Sign in to follow this  

OpenGL Matrix layout in OpenGL, DirectX and AGAL

Recommended Posts

Hello. I'm totally stuck in vector and matrix multiplication. I can't sleep 2 days - there're matrices in my head. AGAL - Adobe Graphics Assembly Language - is used in stage3D API in ActionScrips. And it's beast. I don't know OpenGL and DirectX, and it hard to say what AGAL is similar to. I know, for example that it uses right handed coordinate system - i.e. like in DirectX. But I can't say anything about matrices. Here's documentation about vector and matrix multiplication:

[quote]destination.x = (source1.x * source2[0].x) + (source1.y * source2[0].y) + (source1.z * source2[0].z)
destination.y = (source1.x * source2[1].x) + (source1.y * source2[1].y) + (source1.z * source2[1].z)
destination.z = (source1.x * source2[2].x) + (source1.y * source2[2].y) + (source1.z * source2[2].z)[/quote]

Here source1 is vector and source2 is matrix (actualy array of vectors). Documentation doesn't say what side from matrix the vector is - from left or right. I write down on paper this multiplication and this is what I get:

Here multiplication like in DirectX - row vector which means that matrix have row layout
[font=courier new,courier,monospace]........|x0 y0 z0|
|x y z| |x1 y1 z1| = |x * x0 + y * x1 + z * x2, x * y0 + y * y1 + z * y2, x * z0 + y * z1 + z * z2|
........|x2 y2 z2|[/font]
And it differs from documentation.

Ok, let's try OpenGL rule - column layout matrix and column vector
[font=courier new,courier,monospace]|x0 x1 x2| |x|
|y0 y1 y2| |y|[/font][font=courier new,courier,monospace] = |x * x0 + y * x1 + z * x2, x * y0 + y * y1 + z * y2, x * z0 + y * z1 + z * z2|[/font]
[font=courier new,courier,monospace]|z0 z1 z2| |z|[/font]
Same as before - not as in documentation.

But if I transpose matrix - all fine - documentation and paper calculations are the same. And my question is - is it legal to multiply row vector wit column-layout matrix and column vector with row-layout matrix? I've digged tons of literature but I can't remember I saw this anywhere.

P.S.: I tried to write as clear as I can, but if there're any questions please ask. I need to solve this problem. Edited by Volgogradetzzz

Share this post

Link to post
Share on other sites
Stage3D should sort this out for you, you just need to upload a valid matrix or vector.<Number> and it will ensure it works fine on DirectX and OpenGL.

If you use the matrix3d class that is inbuilt just make sure you always set the transpose flag when you upload it.

Consistency is the key here, if using transposed matrices, then always do, don't mix and match :)

Share this post

Link to post
Share on other sites
Whether the matrix is row or column major has nothing to do whether you can multiply it with a vector or not. The major-ness of a matrix is only a way to determine how a matrix is converted from a 2-dimensional entity to a 1-dimensional layout for storage in memory. It tells you where in the memory you find the different values of the matrix. The matrix itself is still the same matrix no matter what major-ness you use or where, or how, you store the actual values. What has to change in your code when you change major-ness is only how you access the elements of the matrix.

edit: And as bwhiting said before me: consistency is the key. Know what you're doing, and do it consistently. If you define a specific major-ness, then you need to ensure that you access your matrix according to that rule. Similarly, if you define for example column vectors, then you can only multiply them from the right, but major-ness is, from a mathematical point of view, totally irrelevant to the actual multiplication. Edited by Brother Bob

Share this post

Link to post
Share on other sites
Wow, so fast.
Ben, I don't want use matrix3D for several reasons so I'm trying to pass matrix through 4 calls of setVertexVectorConstant().
Bob, I read your previous great posts but I mean no major-ness of matrix but layout. For example rotation matrix in DirectX have it's rows as basis, In openGL basis are columns. Or take a translational part of 4x4 matrix. If we have vector on the left the translational vector in matrix should be exactly 4-th row - it cannot be 4-th column or we get wrong results. In my example I pass 4 vectors and they should form a matrix. But if you write this vector either as rows or columns and multiply by some vector you wil not get the answer like in documentation. And I'm very interesting why?

Share this post

Link to post
Share on other sites
I misuderstood your question then. But re-reading it again with the new context, I'm not sure what it is you're asking. Is it that it seems like the OpenGL and Direct3D matrices has to be transposed to match the operations performed by AGAL?

In that case, it could simply be that AGAL uses different vectors and matrix major-ness. That would mean that, for example, source2[0] in the code from your first post is in fact not the first basis vector, but a vector of the x-components of all basis vectors. That is a result of using a mixed vector and matrix major-ness.

This is not the same as having column vectors and a matrix with row-basis vector or vice versa. It's just that the matrix is ordered differently in memory compared to OpenGL or Direct3D. It is in no way wrong and as I said in my first post it is entirely about defining where the elements go in the memory. OpenGL and Direct3D both have the basis vectors of their matrices linearly in memory, but if my assumption here is correct then AGAL does not have its basis vectors linearly in memory as a result of different basis-ness and major-ness. Edited by Brother Bob

Share this post

Link to post
Share on other sites
Thanks, Brother Bob, it makes sence. But there're still many questions. source2[0] is basis vector for sure. And it seems that there're mistake in documentation (quote in 1st post). Anyway I made some tests and it looks like we have column-layout matrix and so column vectors. So we have DirectX-like coordinate system and OpenGL-like matrix operations. Best from both worlds.

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  

  • Forum Statistics

    • Total Topics
    • Total Posts
  • Similar Content

    • By DelicateTreeFrog
      Hello! As an exercise for delving into modern OpenGL, I'm creating a simple .obj renderer. I want to support things like varying degrees of specularity, geometry opacity, things like that, on a per-material basis. Different materials can also have different textures. Basic .obj necessities. I've done this in old school OpenGL, but modern OpenGL has its own thing going on, and I'd like to conform as closely to the standards as possible so as to keep the program running correctly, and I'm hoping to avoid picking up bad habits this early on.
      Reading around on the OpenGL Wiki, one tip in particular really stands out to me on this page:
      For something like a renderer for .obj files, this sort of thing seems almost ideal, but according to the wiki, it's a bad idea. Interesting to note!
      So, here's what the plan is so far as far as loading goes:
      Set up a type for materials so that materials can be created and destroyed. They will contain things like diffuse color, diffuse texture, geometry opacity, and so on, for each material in the .mtl file. Since .obj files are conveniently split up by material, I can load different groups of vertices/normals/UVs and triangles into different blocks of data for different models. When it comes to the rendering, I get a bit lost. I can either:
      Between drawing triangle groups, call glUseProgram to use a different shader for that particular geometry (so a unique shader just for the material that is shared by this triangle group). or
      Between drawing triangle groups, call glUniform a few times to adjust different parameters within the "master shader", such as specularity, diffuse color, and geometry opacity. In both cases, I still have to call glBindTexture between drawing triangle groups in order to bind the diffuse texture used by the material, so there doesn't seem to be a way around having the CPU do *something* during the rendering process instead of letting the GPU do everything all at once.
      The second option here seems less cluttered, however. There are less shaders to keep up with while one "master shader" handles it all. I don't have to duplicate any code or compile multiple shaders. Arguably, I could always have the shader program for each material be embedded in the material itself, and be auto-generated upon loading the material from the .mtl file. But this still leads to constantly calling glUseProgram, much more than is probably necessary in order to properly render the .obj. There seem to be a number of differing opinions on if it's okay to use hundreds of shaders or if it's best to just use tens of shaders.
      So, ultimately, what is the "right" way to do this? Does using a "master shader" (or a few variants of one) bog down the system compared to using hundreds of shader programs each dedicated to their own corresponding materials? Keeping in mind that the "master shaders" would have to track these additional uniforms and potentially have numerous branches of ifs, it may be possible that the ifs will lead to additional and unnecessary processing. But would that more expensive than constantly calling glUseProgram to switch shaders, or storing the shaders to begin with?
      With all these angles to consider, it's difficult to come to a conclusion. Both possible methods work, and both seem rather convenient for their own reasons, but which is the most performant? Please help this beginner/dummy understand. Thank you!
    • By JJCDeveloper
      I want to make professional java 3d game with server program and database,packet handling for multiplayer and client-server communicating,maps rendering,models,and stuffs Which aspect of java can I learn and where can I learn java Lwjgl OpenGL rendering Like minecraft and world of tanks
    • By AyeRonTarpas
      A friend of mine and I are making a 2D game engine as a learning experience and to hopefully build upon the experience in the long run.

      -What I'm using:
          C++;. Since im learning this language while in college and its one of the popular language to make games with why not.     Visual Studios; Im using a windows so yea.     SDL or GLFW; was thinking about SDL since i do some research on it where it is catching my interest but i hear SDL is a huge package compared to GLFW, so i may do GLFW to start with as learning since i may get overwhelmed with SDL.  
      Knowing what we want in the engine what should our main focus be in terms of learning. File managements, with headers, functions ect. How can i properly manage files with out confusing myself and my friend when sharing code. Alternative to Visual studios: My friend has a mac and cant properly use Vis studios, is there another alternative to it?  
    • By ferreiradaselva
      Both functions are available since 3.0, and I'm currently using `glMapBuffer()`, which works fine.
      But, I was wondering if anyone has experienced advantage in using `glMapBufferRange()`, which allows to specify the range of the mapped buffer. Could this be only a safety measure or does it improve performance?
      Note: I'm not asking about glBufferSubData()/glBufferData. Those two are irrelevant in this case.
    • By xhcao
      Before using void glBindImageTexture(    GLuint unit, GLuint texture, GLint level, GLboolean layered, GLint layer, GLenum access, GLenum format), does need to make sure that texture is completeness. 
  • Popular Now