Sign in to follow this  
kreaThor

OpenGL projection matrix with more than one vanishing point

Recommended Posts

kreaThor    122
Hello! I saw some very interesting pictures of a cube drawn by projecting it with a perspective projection with more than one vanishing point. Can this be done in OpenGL? If yes, how can the projection matrix be calculated?

Share this post


Link to post
Share on other sites
haegarr    7372
It is not fully clear: The "standard" perspective projection has 1, 2, or 3 vanishing points visible, dependend on how the viewed object is oriented and positioned w.r.t. the cam (to be precise: the projection plane).

However, dozens of kinds of (also perspective) projections exist. Unfortunately due to the fact that it could not be modeled using homogeneous matrix math most of them could not be simulated by OpenGL. Obviously no projections w/ curved projectors could be done. Also no "inverse" projection could be done (as far as I know). EDIT: Projections w/ curved projection planes could be done but only approximately.

Whether the projections you have in mind could be done isn't answerable as long as you don't name them. But I'm not confident.

Share this post


Link to post
Share on other sites
Sneftel    1788
Just do a Google image search for "two-point perspective" and you'll turn up plenty of examples.

Share this post


Link to post
Share on other sites
haegarr    7372
Quote:
Original post by kreaThor
ok U guys thanks. I will delve some more into the topic, though I understood from haegarr that it can't be done in opengl.

Notice please that I said that I'm not _confident_ that it will be possible, but due to lack of knowledge of what you've actually found I could not definitely say "yes" or "no".

The standard 1/2/3 point perspective projections work simply by unaligning the projection plane, as the site following Sneftel's link above shows. As a real projection mode, the unalignment is done by the projection matrix. However, the _effect_ is the same as could be seen if the objects are unaligned. E.g. take a wire-cube, and place the camera in front of it. What could be seen is a single vanishing point. Changing the heading of the cube by 45 degrees, and you see 2 vanishing points.

I somewhere have seen projections with more than 3 vanishing points. As far as I remember, these projections cannot be simulated by OpenGL.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Similar Content

    • By povilaslt2
      Hello. I'm Programmer who is in search of 2D game project who preferably uses OpenGL and C++. You can see my projects in GitHub. Project genre doesn't matter (except MMO's :D).
    • By ZeldaFan555
      Hello, My name is Matt. I am a programmer. I mostly use Java, but can use C++ and various other languages. I'm looking for someone to partner up with for random projects, preferably using OpenGL, though I'd be open to just about anything. If you're interested you can contact me on Skype or on here, thank you!
      Skype: Mangodoor408
    • By tyhender
      Hello, my name is Mark. I'm hobby programmer. 
      So recently,I thought that it's good idea to find people to create a full 3D engine. I'm looking for people experienced in scripting 3D shaders and implementing physics into engine(game)(we are going to use the React physics engine). 
      And,ye,no money =D I'm just looking for hobbyists that will be proud of their work. If engine(or game) will have financial succes,well,then maybe =D
      Sorry for late replies.
      I mostly give more information when people PM me,but this post is REALLY short,even for me =D
      So here's few more points:
      Engine will use openGL and SDL for graphics. It will use React3D physics library for physics simulation. Engine(most probably,atleast for the first part) won't have graphical fron-end,it will be a framework . I think final engine should be enough to set up an FPS in a couple of minutes. A bit about my self:
      I've been programming for 7 years total. I learned very slowly it as "secondary interesting thing" for like 3 years, but then began to script more seriously.  My primary language is C++,which we are going to use for the engine. Yes,I did 3D graphics with physics simulation before. No, my portfolio isn't very impressive. I'm working on that No,I wasn't employed officially. If anybody need to know more PM me. 
       
    • By Zaphyk
      I am developing my engine using the OpenGL 3.3 compatibility profile. It runs as expected on my NVIDIA card and on my Intel Card however when I tried it on an AMD setup it ran 3 times worse than on the other setups. Could this be a AMD driver thing or is this probably a problem with my OGL code? Could a different code standard create such bad performance?
    • By Kjell Andersson
      I'm trying to get some legacy OpenGL code to run with a shader pipeline,
      The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
      I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
      I've got a version 330 vertex shader to somewhat work:
      #version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
      What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
      Question:
      What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?
       
      Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.
  • Popular Now