selection highlight does not respond to masks (The parent has a mask, but ...
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1answer
13 views

Get closest point on box to line

Eventually this problem will be 3D. My player is looking forwards. There is an axis-aligned box on the screen (FOV is guaranteed to be 90, so boxes behind the player aren't considered.) I want to ...
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1answer
344 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:...
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1answer
247 views

Rotate perspective camera to align screen width to procedural object's width (Unity, C#)

I give up. After much trying and searching, I have to say I was unable to achieve the following task, for which I must call for your wise advice. In my current Unity 5 application (using C#), there ...
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3answers
99 views

How can you tell if you are a large player on a large map or a small player on a small map?

If everything is scaled by a constant factor, can you tell that the world is smaller or larger? I think you could look down at the ground and see that it's "closer". But how do you know what ...
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1answer
44 views

How to implement level-player collisions resolution?

I want to create simple collision response system (physical simulation is not required now). It is needed just that player can't go through walls. I consider some variants: - Just create a set of ...
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1answer
162 views

How to calculate the surface area of a mesh

I am looking for a way to calculate surface area of a 3D mesh object and found this code from a Unity forum: ...
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1answer
63 views

How can I express Logarithmic and Arithmetic spirals as segmented cubic bezier curves?

I am creating cubic bezier curves using this code from another question I asked. I would like to know how I can express Logarithmic and Arithmetic spirals as segmented cubic bezier curves.
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1answer
63 views

How to inflate geometry?

I have a shape containing vertices and triangles I want to inflate that geometry using some radius to get something like that I should move each point along ...
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0answers
33 views

Geometrically aligning two 3D objects together?

Let's say I have 2 similar objects I need to align together about the target's center at runtime. Given their positions (x, y, z) and rotations in the world, how would I do this? They need to match ...
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1answer
8k views

How do you turn a cube into a sphere?

I'm trying to make a quad sphere based on an article, which shows results like this: I can generate a cube correctly: But when I convert all the points according to this formula (from the page ...
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1answer
310 views

Why are spherical worlds so rare?

I remember back in the 90s when X-Com came out, being really impressed by the way its world map was an actual world: a map of Earth drawn on a spherical surface. That was pretty cool, because I had ...
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1answer
76 views

Confused by scaling, units, and more

Ok, so I've already waded through a bunch of questions around this, and it's just making me even more confused. Let's say I am trying to model a card table in a 2d game. Behind (beneath) the table ...
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0answers
54 views

Weird behaviour of glsl with fragment, vertex and geometry shaders

I am a beginner in developing games. I started some time ago with OpenGL and the glsl language. These days I am having so many problems and for me it is too difficult to solve, because the shaders are ...
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1answer
63 views

Define a circle from a point on its circumference and an angle

I'm working on a 2D, top-down driving game with some basic AI vehicles. The AI Vehicles move along a bidirected graph of positions. Each vehicle has a current position (from the graph) and a target ...
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1answer
25 views

Determine view-matrix with camera placed in a scene graph

My scene is organized with a simple scene graph where the child multiplies its transformation with the one of the parent. For normal objects, likes meshes, this works as expected, but I also want to ...
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1answer
258 views

How to find a point on a plane?

I'm using unreal engine 4. Currently I ray trace to a surface in game and I'm trying to find the location of the point relative to the surface1 instead of the world. I have the world position of the ...
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2answers
3k views

What is a good way to determine if a vector is between two other vectors in 2D?

I could operate with the angles, but I do not have the angles calculated yet (and would like to avoid having to do that). It would be possible to calculate and cache the local-coordinate-frame angles, ...
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4answers
4k views

How do I efficiently check if a point is inside a rotated rectangle?

Part for the sake of optimization, part for learning purposes, I will dare to ask: How can I most efficiently check whether a 2D point P is inside a 2D rotated ...
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1answer
1k views

How do I calculate the distance between a point and a rotated rectangle?

This question is similar to another one about axis-aligned rectangles. However, I specifically want to calculate this for rotated rectangles. I have a rectangle with a (cx, cy) for the center point ...
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3answers
301 views

What's the most efficient way to find the position of a point in relation to corners of a rectangle despite rectangle's scale

I am struggling to achieve the following with C# (in Unity). I need to find the position of the points that lay at a given distance (let's say 1m) from the corners of a rectangle, in a way that the ...
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4answers
424 views

How do I interpolate around a rectangle?

I want to make a fancy animation where a point travels around a rectangle. I want to find the point's position at a time t. The rectangle is given by ...
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3answers
322 views

How to find the total bounds rectangle around a list of rectangles

How can I find the total bounds rectangle around a list of rectangles? Rectangle object: a simple data structure of 4 floats (w,h,x,y). I have an array of 2 or more rectangles and want to create a ...
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3answers
415 views

Divide rectangular image into fixed number of random sized rectangles + 1 fixed size rectangle

I'm trying to divide a rectangular image into a fixed number of smaller rectangular image parts (of random but bounded width / height), with the exception of 1 rectangle which is predefined in ...
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1answer
2k views

Get screen bounds of 3D object

I'm trying to draw a 2D plane that has minimum dimensions to contain a 3D model (a sphere). How do I calculate the minimum size and position of the rectangle to completely cover a 3D model on screen?
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0answers
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Tetrahedron Circumsphere

Following this question, I want to create a sphere from a tetrahedron using this Wolfram support. But so far the resulted sphere is bigger than it should be and center seems to have an offset. ...
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6answers
15k views

How do I calculate distance between a point and an axis-aligned rectangle?

I have a 2D rectangle with x, y position, height and width, and a randomly positioned point nearby. Is there a way to check if this point might collide with the rectangle if it is closer than a ...
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4answers
3k views

Find the closest point along a rectangle, given an another point and direction

Given a rectangle, and a point with a vector direction towards the rectangle. How can I find the closest point on the outside of that rectangle to the point in question?
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2answers
5k views

Triangle-Plane intersection in 3D space

I would like to clip a triangle if its bounds lie partially out of a cube. I guess I would need some kind of Triangle Plane intersection code - I'm not well versed with math but I do have the points ...
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2answers
1k views

Calculate the slope of a 3D triangle?

I have lots of triangles in 3D space. How do I determine the slope/angle of these triangles with respect to a fixed ground plane? I need pseudo code examples at the very least.
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1answer
135 views

Removing duplicate vertices on a mesh

I have a set of vertices and another set of indices. Sometimes I find that I have duplicate vertices in my mesh. I tried at first to check if two identical vertices were in the array of vertices but ...
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2answers
236 views

How to draw a 3D capsule?

I want to draw a 3D capsule defined by a segment (two points start->end) and a radius: Image source: Orionist on Wikimedia Commons I already have a sphere leaning on this answer: https://...
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1answer
9k 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?
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1answer
454 views

Does triangle-plane clipping in 3D always produce a triangle?

When you clip a triangle against a plane, will you always get a triangle out? Are there perhaps cases where you don't get a triangle out of clipping it against a plane?
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2answers
221 views

How can I convert my list of vertices and indices to a list of triangles?

I have a full 3D collision mesh that is represented by a list of vertices and another list of indices. I need to convert the list of vertices and the list of indices into a set of triangles. First I ...
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3answers
926 views

Adding tolerance to a point in polygon test

I've been using this method which was taken from Game Coding Complete to detect whether a point is inside of a polygon. It works in almost every case, but is failing on a few edge cases, and I can't ...
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2answers
7k views

How do I determine if one polygon completely contains another?

I have 2 polygons. I know the vertex coordinates of both polygons. What's the best way to check if one is completely inside the other? For example, the algorithm should only recognize the black ...
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1answer
944 views

Puzzle game: clipping of non-convex polygons on the figures

I have an original figure in the SVG file. I need to break it randomly on parts, an example of which is specified below: I have an idea, to use for partitioning Voronoi diagram (Fortune's algorithm). ...
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1answer
1k views

Algorithm for constructing the corners of a regular, n-sided polygon

I've googled this using a lot of keyword combinations, but to my great surprise I could not find an algorithm for constructing a regular, n-sided polygon into a given circle, i.e., finding the ...
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2answers
1k views

ray polygon intersection

I am looking for an elegant way to do ray and polygon intersections in 2d. I don't care about languages. Now what I'm doing is taking a line that lies on the ray (with a screen length) and testing ...
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5answers
2k views

How can I tell whether an object is moving CW or CCW around a connected path?

Lets say we have a jagged shape: And two creatures moving along it's outline. Then we smooth the shape completely by pulling the corners out. We get this: It is easy to see now that Orange is ...
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2answers
247 views

Splitting Graph into distinct polygons in O(E) complexity

If you have seen my last question: trapped inside a Graph : Find paths along edges that do not cross any edges How do you split an entire graph into distinct shapes 'trapped' inside the graph(like ...