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OpenGL I need help from all of you!

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Hello my name is Ryan im 14 years old from Turkey, cheers everyone I started ogl programming a few months ago and i am going good but i have a very serious bug that i am stuck in for 2 months! I have a very simple OpenGL project that is not working right. After looking for info on the Internet, it turns out that the glRotatef() function does the transform local to the object, and does not do a global transform. So the order of operation of is important. In the function Cylinder::ProcessMessage(), processing for the MSG_ROTATE_CURRENT_STATE message, there is an if to check if the rotation is ‘positive’ or ‘negative’ it is just dumb luck that doing the rotations in the backward order works for this program, but to add functionality, I need a function for global rotation. There has to be a function to do global rotation!!! Run the scope project, and press the ‘go’ button. The window has two cylinders, but one of them starts with a view straight-on, so you must use the arrow keys on the keyboard to see one of the cylinders. Can you please help me? I have uploaded source code of the project here: www.albayoung.com/kosta/OGL.zip Please help me!!!!! thank you very much for your time. I owe a very big favour to all who help me :)

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take a breath there kid.
relax,
before trying coding more, since you have all your life ahead of you ( 14 years old ?? ) take some time and study some basic matrix mathematics and then some basic opengl matrix / matrix stack stuff. I guess you are familiar with some opengl concepts but obviously you must master some more before you can say you are stuck because of a bug.
At this point you are, most probably, doing something in a way that you shouldn't.
Pace yourself, study more opengl, before going deep into complex stuff.

you can start from these tutorials here ( http://nehe.gamedev.net )
they are not the best code practices but they have helped a lot of people ( including myself ) to start off.

in the meantime i will take a look of your code ...


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thank you very much skiritis. you cant imagine how much i appreciate it!

I know about nehe and i read tutorials almost every day:)

i am waiting very excited to see if you can help me so i can go past this bug

thanks alot!

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If by global rotation you mean rotate every object, there is a simple solution. You rotate your camera in the opposite way. Still that means you have to do your rotation before drawing your objects in your loop.

Try to understand how OpenGL works,
i)you set your viewpoint(Camera)
ii) Set your transformation for your object(translate/rotate)
iii) draw your object
At this point your object is rasterized, turned to pixels, you can no longer change this object for this frame. Only thing which could happen is another object closer to the camera is rasterized and it overwrites the pixels.

The only 2 ways you could rotate every object in the world are as follows
1) rotate your camera in the opposite direction.
2) apply your rotation calculations to every object in the world.

Obviously the former is easier/faster to do.

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Hello, thanks for the reply

Can you demonstrate me how i can do this in the code that i have provided? My OpenGL knowledge is not very stable and im trying my best to have a sample for the contest entry before 30th... i know im going to take last palce but i just want to do it for my pleasure

thanks alot :)

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Dont really have much time now, but in general, you could do this. Ive not touched Transfomations in a long time so i might be wrong, but i believe it should work.

float[4] globalRotation;

loop every frame
{
glLoadIdentity();
//do this here if you want objects to rotate around camera
//glRotatefv(globalRotation);
for every object
glPushMatrix();
glTranslatef(ObjectPosition)
//do this here if you want objects to around their own axis
//glRotatefv(globalRotation);
glRotatef(localObjectRotation);
//draw your object here
glPopMatrix();
end for

}

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First off, give us some time! You've been stuck on this for 2 months now, you say, so surely you could wait more than 2 hours before bumping your post (say, until it is actually push off the front page?).

Secondly, no one really wants to sort through your entire code base and find the function/section that you are talking about. Can you post that code here directly yourself? You can just copy-and-paste it into a post, and put it between [source] and [/source] tags. Try to give us as little as possible; one or two functions should be enough.

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Thank you for the reply very much. I am sorry for my bad behaviour.

I believe this section of the code needs to be fixed:

bool Cylinder::ProcessMessage(U32 msg, MsgParam param1, MsgParam param2)
{
bool bHandled = false;

switch (msg)
{
case MSG_TRANSLATE_ALONG_LENGTH:
glTranslatef(0.0f, 0.0f, param1.f * m_lfHeight);
bHandled = true;
break;

case MSG_GET_LENGTH:
*(param1.plf) = m_lfHeight;
bHandled = true;
break;

case MSG_ROTATE_CURRENT_STATE:
if (param1.f > 0)
{
glRotatef(m_rotx, param1.f, 0.0f, 0.0f);
glRotatef(m_roty, 0.0f, param1.f, 0.0f);
glRotatef(m_rotz, 0.0f, 0.0f, param1.f);
}
else
{
glRotatef(m_rotz, 0.0f, 0.0f, param1.f);
glRotatef(m_roty, 0.0f, param1.f, 0.0f);
glRotatef(m_rotx, param1.f, 0.0f, 0.0f);
}
bHandled = true;
break;

case MSG_INCR_LENGTH: m_lfHeight++; bHandled = true; break;
case MSG_ACCUM_LENGTH: m_lfHeight += param1.f; bHandled = true; break;
}

if (!bHandled)
bHandled = GLuObj::ProcessMessage(msg, param1, param2);

return bHandled;
}

i want to remove the if statement that checks if rotation is positive

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Quote:
Original post by skiritis
your archive ( OGL ) is broken


thank you very much Skirtis; it appears that u are the only one who bothered to check the source so far... :) i really appreciate it.

I fixed the problem, please try again :)

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Here is a simplified (pseudo code) version of my own drawing function in a flight sim that I am writing. Notice how there is a camera to define how all other objects will be rotated/translated.


int DrawGLScene(GLvoid)
{
glViewport(0, 0, xres, yres);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, x_res/y_res, 1, 10000);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(
camera_position[0],
camera_position[1],
camera_position[2],
camera_direction[0],
camera_direction[1],
camera_direction[2],
0, 1, 0);
glLightfv(GL_LIGHT1, GL_POSITION, your_light);
//Draw all objects here.
draw_world();
return TRUE;
}


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Hey kid [smile] skiritis asked me to help out, so here I am. I can't really understand what your problem is, your explanation is lacking in the question/information respect. However, there are a few things I can point out which may help.

The function ChangeSize, there is no indication as to when that function gets called (apart from the name implying some order), the issue here that it changes the OpenGL state and your rendering function is state sensitive (see below). One option would be to not register ChangeSize with GLUT and manually call it at the beginning of the RenderScene function.

The RenderScene function is state sensitive, that is, the resulting state of OpenGL of the next call to RenderScene is dependent on state just after the current RenderScene call, this is not necessarily a bad thing, but in your case, it looks accidental (because you seem to be tracking absolute rotations using the global variables xRot, yRot and the Visual object's local state variables etc.).

You can make RenderScene self-contained by calling glMatrixMode(GL_MODELVIEW) followed by glLoadIdentity() just before your first call to glPushMatrix in the RenderScene function. After you have done this, try removing the negative check and see if that is the behavior you require.

Hope this helps, I will take another look later tonight.

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Hello everybody & silvermance


Your suggestion did not work.

Look at www.albayoung.com/kosta/OGL2.zip . If you run it, you will see that as the one cylinder moves around, it almost never intersects the other cylinder. This is the wrong behavior. If you run the project from the original post (without your suggested changes, www.albayoung.com/kosta/OGL.zip ) the two cylinders always intersect. This is the correct behavior.

Let me know if you need more details

Once again, thank you all

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I would suggest bumping your thread less frequently as others have suggested, it is hurting your ability to get feedback.

I don’t have as new of a version of Visual Studio so I can’t compile your code. But regardless, slow down and explain a little clearer what your issue is.

By global rotation do you mean the ability to rotate an object around a point rather than rotating it about its own axis? Please explain clearly what you need to do (with an example), and I will try and help you.

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Guest Anonymous Poster
"Scope1" is the first project ( OGL.zip. "Scope2" is the second one (OGL2.zip). The desired behavior of the program is that the two cylinders are always touching - one cylinder stays in the same spot (but grows in length), and one cylinder moves around, but always intersects the other (stationary) cylinder.

1) Run Scope1
2) Press the "Go" button
3) Press the "up arrow" on the keyboard once (now you can see both cylinders)
4) Notice that the two cylinders always intersect

Run the steps above on Scope 2 and you will notice in step 4 that the cylinders don't always intersect.

Hope this helps, Please help me

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Bumping before reading?

As I said in my prior post I am NOT able to compile your code, and with the description you gave I really don’t know much, but here it goes. I really suggest you read what other people post if they are trying to help.

I am going to assume you just want the second cylinder to rotate around the first one.

Code:

DrawCylinder(); //The middle cylinder, drawn at 0,0,0
glPushMatrix();
glTranslatef(); //Translate the distance out the other one is growing minus the second cylinders radius
glRotatef(); //Rotate the cylinder around the center
DrawCylinder(); //The second cylinder, drawn at 0,0,0 (the rotate and transform will move it)
glPopMatrix(); //Done

If that is not what you need, well it is a shame you didn’t give me more details like I asked.

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      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      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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