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OpenGL window setup and render, the basic and how to learn them?

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I have a major question here guys and I really need help with it before I can move on. I have a basic C++ understanding and I just bought a opengl book. The problem is that I am having a huge issue understanding what the heck to do. I have spent some time with GLUT so I understand pretty much everything besides window setup. The book I own is Beginning OpenGL Game Programming by Dave Astle and Kevin Hawkins. It was highly recommended to me so I got it. The problem is it seems really complicated. As a noob to opengl is this normal? I was wondering if I could get some tips or something to help me get on the right track. The problem I see with this book is that they only describe 1 out of 12 codes and except you to know the rest. If their is anything I should know or learn please give me a heads up. Thanks [Edited by - snowfell on June 23, 2008 3:50:38 PM]

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When I originally got into OpenGL it took me a while, but what really got me through is the amount of resources online which talk about how to use it. Below are a few resources I used to get me going.

http://nehe.gamedev.net/
http://www.lighthouse3d.com
The forums on this website. :P

Since your just getting into everything GLUT is the best start for getting your environment set up, it's simple in syntax and there are plenty of examples online about how to use it.

I hope this helps.
- Kiro

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Yeah this is normal.
Learning OpenGL is not a walk in the park.
If you learned a simpler 2D API like Allegro or SDL it'd make a lot more sense and click alot faster since you would already have the basic game loop and timing down,etc and only the 3D stuff would be new.

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well I am glad I am not the only one. But guys what are the bare bone things that keep opengl running. Like if a very basic opengl app was split down into pieces, what would they be. Like how do u split up everything into window creation, rendering, timing, and everything else. Let just say I am mostly confused on what is needed to run a opengl app like this.

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The next book you should buy is The Red Book, otherwise known as the OpenGL Programming Guide, The Official Guide to Learning OpenGL, Version <latest>.

It contains all the opengl calls and good descriptions of them. There are good examples, starting from "draw a triangle" and continuing. My copy is dog-eared and ragged, with written remarks in the columns and scotch-tape tabs, etc., etc.

It's the "Bible" of OpenGL.

GLUT helps to keep your attention focused on the basics without worrying about how to get a window built, how to get keyboard input, etc.

Once you get some of the basics and have confidence you know how to draw some basic shapes, learn how to create your own window and use the window procedure for input.

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Quote:
Original post by snowfell
well I am glad I am not the only one. But guys what are the bare bone things that keep opengl running. Like if a very basic opengl app was split down into pieces, what would they be. Like how do u split up everything into window creation, rendering, timing, and everything else. Let just say I am mostly confused on what is needed to run a opengl app like this.


There are any different ways to break up these aspects of an OpenGL application. Below is some pseudo code that can serve as an example of one way it can be done for a simple application.


int main(int argc, char* argv[])
{
//Init GLUT

//Open a GLUT window

//Register you event callbacks with GLUT

//Init anything specific to your game

//Init the game timer with GLUT

//Enter into the GLUT loop

return 0;
}

void timerHandle(void)
{
//Do the per frame game logic, update enemies, check game conditions, ect

//Draw the game

//Register the timer again
}

void keyHandle(char key)
{
//Check what key this is, then react in the needed way
}

void closeWindowHandle()
{
//Clean up anything specific to your game

//Exit the application
exit(0);
}




When the applications starts you set up all the things you need, like a window, your key events, the game timer, ect. Then when you enter into the GLUT main loop your handler functions will be called when the events happen and you react to them as needed.

- Kiro

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Ok I completely read through the chapter on window rendering. I understand what is happening during each step but have no idea of what the structure looks like or how to uses what I learned there in my own program. The way the source code is written it very narrow minded and makes it difficult to take things (ideas and such things, not literally taking things) from it. I have a notebook and I filled about 4 pages just from skimming over that chapter.

What I figured out (correct me if I am wrong) about OpenGL structure is that in most cases it is broken down into:
-a function for pixel format
-window procedure
-window main
-enabling OpenGL
-disabling OpenGL

Library's for most OpenGL applications are:
-windows.h (or whatever other platform you use)
-gl.h
-glu.h (not required)

While reading I learned a bit about WGLs but I don't see how they fit into a program. I mean I know that they are used to setup OpenGL on windows with commands like wglCreateContext() but I don't see what to do with it. I know a little bit about rendering context and device context but yet again don't know how to use them in a program.

My question is, now that I have these very bare bone things sorted out what would be the next wise step to adding some function to a very basic OpenGL program.

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If you're using windows, read through:

http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=01

as mentioned by KiroNeem.

It has a complete setup and explains each step.

As an aside, windows.h, gl.h and glu.h are header files, not libraries. The header files tell the compiler how to format the function calls.

The compiler itself knows nothing about libraries.

The linker takes the compiled code and provides the proper calls to the libraries, which must also be specified in your project properties.

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I'm in the situation as same as you. I read some windows program's source, read some book about windows programming, and I try to write a lot of windows code to understand the windows program how to work, hope this can help you.

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So would a quick study of win32 help? All I no is someone told me that win32 was unimportant for opengl. If looking at that may help resolve confusion I guess I will give it a try. Are their any good win32 tutorials or links out there?

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Well the first 2 chapters are all windows setup and stuff. If you just get a basic openGL setup, then you should be fine. From there its draw triangle, rotate it, light it, texture it. The books goes in nice steps.

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Quote:
Original post by snowfell
The problem I see with this book is that they only describe 1 out of 12 codes and except you to know the rest.

The book's main focus, according to the title, is on OpenGL game programming - not C++ and Win32 programming. Perhaps your general programming prowess isn't quite up to the level the book is targetting. Then again, I haven't read it [smile].

An overview of a typical Win32/OpenGL setup process is this:

Win32 Stuff
1) Create a window class (WNDCLASSEX) instance and register it (RegisterClassEx). N.B. This holds a pointer to the WndProc procedure (the window's event handler).

2) Create a window (CreateWindowEx) to retrieve a HWND handle.

3) If you that to go fullscreen then create a DEVMOVE instance and use it select a screen resolution by calling ChangeDisplaySettings. Otherwise, if you want to keep it windowed, skip this step.

4) Retrieve a device context using the window's handle with the GetDC function.

5) Create a pixel format descriptor (PIXELFORMATDESCRIPTOR) and use it to find a compatible pixel format using ChoosePixelFormat.

6) Set this pixel format to the window device using SetPixelFormat.

WGL Stuff
7) Create an OpenGL rendering context from the window's device using wglCreateContext.

8) Set this context as the one to use, with: wglMakeCurrent.

Making it visible
9) Now the window is all setup and ready to use; unless you said otherwise, the window is hidden by default, so call ShowWindow to make it visible.

OpenGL stuff
It's all ready to go, OpenGL provides default values for everything. You do normally configure different things though, like matrices, texturing etc. I won't go into this as it's all dependant on what exactly you want to do.

Shutting down
1) Return the resolution to normal if you changed it for fullscreen mode: ChangeDisplaySettings(NULL, 0);

2) Release the rendering context: wglMakeCurrent(NULL, NULL);

3) Delete the rendering context: wglDeleteContext( hRC );

4) Release the device context: ReleaseDC(hWnd, hDC);

5) Kill the window: DestroyWindow(hWnd);

6) I also like to unregister the window class at the end of the application (UnregisterClass), but it's superfluous.

And with any luck, I got all that right; hope it helps clear things up.

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snowfell ignore win32 seriously
use something like SDL to setup the window+handle input etc

arguments for

A/ its easier
B/ its crossplatform (just read support now for nintendoDS + iphone)
C/ its stable
D/ its welltested on 1000s machines

arguments against

A/ if youre not doing a game u may want more control
B/ anything else??

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      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
      DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
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