Questions tagged [projection-matrix]

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13 votes
2 answers
4k views

Why do we need a fourth coordinate to divide by z?

I read the response here: What does the graphics card do with the fourth element of a vector as the final position? "The fourth component is a trick to keep track of perspective projection. When ...
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10 votes
5 answers
4k views

How do I correctly project a point behind the camera?

I am making a 3D game in which I put an exclamation marker above points of interest. In order to find out where in the 2D screen should I put my marker, I am manually projecting the 3D point where ...
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9 votes
1 answer
123 views

How to clip cut-off using different frustrum than that of original camera? How to cut plane by pyramid shape?

SOURCE : http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2012/10/Mitchell_LightShafts.pdf This process is part of creating light draft effect. And I am suggested to do the described process in ...
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8 votes
2 answers
334 views

How do I create a half-ortho half-perspective projection matrix

I've been trying to make a formula for the projection matrix where your vertical axis is projected orthographically but your horizontal axis will have perspective to it. So the view frustum would look ...
7 votes
1 answer
470 views

How to set the camera projection matrix so that its 4 rays always exactly hit the corners of a defined rectangle?

I have a camera, and I have a rectangle drawn in an arbitrary plane. I need to change the projection matrix of the camera so that the rays along the edges of the camera's frustum always hit the ...
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6 votes
1 answer
2k views

How does a game like Enter the Gungeon handle forward and backwards movement with their orthographic set up?

So I've been scratching my head at this problem for over a week now, and would love some insight from anyone who might know a bit more. In my game I have the floor flat on the X/Z plane with walls/...
  • 131
4 votes
2 answers
2k views

360 degree video of my OpenGL game

I want to make a 360 degree video of my OpenGL game. Concerning the rendering: Is it enough to render it in OpenGL with a specific projection matrix? If yes, which one? Or can I render it into a cube ...
  • 91
4 votes
1 answer
479 views

OpenGL: How to map point inside frustrum to normal device coordinates (NDC)?

I read this article http://www.songho.ca/opengl/gl_projectionmatrix.html. It's explain how calculate projection matrix coefficients. But I completely can't understand how author perform mapping from ...
3 votes
1 answer
1k views

Offset a camera/render without changing perspective

I need to offset a render so that the perspective / vanishing point doesn't change. Or another way to look at it is that I need to adjust the vanishing point in my view so that instead of being at 0,...
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3 votes
1 answer
115 views

OpenGL Perspective Issue

I'm trying to troubleshoot a problem with my simple OpenGL test program, which I've written in C. I've written some math routines to do the matrix manipulation, but even after copying known working ...
  • 51
3 votes
1 answer
4k views

libGDX - Why do I have to use camera.setToOrtho what does it do?

I am very confused about camera matrices and I don't know where to start my studying. Maybe I have to study OpenGL, but I don't know C++ ... Ok so I have a camera, Box2d world and a Box2d body. <...
3 votes
1 answer
4k views

Deproject Screen To World Coordinates (Unreal Engine 4.15)

I am working on a small game in Unreal Engine 4.15 using blueprints only and encountered a behaviour I don't understand. The game is based on the Top Down Example. As I'd like to teleport an actor ...
  • 31
3 votes
0 answers
575 views

Control frustum near and far clip plane sizes in a Projection Matrix

I'm trying to achieve a dolly zoom effect. My first try was the obvious one, the original "zoom in & dolly out" technique, which works nicely. Except that there are cases which this is not ...
  • 389
2 votes
2 answers
10k views

How can I set up an intuitive perspective projection/view matrix combination in OpenGL, using GLM?

Could anyone help me set up an intuitive perspective camera matrix using OpenGL and the GLM library? By "intuitive" I mean that I want the camera to be looking at the middle of the screen down the -Z ...
  • 187
2 votes
2 answers
1k views

OpenGL: Is it efficient ok to glPushMatrix, plMultMatrix, plPopMatrix for every object in my scene?

I'm very new to opengl, and I might not fully understand the openGL matrix projection stack thing. So, I have about 300 'objects' in my scene, each with their own position/rotation, and I want to ...
2 votes
3 answers
3k views

Why should i set glClearColor and setProjectionMatrix in render method many time in LibGDX?

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2 votes
1 answer
153 views

What are some standard mathematical tests for projection matrices?

I'm trying to double check my math in my projection matrices. I'm thinking about "unit tests" when I ask this. I'm looking for 4 or 5 unit tests that would be appropriate to give one confidence that ...
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2 votes
1 answer
140 views

Shaders wont bind to the uniform block

I'm having an issue with interface block binding. Example shader: ...
  • 31
2 votes
1 answer
751 views

Why does the projection matrix transform object points into a unit cube in computer graphics?

This semester I both took a computer vision and a computer graphics seminar. But only now before the exams I realize that there seems to be a fundamental difference between projection in both topics. ...
  • 123
2 votes
0 answers
1k views

How to achieve the top-down (oblique) projection of textures using an OrthographicCamera?

This question is related to (How to calculate the initial velocity of projectile motion by a given distance and angle from point A to B) question. Details In the below image is the graphical ...
  • 491
1 vote
1 answer
54 views

Can I get world-space z-near-plane vertices from projection matrix + z-near distance?

I'm trying to port ShaderToy VR shaders to WebXR (the new browser API for AR/VR devices). ShaderToy VR shaders expect two extra parameters: ray origin (view translation) and ray direction (unit vector ...
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1 vote
1 answer
543 views

OpenGL frustum extraction

I'm trying to extract frustum planes from the camera. The algorithm is simple: create clip to world space matrix (inversed projection * inversed view) multiply clip point by clip to world matrix ...
  • 108
1 vote
2 answers
2k views

libGDX - orthographic camera and world units

I've followed the advice in this post to handle world/screen coordinates, but I'm getting results I don't quite understand, as I'm not terribly good in math. So, when I use this code: ...
1 vote
1 answer
316 views

Last Row of the perspective projection matrix

Could you explain to me what is the purpose of -1 in the last row of the gl_projection matrix? And how it affects the perspective division step ?
  • 189
1 vote
2 answers
9k views

How can I pass a std::vector<Vector3f> to my shader?

I have a Vector3f type which has x, y, and z properties. ...
1 vote
1 answer
238 views

Combining cylindrical Billboarding and aligning with velocity (unity)

I'm trying to make a custom GPU particle solution on Unity to fullfill some needs on my project, using compute shaders and custom shader + Graphics.DrawProceduralNow() to draw them. While I managed ...
1 vote
1 answer
369 views

set zfar/znear in openGL using shaders (QT env)

I have a QT canvas and I'm using shaders to build my scence. I've set the camera image plane at some position, and would like to view object from the image plane to infinity. How do I set the zfar and ...
  • 111
1 vote
1 answer
92 views

2D World Mouse Coordinates - Matrices

I'm trying to get the world coordinates out of a mouse click. Currently I'm doing the following: ...
1 vote
1 answer
100 views

What are projection independent ways of determining whether a normal is facing the viewer?

A position v and normal n are given in world coordinates. Also there is a view matrix V for ...
1 vote
1 answer
194 views

HLSL pixel inside a view (cascaded shadowmapping)

I'm figuring out shadowmapping in HLSL (see also this question). I understand that I need projection matrices for each cascading shadowmap. I use this code to create the projections: ...
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1 vote
0 answers
116 views

How to get world coordinates from a 4X4 camera matrix

I have Intel T265 camera which has a camera coordinates system like following diagram: The camera system has two cameras and the center of the two cameras is the position of the camera system. The ...
1 vote
0 answers
47 views

My triangle disappears when multiplaying by my perspective projection matrix

Whenever I multiply my transformation matrix, which is passed to the shader via constant buffer, my triangle disappears. Here is the code for the passed matrix: ...
1 vote
0 answers
69 views

Why projection window is between -1 and 1

Is it a convetion ? What we achieve with this ? I am reading about how the perspective and orthographic matrix is getting calculated and everyone is trying to normalize the homogenous coordinates to [...
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1 vote
0 answers
81 views

How and where to transform a Camera Frustum onto a tilted screen?

In rendering tutorials for perspective projection the assumption is that the rendering surface is perpendicular to the sight line. As shown here: How to accommodate for a screen that is tilted ...
  • 185
1 vote
1 answer
3k views

From screen space to world space for a 2D game

I'm making a 2D game and I want the user to be able to position an object in the world using mouse input. After a while I found an answer to 'OpenGL Math - Projecting Screen space to World space ...
  • 113
1 vote
0 answers
54 views

Convert box to matrix

I have a box (non-rectangular cuboid?) and would like to convert it to a matrix such that when a point inside the box is multiplied by the matrix, a vector is returned that describes the relative ...
1 vote
1 answer
779 views

Converting normalized device coordinates to world space coordinates flipping my sprites

I'm trying to convert my game's camera system to use world space coordinates rather than OpenGL's default normalized device coordinates, however in doing so my sprites are being rendered improperly as ...
1 vote
0 answers
1k views

How can I get shadows to appear correctly when using a custom projection matrix?

EDIT: This has been officially marked as a bug in Unity. If anyone else has this issue, you can vote here for Unity to fix it. As mentioned in this thread, I'm using a custom projection matrix in ...
1 vote
1 answer
357 views

How to position a Weapons model in a first person shooter with XNA

I am building a first person shooter and positioning the weapons is hard. I am trying to get the bat to look like you are holding it but I keep trying things and they don't appear in the positions I ...
0 votes
1 answer
92 views

Does a Standard Exist for Game Entity View Frustums

I was just recently adding the ability for my in-game entities to have their own Frustums, with the intentions of making them able to see enemies later down the road of my development cycle. My custom ...
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0 votes
1 answer
172 views

Projection Matrix Breaks My Rectangle

This is my vertex shader, shown below. ...
  • 1,116
0 votes
3 answers
80 views

When moving the "camera" should one move the projection matrix or move the world?

I'm making my own game engine as an exercise and I've gotten really confused with what I've read so far. When I want to move my camera do I simply just move the world or move the position of the ...
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0 votes
1 answer
128 views

How to visualize angle of projection in Oblique Parallel Projection?

We know that in Oblique Parallel Projection Point (x,y,z) is projected to position (x_p,y_p) on the view plane.Projector (oblique) from (x,y,z) to (x_p,y_p) makes an angle alpha. with the line (L) on ...
0 votes
1 answer
74 views

Texture flipping behaviour

I was having this problem with OpenGL where I'd have all my textures being rendered upside down. I did the most logical thing I could think of and tried reversing the order of the mapping and that ...
0 votes
1 answer
833 views

What exactly does XMMatrixPerspective{L,R}H do?

There are generally three functions to create a perspective matrix in DirectXMath, XMMatrixPerspective{L,R}H, ...
  • 1,840
0 votes
2 answers
1k views

Z-Value of clip-space position is always 1.0

I render a lot of quads on the screen into z direction (20 x 2000). I want to get the depth value in a final render target. But it looks like z is always 1.0f. I checked the result with the OpenGL ...
  • 111
0 votes
1 answer
2k views

How does glm::lookAt produce a View Matrix?

Say we do this: glm::mat4 View = glm::lookAt(glm::vec3(4,3,-3), glm::vec3(0,0,0),glm::vec3(0,1,0)); And after printing to the console with glm tostring (column ...
  • 11
0 votes
1 answer
67 views

Confused about why my projection matrix works

My projection matrix was buggy, I'm not great at mathematics, but I checked it against the the songho tutorial, and the broken one seems correct to me but switching nearplane to farplane seems to ...
0 votes
1 answer
687 views

How to set ortho projection / model view matrix without a camera?

I'm trying to create the correct projection and model view matrix for rendering without a camera. _orthoCamera is a camera I set up in the scene view. Using the <...
  • 11
0 votes
1 answer
307 views

OpenGL orthographic projection rendering quarter of screen

I'm trying to set up an orthographic projection so I can draw a rectangle using screen coordinates, but even if I draw a rectangle using the width/height of the window, it only fills a quarter of the ...