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Ectara

OpenGL [C] Need help with 3d Rendering Wrapper

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I have a design for a renderer wrapper that is coming along decently, but I became stuck on initialization and destruction of different renderer contexts. The wrapper functions as such:
1. Dynamically load the driver library for a particular renderer.
2. Call the init function found in the library, which fills a renderer structure with function pointers and constants.
3. Use the function pointers and constants.
4. Call the destruction function from the library.

Right now, I support OpenGL and my own software renderer, but the main problem is, OpenGL contexts usually need to be started when the window is created, while my renderer can be initialized at any point. Additionally, my renderer requires a width, height, and pixel format for the display, where my application is currently configured to use SDL for window management; this means that SDL with OpenGL decides its own pixel format, and can't be specified. Also, since OpenGL needs to be enabled in the SDL display creation function, this would make the separation of display and rendering a challenge.

Can anyone advise on this? I've been stuck for a while.

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Personally I'm not understanding the exact question. But what I did was make a base "Renderer" class with virtual functions that can be over written for each seperate renderer. Then just derive your seperate renderers from that. In the code call something like:

if(renderer == "ogl")
lprenderer = new OpenGLRenderer();
else if(renderer == "d3d")
lprenderer = new D3DRenderer();
else
lprenderer = new SoftwareRenderer()

Where each renderer is derived from the main Renderer class with renderer specific functions. I hope that helps or be a little more specific.

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The way I handle it is after creating the window using SDL or whatever, I ask my RendererFactory to create a renderer. All my renderers derive from an abstract interface which at minimum has a Create/Init function which you pass the window height/width and the window handle which in win32 would be the HWND (you can get this from SDL). The window handle argument is just a void* so I can pass whatever into it and the renderer can cast it to whatever it is expecting it to be. You could easily have some kind of Device or WindowParams struct which contains this info and any other generic stuff that a renderer might need to set itself up but I found the minimum to be the 3 I listed above. Having a struct like I mentioned would allow you to easily extend it though.

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@bjz
I suppose it's relevant that I'm using C89, so classes and inheritance aren't quite available. Also, that solution sort of encompasses what I'm already doing. The problems I've presented, are that each renderer requires different data, like the software renderer requiring a width, height, and pixel format, while OpenGL contexts generally have their pixel formats chosen by the window manager, and have the width and height set to the display's dimensions.

Also, the biggest problem, is that OpenGL with SDL needs to be initialized with the display creation. The software renderer needs to be initialized separately, and I was hoping to separate the rendering module and the display module.

@Shael
I suppose I could pass parameters that are ignored, but the problem is, I need to have the OpenGL context created with the SDL window. For D3D, I'm not sure.

Thank you both for the replies.

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I suppose it would be possible to initialize the renderers when the display is initialized, but that's something I was hoping to avoid, as they are separate modules. Any suggestions would be appreciated.

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[quote name='Geri' timestamp='1302974684' post='4799180']
[size="2"][color="#1c2837"]Ectara: for Direct3D, you may can just can simply use TitaniumGL. See the downlad link in my signature.[/color][/size]
[/quote]

Thank you, but this doesn't help my problem. The current wrapper in place would handle Direct3D, OpenGL, my own software renderer, any others added in additional libraries. To remove that entirely, use the OpenGL API, and install an entire extra software renderer would be of no use to me. Also, TitaniumGL supports less platforms than I do.

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What other platforms do you need?

Btw you can create an opengl context any time. But you cant call opengl functions, before you fully init the context (you can manage it with tricks, but i would not do it!)

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[quote name='Geri' timestamp='1302998217' post='4799314']
What other platforms do you need?

Btw you can create an opengl context any time. But you cant call opengl functions, before you fully init the context (you can manage it with tricks, but i would not do it!)
[/quote]

Whichever platforms I decide to support. More accurately, all of the platforms that aren't eliminated for a good reason(This would run poorly on a C64).

SDL requires it to be created at the same time as the display is initialized. See the documentation:
http://sdl.beuc.net/sdl.wiki/SDL_SetVideoMode

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SDL is a crap. I suggest to use native platform initialiastions instead of it. You can get a copy for winapi/Xlib context creation at nehe tutorials. I used glut for a while, but now i throw it out becouse the unlimit numbers of never-fixed-10-year-old bugs. This also stands for SDL.

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[quote name='Geri' timestamp='1303050830' post='4799474']
SDL is a crap. I suggest to use native platform initialiastions instead of it. You can get a copy for winapi/Xlib context creation at nehe tutorials. I used glut for a while, but now i throw it out becouse the unlimit numbers of never-fixed-10-year-old bugs. This also stands for SDL.
[/quote]

SDL works fine for me. Changing every single one of my libraries and abandoning my software renderer to use another is far from an option.

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