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solenoidz

OpenGL
Porting to OpenGL

16 posts in this topic

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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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.

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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
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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
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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.

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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, [url=http://feedback.wildfiregames.com/report/opengl/feature/GL_EXT_framebuffer_object]93%[/url] 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.

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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.

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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.

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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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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
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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

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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.

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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.

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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.

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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?

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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
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      static PIXELFORMATDESCRIPTOR pfd = // pfd Tells Windows How We Want Things To Be { sizeof(PIXELFORMATDESCRIPTOR), // Size Of This Pixel Format Descriptor 1, // Version Number PFD_DRAW_TO_WINDOW | // Format Must Support Window PFD_SUPPORT_OPENGL | // Format Must Support OpenGL PFD_DOUBLEBUFFER, // Must Support Double Buffering PFD_TYPE_RGBA, // Request An RGBA Format 32, // Select Our Color Depth 0, 0, 0, 0, 0, 0, // Color Bits Ignored 0, // No Alpha Buffer 0, // Shift Bit Ignored 0, // No Accumulation Buffer 0, 0, 0, 0, // Accumulation Bits Ignored 24, // 24Bit Z-Buffer (Depth Buffer) 0, // No Stencil Buffer 0, // No Auxiliary Buffer PFD_MAIN_PLANE, // Main Drawing Layer 0, // Reserved 0, 0, 0 // Layer Masks Ignored }; if (!(hDC = GetDC(windowHandle))) return false; unsigned int PixelFormat; if (!(PixelFormat = ChoosePixelFormat(hDC, &pfd))) return false; if (!SetPixelFormat(hDC, PixelFormat, &pfd)) return false; hRC = wglCreateContext(hDC); if (!hRC) { std::cout << "wglCreateContext Failed!\n"; return false; } if (wglMakeCurrent(hDC, hRC) == NULL) { std::cout << "Make Context Current Second Failed!\n"; return false; } ... // OGL Buffer Initialization glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT); glBindVertexArray(vao); glUseProgram(myprogram); glDrawElements(GL_TRIANGLES, indexCount, GL_UNSIGNED_SHORT, (void *)indexStart); SwapBuffers(GetDC(window_handle));  
    • By Tchom
      Hey devs!
       
      I've been working on a OpenGL ES 2.0 android engine and I have begun implementing some simple (point) lighting. I had something fairly simple working, so I tried to get fancy and added color-tinting light. And it works great... with only one or two lights. Any more than that, the application drops about 15 frames per light added (my ideal is at least 4 or 5). I know implementing lighting is expensive, I just didn't think it was that expensive. I'm fairly new to the world of OpenGL and GLSL, so there is a good chance I've written some crappy shader code. If anyone had any feedback or tips on how I can optimize this code, please let me know.
       
      Vertex Shader
      uniform mat4 u_MVPMatrix; uniform mat4 u_MVMatrix; attribute vec4 a_Position; attribute vec3 a_Normal; attribute vec2 a_TexCoordinate; varying vec3 v_Position; varying vec3 v_Normal; varying vec2 v_TexCoordinate; void main() { v_Position = vec3(u_MVMatrix * a_Position); v_TexCoordinate = a_TexCoordinate; v_Normal = vec3(u_MVMatrix * vec4(a_Normal, 0.0)); gl_Position = u_MVPMatrix * a_Position; } Fragment Shader
      precision mediump float; uniform vec4 u_LightPos["+numLights+"]; uniform vec4 u_LightColours["+numLights+"]; uniform float u_LightPower["+numLights+"]; uniform sampler2D u_Texture; varying vec3 v_Position; varying vec3 v_Normal; varying vec2 v_TexCoordinate; void main() { gl_FragColor = (texture2D(u_Texture, v_TexCoordinate)); float diffuse = 0.0; vec4 colourSum = vec4(1.0); for (int i = 0; i < "+numLights+"; i++) { vec3 toPointLight = vec3(u_LightPos[i]); float distance = length(toPointLight - v_Position); vec3 lightVector = normalize(toPointLight - v_Position); float diffuseDiff = 0.0; // The diffuse difference contributed from current light diffuseDiff = max(dot(v_Normal, lightVector), 0.0); diffuseDiff = diffuseDiff * (1.0 / (1.0 + ((1.0-u_LightPower[i])* distance * distance))); //Determine attenuatio diffuse += diffuseDiff; gl_FragColor.rgb *= vec3(1.0) / ((vec3(1.0) + ((vec3(1.0) - vec3(u_LightColours[i]))*diffuseDiff))); //The expensive part } diffuse += 0.1; //Add ambient light gl_FragColor.rgb *= diffuse; } Am I making any rookie mistakes? Or am I just being unrealistic about what I can do? Thanks in advance
    • By yahiko00
      Hi,
      Not sure to post at the right place, if not, please forgive me...
      For a game project I am working on, I would like to implement a 2D starfield as a background.
      I do not want to deal with static tiles, since I plan to slowly animate the starfield. So, I am trying to figure out how to generate a random starfield for the entire map.
      I feel that using a uniform distribution for the stars will not do the trick. Instead I would like something similar to the screenshot below, taken from the game Star Wars: Empire At War (all credits to Lucasfilm, Disney, and so on...).

      Is there someone who could have an idea of a distribution which could result in such a starfield?
      Any insight would be appreciated
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