Sign in to follow this  

OpenGL Picking and graphic chip troubles

Recommended Posts

floatingwoods    364
Hello, I have an opengl application that uses picking and reading the selection buffer to pick the object closest to the camera. That works well on all tested graphic cards, but not on my own computer at home which uses an intel G33/G31 Express chipset family. In that case, the depth value is always 0 in the selection buffer and the application can't figure out which object is closest to the camera. Now my question is: is that really a problem of my graphic chip? When I turn all graphic accelerations off, the application picks fine, but rendering time is 10 time slowlier!! Is there some workaround? Or how do professional applications guaranty picking working on all graphic chips? Thanks!

Share this post

Link to post
Share on other sites
swiftcoder    18432
Fairly few applications use the OpenGL selection mode, for a couple of reasons: it is limited to only 64 objects in many implementations, and driver support can be very spotty.

The next simplest method is to use the gluUnproject function in concert with the depth buffer, which can give you the exact point of the mouse-click in 3-dimensional space, and you can then compare this point with your objects to pick the right one.

Share this post

Link to post
Share on other sites
floatingwoods    364
Thanks for the replies!
I actually could find some other people who are having the same kind of troubles with the same graphic chip, so it must be a hardware (or driver) problem.

Swiftcoder: what you are describing is not picking. I actually also extract the 3D position of my cursor by reading the depth buffer (but for some different reasons). Of course I could compare that 3D position with the center position (or vertice position) of each of my objects, but this does not work when objects are close to each other (or you'll end picking the wrong objects). What I mean to say is your solution is not pixel-accurate.

V-Man: I am surprised by what I read there. That means I should implement the picking by doing a rendering pass with specific colors for each object. That works fine for picking, but I also have a "rectangle selection"-mode, where everything inside a rectangle that I draw on the screen gets selected. Using color-coded picking would not pick my hidden objects (hidden, but still inside the rectangle).

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++.
      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