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Porting to OpenGL


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#1 solenoidz   Members   -  Reputation: 531

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Posted 27 December 2012 - 05:35 AM

Hello people.

 

I have a Direct3D 9.0 engine and I want to add an OpenGL renderer.

The engine uses deferred lighting with Shader model 3.0 and unfortunately isn't written in abstraction level in mind. I mean, it uses DirectX types, objects and D3DX calls all over the code. 

My questions are :

1. What OpenGL version I should implement ? OpenGL 2.x , 3.x, 4.0 ? I need a smooth transition and easy port, that matches Direct3D 9.0 functionality well.

 2. Should I use glew, glut, SDL , other stuff like that ? I will most probably want to port it to other platforms like Linux, Mac ? I don't want to mess with extensions so probably glew will be of help.

3. Should I use nVidia CG shader language in order to use my existing HLSL shader code directly, without rewriting them to GLSL ?

4. Is there a good sample source code, tutorials, articles that show basic deferred rendering with a modern  OpenGL way  ( version 3 ++) ?

5. I'm using D3DX library for common math stuff etc, is there a library for OpenGL that is to it, like D3DX is to Direct3D ?

 

I have a limited OpenGL experience from the past.

 

Thank you.

More questions to come.



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#2 Yours3!f   Members   -  Reputation: 1340

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Posted 27 December 2012 - 06:16 AM

Hello people.

 

I have a Direct3D 9.0 engine and I want to add an OpenGL renderer.

The engine uses deferred lighting with Shader model 3.0 and unfortunately isn't written in abstraction level in mind. I mean, it uses DirectX types, objects and D3DX calls all over the code. 

My questions are :

1. What OpenGL version I should implement ? OpenGL 2.x , 3.x, 4.0 ? I need a smooth transition and easy port, that matches Direct3D 9.0 functionality well.

 2. Should I use glew, glut, SDL , other stuff like that ? I will most probably want to port it to other platforms like Linux, Mac ? I don't want to mess with extensions so probably glew will be of help.

3. Should I use nVidia CG shader language in order to use my existing HLSL shader code directly, without rewriting them to GLSL ?

4. Is there a good sample source code, tutorials, articles that show basic deferred rendering with a modern  OpenGL way  ( version 3 ++) ?

5. I'm using D3DX library for common math stuff etc, is there a library for OpenGL that is to it, like D3DX is to Direct3D ?

 

I have a limited OpenGL experience from the past.

 

Thank you.

More questions to come.

 

hi,

 

opengl 2.1 matches dx9 functionality.

yes you should use glew and sdl (or sfml, if you prefer c++-ish solutions), but these are not mandatory, you can write your own.

well cg is another language right? so you would have to port to cg then... the question is, do you want to learn glsl or not?

see: http://ogldev.atspace.co.uk/

but there are tons of others. google is your friend.

well for mesh loading and stuff related to that, you have assimp

for texture loading, you can do this with sdl / sfml. Just load in an image using sdl / sfml, acquire the pointer to the raw data, and fill a texture using that data.

for maths, you have tons of choices. The most popular ones are CML (http://cmldev.net) and GLM (http://glm.g-truc.net/).

I have also developed a math library: https://github.com/Yours3lf/libmymath

 

if you need anythin else, just go to the topics (http://www.gamedev.net/forum/25-opengl/) look at the right side of the page -->

and there you have it, tons of links.



#3 thelvishow   Members   -  Reputation: 115

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Posted 27 December 2012 - 06:33 AM

As OpenGL version a suggest 3.3+ because almoste all modern graphic card support it and is very similar to OpenGL 4.0.
As GUI library you can use the Qt library.
As math library you can use Eigen (very fast with extensive use of Expression Template and SIMD istruction (SSE, AVX, Neon)).
But you have to learn very well GLSL language. OpenGL is a C API and is not easy to write OOP code. Take a look to (http://oglplus.org/)

Edited by thelvishow, 27 December 2012 - 06:34 AM.


#4 samoth   Crossbones+   -  Reputation: 4783

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Posted 27 December 2012 - 07:13 AM

As OpenGL version a suggest 3.3+ because almoste all modern graphic card support it and is very similar to OpenGL 4.0.
Second this.

Although OpenGL 2.1 is the "equivalent" of DX9, there is no good reason not to use OpenGL 3.x for you (but there are good reasons against using OpenGL 2.x).

Since you come from DX9, you will have to learn a new API in any case, so best learn the "correct" version right away. Otherwise, you'll have to spend extra time at some point int the future on unlearning and re-learning. Going from 3.x to 4.x is a breeze, but there is a huge paradigm cut between 2.x and 3.x.

Edited by samoth, 27 December 2012 - 07:14 AM.


#5 mhagain   Crossbones+   -  Reputation: 7978

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Posted 27 December 2012 - 09:45 AM

I wouldn't quite consider GL2.1 an equivalent of D3D9 - there are some D3D9 features (particularly at the SM3 level - e.g. instancing) that are not available in GL until 3.x, so that seems the most reasonable level to shoot for (particularly if you're using those features!) and I agree with those above recommending it.

 

Regarding choice of shading language, you're on the right track with Cg.  Cg and HLSL are so similar (they were originally more or less the same language) and share so many concepts that it makes sense.


It appears that the gentleman thought C++ was extremely difficult and he was overjoyed that the machine was absorbing it; he understood that good C++ is difficult but the best C++ is well-nigh unintelligible.


#6 mattdesl   Members   -  Reputation: 176

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Posted 29 December 2012 - 12:54 PM

As OpenGL version a suggest 3.3+ because almoste all modern graphic card support it and is very similar to OpenGL 4.0.
As GUI library you can use the Qt library.
As math library you can use Eigen (very fast with extensive use of Expression Template and SIMD istruction (SSE, AVX, Neon)).
But you have to learn very well GLSL language. OpenGL is a C API and is not easy to write OOP code. Take a look to (http://oglplus.org/)

 

GL 3.0+ is still not very widely supported. If you are targeting a casual market, you may want to stick with 2.0 as your target. In this thread it was listed that as few as 51% of Minecraft users supports GL 3.0+. It really comes down to what you need; GL 2 is a fine target for most purposes and can be used in almost the same way as the 3+ programmable pipeline (shaders, custom built-ins, etc). Many drivers will support geometry shaders, FBOs, float textures, etc. through extensions. For example, 93% of drivers support FBO EXT, and it's pretty much a staple in any driver in the last several years. 

 

GL 2.0 and GLSL < 150 is also more compatible with OpenGL ES, so it will prepare you for iOS/Android/WebGL graphics programming.



#7 mhagain   Crossbones+   -  Reputation: 7978

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Posted 02 January 2013 - 06:17 AM

GL 3.0+ is still not very widely supported. If you are targeting a casual market, you may want to stick with 2.0 as your target. In this thread it was listed that as few as 51% of Minecraft users supports GL 3.0+. It really comes down to what you need; GL 2 is a fine target for most purposes and can be used in almost the same way as the 3+ programmable pipeline (shaders, custom built-ins, etc). Many drivers will support geometry shaders, FBOs, float textures, etc. through extensions. For example, 93% of drivers support FBO EXT, and it's pretty much a staple in any driver in the last several years. 

 

GL 2.0 and GLSL < 150 is also more compatible with OpenGL ES, so it will prepare you for iOS/Android/WebGL graphics programming.

 

The OP's engine uses deferred lighting with SM3 so I think we can safely assume that a casual market is not quite the target audience.


It appears that the gentleman thought C++ was extremely difficult and he was overjoyed that the machine was absorbing it; he understood that good C++ is difficult but the best C++ is well-nigh unintelligible.


#8 solenoidz   Members   -  Reputation: 531

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Posted 02 January 2013 - 07:27 AM

Thank you guys. (that doesn't mean I intend to put an end to the thread)

 

I'm using shader model 3.0 because I need vertex texture fetch, VPOS in pixel shaders, more complex programs etc.

 

I guess I can't find a simple tutorial for OpenGL 3.3 deferred lighting with sample source code.

The closest I found is one that deals with OpenGL 2.1 , GLSL 1.2

http://www.codinglabs.net/tutorial_simple_def_rendering.aspx

 

DirectX has SDK with samples, I guess OpenGL has one too and there is a deferred lighting sample. Or maybe nVidia developers zone or AMD samples are my friends.



#9 Acharis   Crossbones+   -  Reputation: 3718

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Posted 02 January 2013 - 04:07 PM

One thing to note, if you want it to be sure all hardware that runs DX9 to run your game you need to limit yourself at most to OpenGL 2.0 :(

 

I have several older comps (DX9) that can run at most OpenGL 2.0 or even OpenGL 1.5 (althrough you can drop that ancient ones). It's especially true for laptops (infamous integrated Intel GPU chips).

Sadly, OpenGL (higher versions) is not that supported (drivers, and if the manufacturer never released drivers for OpenGL higher than 2.0 you can't do anything about it).

 

It's really annoying, these comps do have these capabilities, and are only artificially crippled because of lack of proper drivers. Fortunatelly it does not apply to relatively modern hardware, so if you are ready to abandon some of the older ones you should be fine with OpenGL 3+.


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#10 solenoidz   Members   -  Reputation: 531

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Posted 11 January 2013 - 12:15 AM

Thanks again everyone.
Porting is coming along very nice and I'm happy with the results so far, as the OpenGL version runs faster than D3D, probably due to badly written D3D code on my side or the simplicity of GLSL shaders I use for now. Anyway I have another question.
I have entities which transformation is a D3DXMATRIX and I want to use that matrix for my OpenGL version of the renderer.
I did this already with my D3D view matrix, which is a D3DXMATRIX by multiplying it with a (1,1,-1) scaled matrix


D3DXMatrixScaling(&sca,1,1,-1) ; 
 OGLMatrix = g_Camera->view * sca ;
I load this into OpenGL and it works as a MODEL_VIEW matrix which has the MODEL part identity, so all my meshes lie in origin with no scaling and rotation factors, but I can move the camera around correctly.

Now I need to involve the meshes transform matrices from D3D so they are placed, scaled and rotated in the world, but I'm missing something probably because I get incorrect results.
This doesn't seem to work as expected :



D3DXMatrixScaling(&sca,1,1,-1) ;
  for(int i = 0 ; i < pOGLMeshes.size() ; i++ )
   {       
OGLMatrix = pOGLMeshes[i]->d3dMatrix * g_Camera->view * sca ;
g_pOGLRenderer->RenderMesh(pOGLMeshes[i] , &OGLMatrix[0] ) ;
   }
If I have a D3D model and view matrices, how am I supposed to concatenate them correctly, so I can load them in OpenGL as MODELVIEW matrix ?

Thank you.

Edited by solenoidz, 11 January 2013 - 02:52 AM.


#11 Yours3!f   Members   -  Reputation: 1340

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Posted 11 January 2013 - 04:22 AM

Thanks again everyone.
Porting is coming along very nice and I'm happy with the results so far, as the OpenGL version runs faster than D3D, probably due to badly written D3D code on my side or the simplicity of GLSL shaders I use for now. Anyway I have another question.
I have entities which transformation is a D3DXMATRIX and I want to use that matrix for my OpenGL version of the renderer.
I did this already with my D3D view matrix, which is a D3DXMATRIX by multiplying it with a (1,1,-1) scaled matrix

 

D3DXMatrixScaling(&sca,1,1,-1) ; 
 OGLMatrix = g_Camera->view * sca ;
I load this into OpenGL and it works as a MODEL_VIEW matrix which has the MODEL part identity, so all my meshes lie in origin with no scaling and rotation factors, but I can move the camera around correctly.

Now I need to involve the meshes transform matrices from D3D so they are placed, scaled and rotated in the world, but I'm missing something probably because I get incorrect results.
This doesn't seem to work as expected :



D3DXMatrixScaling(&sca,1,1,-1) ;
  for(int i = 0 ; i < pOGLMeshes.size() ; i++ )
   {       
OGLMatrix = pOGLMeshes[i]->d3dMatrix * g_Camera->view * sca ;
g_pOGLRenderer->RenderMesh(pOGLMeshes[i] , &OGLMatrix[0] ) ;
   }
If I have a D3D model and view matrices, how am I supposed to concatenate them correctly, so I can load them in OpenGL as MODELVIEW matrix ?

Thank you.

d3d:

model * view * projection

ogl:

projection * view * model OR

projection * modelview

 

(reverse order)

This is because OGL uses column major matrices.

http://en.wikipedia.org/wiki/Column-major_order#Column-major_order
related:
http://www.songho.ca/opengl/gl_transform.html



#12 Hodgman   Moderators   -  Reputation: 30386

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Posted 11 January 2013 - 05:32 AM

d3d:
model * view * projection
ogl:
projection * view * model OR
projection * modelview
 
(reverse order)
This is because OGL uses column major matrices.
http://en.wikipedia.org/wiki/Column-major_order#Column-major_order
related:
http://www.songho.ca/opengl/gl_transform.html
 

D3DX uses row-major storage for it's matrices, but by default HLSL uses column-major storage for it's matrices -- the Microsoft Effects framework handles the conversion from one storage method to the other.
GL/GLSL also use column-major storage.

Also, the choice of whether you store your matrices using column-major storage or row-major storage has no effect on your math. This is only a choice of how your perform your 2D array indexing for storage only (at the lowest level of abstraction -- storing items in linear RAM). At the level of abstraction where you're working with mathematical matrices, both methods should behave the same, no matter how their storage mechanism is implemented -- they're both different ways of storing a matrix, there's no such mathematical thing as a row-major matrix or a column-major matrix, just matrices.

The thing that ends up causing you to reverse your mathematics is actually whether you choose to interpret an n-Dimensional vector as a mathematical row-vector (1*n matrix) or a mathematical column-vector (n*1 matrix). Again, in either case the storage mechanism has no effect, your vectors will likely be stored in row-major order, but you can mathematically interpret those bytes as a row-vector or column-vector.

D3DX (and fixed-function D3D) interpret vectors as row-vectors -- so a Float4 becomes a 1-row by 4-column matrix, and mathematically a 1x4 matrix has to be on the left side of a 4x4 matrix when multiplying, which forces you to use that order in your math.

Fixed-function GL interprets vectors as column-vectors -- a 4-row by 1-column matrix, which mathematically has to be on the right side of a 4x4 matrix.

When writing you HLSL/GLSL code, you can choose to use either convention. Shader-based D3D/GL do not force you to use one convention or the other.

Also, as I touched on before, HLSL and GLSL default to using column-major storage for their matrices (and row-major storage for their vectors), but this is just a storage detail, which doesn't affect your math. You can tell HLSL/GLSL to use either storage mechanism, e.g. by using the row_major keyword in HLSL.

 

http://fgiesen.wordpress.com/2012/02/12/row-major-vs-column-major-row-vectors-vs-column-vectors/

http://www.scratchapixel.com/lessons/3d-basic-lessons/lesson-4-geometry/conventions-again-row-major-vs-column-major-vector/



#13 mhagain   Crossbones+   -  Reputation: 7978

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Posted 11 January 2013 - 07:23 AM

Hodgman is correct here - we're not talking about any inner workings of the APIs here and it's incorrect to say that either API uses X; these are just notational conventions and each API is equally capable of either convention.  See http://www.opengl.org/archives/resources/faq/technical/transformations.htm

 

So the reality is that when doing a porting job you can just use the same convention as before and everything will still work - no need to change anything at all as part of the porting job.


It appears that the gentleman thought C++ was extremely difficult and he was overjoyed that the machine was absorbing it; he understood that good C++ is difficult but the best C++ is well-nigh unintelligible.


#14 Yours3!f   Members   -  Reputation: 1340

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Posted 11 January 2013 - 01:39 PM

well, yeah that is the most correct way of saying it.



#15 RobTheBloke   Crossbones+   -  Reputation: 2342

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Posted 11 January 2013 - 02:17 PM


1. GL2.x matches DX9, but it's FUGLY. Go with the GL3/GL4 core spec so that you maintain your sanity.

2. GLEW yes. sdl maybe, unless you already have a WIN32 window up and running, in which case just initialise a GL context in place of the D3D swap chain.

3. Whichever is easiest. I'd probably just stick with GLSL myself....

4. Google around. lighthouse3d had some good GL3 tutorials last time I looked.

5. Just use D3DX maths for everything and upload the matrices to the GLSL shaders. The GL version will need you to (globally) scale everything in the Z axis by -1, and you'll also need to reverse the winding order, but otherwise they'll work the same.



#16 ic0de   Members   -  Reputation: 843

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Posted 12 January 2013 - 12:06 PM

GL 2.x does in fact match Direct3d 9.0 very well there's just a bunch of legacy stuff in it that can probably be ignored. What I do in my engine is use GL 2.1 but in a very opengl 3.x sort of way that way I can run my engine on OpenGL 2.x hardware but also use a core context on 3.x hardware because I don't use the GL 2 features that were removed in version 3.

 

GLEW is great and I use it everywhere and so is SDL.


you know you program too much when you start ending sentences with semicolons;


#17 mhagain   Crossbones+   -  Reputation: 7978

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Posted 12 January 2013 - 02:36 PM

GL2.1 is missing some very important functionality:

  • There is no reasonable render-to-texture API.  You're stuck with using either pbuffers or glCopyTex(Sub)Image2D - the former of which will cause you to want to gnaw your own arms off, the latter of which works well enough but costs some additional performance.
  • No instancing!  I hope you weren't planning on using instancing in your code.
  • There is no reasonable method of updating dynamic buffer objects; if you have any truly dynamic vertex data you may be as well off using old-school client-side arrays with system-memory pointers.
  • There is no explicit specification of attrib locations or uniform locations in your shaders.  This makes shader management a trifle more annoying than it should be.

All of these are present in D3D9, and while they could be pulled into a GL2.1 codebase via extensions, if you're aiming for full GL2.1 compatibility then you're going to need multiple code paths and you're not really just restricting yourself to GL2.1 anymore, are you?

 

So we're clearly in a position where you need to make a tradeoff - do you really want to be inclusive of those with older hardware (and at this stage note that for AMD/ATI and NV we're not just talking about a year or two here; that leaves Intel integrateds) at a high potential cost to your own productivity?


It appears that the gentleman thought C++ was extremely difficult and he was overjoyed that the machine was absorbing it; he understood that good C++ is difficult but the best C++ is well-nigh unintelligible.


#18 solenoidz   Members   -  Reputation: 531

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Posted 14 January 2013 - 01:03 AM

Thanks @mhagain, I needed such a post to compare D3D9 and OpenGL 2.1, as I'm using render to texture, instancing and I'm using dynamic vertex buffers to update my "matrix buffer" used for instancing in D3D.
The reason I'm trying to add OpenGL renderer is to be able to port my applications for Mac and Linux, but more importantly I thought I can make a Web based renderer via WebGL, but I have zero understanding of how a desktop OpenGL simple engine( let's say OGL 2.1) could be ported to WebGL and the user provided with an URL to play applications build with it.

Edited by solenoidz, 14 January 2013 - 01:05 AM.





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