Sign in to follow this  
staticVoid2

OpenGL Reflection Mapping and OpenGL's ModelView matrix problem

Recommended Posts

I'm having a slight problem with getting reflection/environment mapping working, everything seems to work ok until I start moving the camera around the reflection does not follow with it, this is because I am using an 'eye-space' reflection vector to index a 'world-space' cube-map. here is the glsl code: vertex shader:
	varying vec3 reflectVec;
	void main()
	{
		vec3 normal = normalize(gl_NormalMatrix * gl_Normal);
		gl_Position = ftransform();
		reflectVec = reflect(vec3(gl_ModelViewMatrix * gl_Vertex), normal);
	}

fragment shader:
	uniform samplerCube tex;
	varying vec3 reflectVec;
	void main()
	{
		gl_FragColor = textureCube( tex, normalize(reflectVec) );
	}

Is there anyway to convert the reflection vector back into world space without it going through the Model matrix but just rather by the inverse of the View matrix so that it can access the cube map?

Share this post


Link to post
Share on other sites
Do you have the eye position of your camera? If yes, then I would have a uniform that stores that position and then do the following in my vertex shader:

gl_Position = ftransform();
reflectVec = reflect(gl_Vertex.xyz - eyePosition, gl_Normal);


Note that here I'm assuming the model itself has no "local" transformations, and that the verticies/normals going into the vertex shader are already in world space. If there are transformations local to take the model into world space, you'll need to have uniforms for those.

I think this approach will be simpler, but if you really want to play around in view space, getting back to world space would require you to use the inverse (possibly transpose) of the top-left 3x3 submatrix of the "world -> view" matrix. Again, if there are no transformations taking the model into world space, this will simply be the inverse of gl_NormalMatrix. If you need a little more clarification, just let me know!

Disclaimer: I've never implemented this before ;P

[Edited by - aryx on March 9, 2010 11:18:31 AM]

Share this post


Link to post
Share on other sites
Quote:

Note that here I'm assuming the model itself has no "local" transformations


thats exactly the problem, because opengl treats the view and model matrix as one I can't simply transform the vertices and normals into world space without also transforming them into view space.

I think the fastest method would be to store a separate world matrix as a uniform in the shader but how would I be able to get the world matrix while still making calls to glRotatef and glTranslatef, would I be better to wrap these into other functions e.g.




_glRotatef(float angle, float x, float y, float z)
{
glPushMatrix();
glLoadMatrix(&g_WorldMatrix);
glRotatef(angle, x, y, z);
glGetFloatfv(GL_MODELVIEW_MATRIX, &g_WorldMatrix);
glPopMatrix();

glRotatef(angle, x, y, z);
}






or is there a simpler way I am overlooking?

[Edited by - staticVoid2 on March 9, 2010 1:02:26 PM]

Share this post


Link to post
Share on other sites
My apologies for not replying sooner, but an old friend dropped by for a visit. One possible approach is the way you've shown. The only thing I would do differently is to fetch the matrix after it's fully constructed instead of every time I make a rotate/translate/scale call.

Another approach would be to have your own matrix manipulation code. The fixed-function stuff is all labeled as deprecated in the OpenGL 3 specs (but they'll still function for quite some time). If you're not doing anything too complicated then you'll probably only need some rotate/scale/translate functionality along with matrix multiplication. With this approach you'll be more prepared to switch to OpenGL 3 (e.g., glLoadMatrix will simply be replaced by a call to set some matrix uniforms in your shaders). This way you can separate the model transformations and view transformations yourself by keeping track of them separately.

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  

  • Announcements

  • Forum Statistics

    • Total Topics
      628390
    • Total Posts
      2982412
  • Similar Content

    • By test opty
      Hi all,
       
      I'm starting OpenGL using a tut on the Web. But at this point I would like to know the primitives needed for creating a window using OpenGL. So on Windows and using MS VS 2017, what is the simplest code required to render a window with the title of "First Rectangle", please?
       
       
    • By DejayHextrix
      Hi, New here. 
      I need some help. My fiance and I like to play this mobile game online that goes by real time. Her and I are always working but when we have free time we like to play this game. We don't always got time throughout the day to Queue Buildings, troops, Upgrades....etc.... 
      I was told to look into DLL Injection and OpenGL/DirectX Hooking. Is this true? Is this what I need to learn? 
      How do I read the Android files, or modify the files, or get the in-game tags/variables for the game I want? 
      Any assistance on this would be most appreciated. I been everywhere and seems no one knows or is to lazy to help me out. It would be nice to have assistance for once. I don't know what I need to learn. 
      So links of topics I need to learn within the comment section would be SOOOOO.....Helpful. Anything to just get me started. 
      Thanks, 
      Dejay Hextrix 
    • By mellinoe
      Hi all,
      First time poster here, although I've been reading posts here for quite a while. This place has been invaluable for learning graphics programming -- thanks for a great resource!
      Right now, I'm working on a graphics abstraction layer for .NET which supports D3D11, Vulkan, and OpenGL at the moment. I have implemented most of my planned features already, and things are working well. Some remaining features that I am planning are Compute Shaders, and some flavor of read-write shader resources. At the moment, my shaders can just get simple read-only access to a uniform (or constant) buffer, a texture, or a sampler. Unfortunately, I'm having a tough time grasping the distinctions between all of the different kinds of read-write resources that are available. In D3D alone, there seem to be 5 or 6 different kinds of resources with similar but different characteristics. On top of that, I get the impression that some of them are more or less "obsoleted" by the newer kinds, and don't have much of a place in modern code. There seem to be a few pivots:
      The data source/destination (buffer or texture) Read-write or read-only Structured or unstructured (?) Ordered vs unordered (?) These are just my observations based on a lot of MSDN and OpenGL doc reading. For my library, I'm not interested in exposing every possibility to the user -- just trying to find a good "middle-ground" that can be represented cleanly across API's which is good enough for common scenarios.
      Can anyone give a sort of "overview" of the different options, and perhaps compare/contrast the concepts between Direct3D, OpenGL, and Vulkan? I'd also be very interested in hearing how other folks have abstracted these concepts in their libraries.
    • By aejt
      I recently started getting into graphics programming (2nd try, first try was many years ago) and I'm working on a 3d rendering engine which I hope to be able to make a 3D game with sooner or later. I have plenty of C++ experience, but not a lot when it comes to graphics, and while it's definitely going much better this time, I'm having trouble figuring out how assets are usually handled by engines.
      I'm not having trouble with handling the GPU resources, but more so with how the resources should be defined and used in the system (materials, models, etc).
      This is my plan now, I've implemented most of it except for the XML parts and factories and those are the ones I'm not sure of at all:
      I have these classes:
      For GPU resources:
      Geometry: holds and manages everything needed to render a geometry: VAO, VBO, EBO. Texture: holds and manages a texture which is loaded into the GPU. Shader: holds and manages a shader which is loaded into the GPU. For assets relying on GPU resources:
      Material: holds a shader resource, multiple texture resources, as well as uniform settings. Mesh: holds a geometry and a material. Model: holds multiple meshes, possibly in a tree structure to more easily support skinning later on? For handling GPU resources:
      ResourceCache<T>: T can be any resource loaded into the GPU. It owns these resources and only hands out handles to them on request (currently string identifiers are used when requesting handles, but all resources are stored in a vector and each handle only contains resource's index in that vector) Resource<T>: The handles given out from ResourceCache. The handles are reference counted and to get the underlying resource you simply deference like with pointers (*handle).  
      And my plan is to define everything into these XML documents to abstract away files:
      Resources.xml for ref-counted GPU resources (geometry, shaders, textures) Resources are assigned names/ids and resource files, and possibly some attributes (what vertex attributes does this geometry have? what vertex attributes does this shader expect? what uniforms does this shader use? and so on) Are reference counted using ResourceCache<T> Assets.xml for assets using the GPU resources (materials, meshes, models) Assets are not reference counted, but they hold handles to ref-counted resources. References the resources defined in Resources.xml by names/ids. The XMLs are loaded into some structure in memory which is then used for loading the resources/assets using factory classes:
      Factory classes for resources:
      For example, a texture factory could contain the texture definitions from the XML containing data about textures in the game, as well as a cache containing all loaded textures. This means it has mappings from each name/id to a file and when asked to load a texture with a name/id, it can look up its path and use a "BinaryLoader" to either load the file and create the resource directly, or asynchronously load the file's data into a queue which then can be read from later to create the resources synchronously in the GL context. These factories only return handles.
      Factory classes for assets:
      Much like for resources, these classes contain the definitions for the assets they can load. For example, with the definition the MaterialFactory will know which shader, textures and possibly uniform a certain material has, and with the help of TextureFactory and ShaderFactory, it can retrieve handles to the resources it needs (Shader + Textures), setup itself from XML data (uniform values), and return a created instance of requested material. These factories return actual instances, not handles (but the instances contain handles).
       
       
      Is this a good or commonly used approach? Is this going to bite me in the ass later on? Are there other more preferable approaches? Is this outside of the scope of a 3d renderer and should be on the engine side? I'd love to receive and kind of advice or suggestions!
      Thanks!
    • By nedondev
      I 'm learning how to create game by using opengl with c/c++ coding, so here is my fist game. In video description also have game contain in Dropbox. May be I will make it better in future.
      Thanks.
  • Popular Now