# OpenGL Implementing linear-z.

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I am trying to do this at the moment, but running into a couple of problems. My current implemention: I divide the z-column of the projection matrix by z Far:
proj.m33/=camera->getFarPlane();
proj.m43/=camera->getFarPlane();


My shaders all calculate the final vertex position like so:
float4 applyModelViewProj(float3 vpos, float4x4 modelViewProj)
{
float4 OUTposition = mul(modelViewProj, float4(vpos, 1.0));
OUTposition.z = OUTposition.z * OUTposition.w;
return OUTposition;
}


This article was my source for this technique, but it is directed at DirectX users. I think OpenGL does things a little differently with the z-coordinates but I can't find out how. The visual manifestation of the problem I am getting is that it seems that depth is not being correctly interpolated between vertices, and also depth seems to increase again behind the camera. Could anybody please explain to me the OpenGL specific method of doing a linear z-buffer?

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EDIT While I believe that the principles mentioned herein are correct, there are some mistakes made by me, namely some sign errors. In a post furthur below I correct this. /EDIT

I don't know the solution directly, but I know that OpenGL actually does handle linear perspective projection differently. The following is what I think gives the solution, but please check it double. I'm also not sure about any side effects. If you try it out please let me know what happens ...

If using glFrustum, then the last 2 rows of the projection matrix are
[ 0  0  (f+n)/(n-f)  2fn/(n-f) ][ 0  0       -1          0     ]
When multiplying this with an arbitray vertex position [ x y z 1 ]T and normalizing the result, then
z' := (f+n)/(f-n) - 2fn/(f-n)/z
is the transformed z. So, the limits are
z'(z=n) = -1
z'(z=f) = +1

In D3D the equivalent stuff is (see matrix in the cited article)
z' := f/(f-n) - fn/(f-n)/z
and hence the limits are
z'(z=n) = 0
z'(z=f) = +1
as is affirmed by the article. The trick was to alter the z' formula by dividing by f and multiplying by z, so that
z" := z'*z/f = z/(f-n) - n/(f-n)
and the limits are still
z"(z=n) = 0
z"(z=f) = +1

Now you're doing the same in OpenGL, yielding in
z" := z*(f+n)/(f-n)/f - 2n/(f-n)
with the limits
z"(z=n) = -n/f > -1
z"(z=f) = +1

Since z clipping is done on [-1,+1] but z''(z=n) is approx. 0, you'll have geometry located before the near "clipping" plane visible.

What you want instead is a linear function
z"(z) := a*z + b
that fulfills OpenGL's limits. That leads to 2 functions
z"(z=n) = a*n + b == -1
z"(z=f) = a*f + b == +1
what can be solved to
a = 2/(f-n)
b = -(n+f)/(f-n)
so that
z" = 2z/(f-n) - (n+f)/(f-n)

Dividing by w=-z and comparing the co-efficients with OpenGL's matrix values shows that
proj.m33 = -a
proj.m43 = -b
would produce the correct matrix.

Oh well, I hope that I made no mistake :)

[Edited by - haegarr on May 27, 2008 3:44:27 AM]

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Or alternativaly, create a GL_RGBA32F render to texture and output the eye space depth values

varying vec4 myvertex;

myvertex = ModelviewMatrix * gl_Vertex;

varying vec4 myvertex;

gl_FragColor = myvertex;

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Or even more alternatively output the eyespace.z / farplane. This will give you a value ranging from 0 to 1, as the farplane is the maximum value that an eyespace z value can have.

The other way is to just convert the value into a linear value when you need it in the shader (this will allow you to use the existing depth buffer).

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Quote:
 Original post by stramitOr even more alternatively output the eyespace.z / farplane. This will give you a value ranging from 0 to 1, as the farplane is the maximum value that an eyespace z value can have.The other way is to just convert the value into a linear value when you need it in the shader (this will allow you to use the existing depth buffer).

Can you explain this a bit deeper, please? IMHO that is what the OP / cited article primarily did, isn't it? And it doesn't work for the OP because he is using OpenGL. The projection is a mapping from the eye space to the clip space, and OpenGL's clip space doesn't range from 0 to +1 but from -1 to +1. The article explains using the z buffer and driving as little as possible additional shader operations as goals. So, following your approach would waste half of the range of the z buffer and requires an additional clipping plane, or else adds more operations to be done for each vertex, didn't it?. Please disprove this point if I'm wrong.

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Quote:
 Original post by AshkanLinearized Depth Using Vertex Shaders

Well, if you would please take the time to read at least the OP, then you'll see that exactly the cited article was implemented and doesn't work "as is" for OpenGL. This entire thread is about to adapt the method to work well with OpenGL.

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I thought that a GL matrix was transposed (notationally, if not in memory layout) with respect to a Direct3D matrix. So to modify this technique for OpenGL, shouldn't it be the 33 & 34 elements that are modified, rather than 33 and 43?

After all, if a point in GL is a column vector, then row 3 of a GL matrix is what determines Z'. This implies that to linearize Z', you need to modify elements on the 3rd row, possibly in the way that haegarr is suggesting.

Or am I being a noob?

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Quote:
 Original post by twedukI thought that a GL matrix was transposed (notationally, if not in memory layout) with respect to a Direct3D matrix. So to modify this technique for OpenGL, shouldn't it be the 33 & 34 elements that are modified, rather than 33 and 43?

Thanks for hinting at this point. Yep, mathematically the matrices of OpenGL are the transposed matrices of D3D. To be precise, OpenGL uses column vectors while D3D uses row vectors. Additionally, the (2D) matrices have also a memory layout when stored in the (1D) linear memory. Here OpenGL uses the column major order, while D3D uses the row major order. In sum, column vectors with column major order and row vectors with row major order yield in the identical layout of matrices in memory. There is no need to re-arrange matrix values when switching from the one form to the other. (Opposed to that, e.g. COLLADA uses column vectors and row major order, and hence requires re-arrangement when using with either OpenGL or D3D.)

Quote:
 Original post by twedukAfter all, if a point in GL is a column vector, then row 3 of a GL matrix is what determines Z'. This implies that to linearize Z', you need to modify elements on the 3rd row, ...

Yep a 2nd time. I haven't proven which elements m33 and m43 are by looking into D3D docs, but concluded from the math in the cited article that the both scalars are those also affected in OpenGL matrix. For clarification, I meant the substitution
[ 0  0  a  b ]
for the 3rd row.

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Quote:
Original post by haegarr
Quote:
 Original post by twedukI thought that a GL matrix was transposed (notationally, if not in memory layout) with respect to a Direct3D matrix. So to modify this technique for OpenGL, shouldn't it be the 33 & 34 elements that are modified, rather than 33 and 43?

Thanks for hinting at this point. Yep, mathematically the matrices of OpenGL are the transposed matrices of D3D. To be precise, OpenGL uses column vectors while D3D uses row vectors. Additionally, the (2D) matrices have also a memory layout when stored in the (1D) linear memory. Here OpenGL uses the column major order, while D3D uses the row major order. In sum, column vectors with column major order and row vectors with row major order yield in the identical layout of matrices in memory. There is no need to re-arrange matrix values when switching from the one form to the other. (Opposed to that, e.g. COLLADA uses column vectors and row major order, and hence requires re-arrangement when using with either OpenGL or D3D.)

I'm not totally sure which elements m33 and m43 are when speaking of D3D, but concluded from the math in the cited article that the both scalars are those also affected in OpenGL matrix. For clarification, I meant the substitution
[ 0  0   a  b ][ 0  0  -1  0 ]
for the 3rd and 4th rows.

The 4,3 element of a D3D matrix is row 4, column 3. So depending on the memory layout of 'proj', it's possible that the OP is clobbering the -1 element rather than setting the element with value 'b'.

To OP: how is 'proj' defined?

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What happens if you don't do the projection matrix trick and use the original code of:
finalPosition.z = finalPosition.z * finalPosition.w / farClipDistance;

This way you don't need any messy matrix tricks.

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Quote:
 Original post by agi_shiWhat happens if you don't do the projection matrix trick and use the original code of:finalPosition.z = finalPosition.z * finalPosition.w / farClipDistance;This way you don't need any messy matrix tricks.

From a theoretical point of view: It wouldn't work in general since it would violate OpenGL's depth clipping range. As a result you'll get geometry behind the camera become visible.

Here is the reason: The depth range in camera co-ordinates is from near clipping distance n up until far clipping distance f, hence [n,f]. Dividing these by f normalizes this range to [n/f,1] with n/f close to 0 since f>>n normally. But OpenGL clips in the range [-1,1] (as opposed to D3D which clips in [0,1] as it seems to be). That means in reverse that the depth range [-f,n/f] (in camera space) will accidentally also be visible.

The "matrix trick" is just a way to overcome this problem by virtually mapping [n,f] linearly to [-f,f], and that with minimal additional computations. Of course, one can do the same trick directly in the shader, but pays then with more runtime consumption. One can otherwise add another clipping plane, but pays then with loss of half of the depth buffer resolution.

Unfortunately, it seems that bluntman doesn't visit this thread very often, or else isn't answering due to any other reason, so someone else need to verify the theory. Perhaps I can spend some time to do so tomorrow.

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Oh, thanks for clearing it up [smile]. I was a bit confused as to how things worked.

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haegarr your method works!! The clip plane is in the correct place, everything works as expected.
Now comes the obvious.. The close and far depth resolution seems good, but I could do with more mid distance resolution!! I will try to work out how to implement my own depth fall off function, but any hints would be appriciated! I think I at least have more understanding of how the projection works in relation to the z-buffer now, thanks for the help everybody!

/edit
I spoke to soon! When I tried splitting my view frustum into near and far again I noticed it is not working quite right, just trying to work out the problem now.

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Quote:
Original post by haegarr
Quote:
 Original post by AshkanLinearized Depth Using Vertex Shaders

Well, if you would please take the time to read at least the OP, then you'll see that exactly the cited article was implemented and doesn't work "as is" for OpenGL. This entire thread is about to adapt the method to work well with OpenGL.

I sincerely apologize. I guess today is one of those days when everything I say or do just turns out wrong. Kind of makes me wonder what's next...

[Edited by - Ashkan on May 26, 2008 9:07:24 PM]

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Well I'm trying to work through the math myself and can't seem to get the correct results:
haegarr you wrote:
z' := (f+n)/(f-n) - 2fn/(f-n)/z
as the default OpenGL transform after normalisation, but shouldn't the (f-n) bits still be (n-f)?
If I understand correctly it should be (without simplification):
z' := [z(f+n)/(n-f) + 2fn/(n-f)]/z
This is correct yes? I have been working through this calculation using the near plane expecting to get z'=-1 for when z=n but it doesn't seem to be working:
e.g:
n = 0.1
f = 1000
z = n = 0.1
z' = [0.1x(1000+0.1)/(0.1-1000) + 2x1000x0.1/(0.1-1000)]/-0.1
= (-0.1x1000.1/999.9 - 200/999.9)/-0.1
= (-0.10002 - 0.20002)/-0.1
= ~3
What am I missing?!

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This morning it comes to my mind that I've forgotten that OpenGL's camera looks along the negative z axis. The near and far clipping distances as specified in glFrustum are positive values, but when used as co-ordinates in camera space they are to be negative. Hence, actually the clipping range is restricted by -n and -f. (I apologize not remembering this earlier.)

If the above conclusion is true, then the projection of z
z" = (f+n)/(f-n) + 2fn/(f-n)/z
will produce
z"(z=-n) = -1
z"(z=-f) = +1
at the limits. That is nice so far.

Still wanting a linear function
a*z+b
that fulfills OpenGL's clipping, we now get
z"(z=-n) = -a*n + b == -1
z"(z=-f) = -a*f + b == +1
what yields in
a = -2/(f-n)
b = -(f+n)/(f-n)
when being resolved. This differs in the sign of co-efficient a in comparison to my previous attempt.

Fitting the co-efficients into the matrix would yield in
[ 0 0 2/(f-n) (f+n)/(f-n) ]
for the 3rd row.

@bluntman: Does this match the problem you've observed?

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Quote:
 Original post by bluntmanWell I'm trying to work through the math myself and can't seem to get the correct results:haegarr you wrote:z' := (f+n)/(f-n) - 2fn/(f-n)/zas the default OpenGL transform after normalisation, but shouldn't the (f-n) bits still be (n-f)?If I understand correctly it should be (without simplification):z' := [z(f+n)/(n-f) + 2fn/(n-f)]/zThis is correct yes? I have been working through this calculation using the near plane expecting to get z'=-1 for when z=n but it doesn't seem to be working:e.g:n = 0.1f = 1000z = n = 0.1z' = [0.1x(1000+0.1)/(0.1-1000) + 2x1000x0.1/(0.1-1000)]/-0.1 = (-0.1x1000.1/999.9 - 200/999.9)/-0.1 = (-0.10002 - 0.20002)/-0.1 = ~3What am I missing?!

You've hit the sign problem I've mentioned in my previous post (to be correct, its an outcome of that problem). While the rows of the projection matrix in my first post were okay, I've made a mistake then during making a stand-alone equation of it. The correct formula would be
z' := ( (f+n)/(n-f)*z + 2fn/(n-f) ) / ( -z ) = (f+n)/(f-n) + 2fn/(f-n)/z
Notice please that the 4th row of the matrix contains a "minus 1", so that division by -z is done. I then incorporated the sign into the denominators.

EDIT: Please bear in mind that I make all this on a pure theoretical basis. Err, well, one can say also that I want you do the beta testing ;) So you're absolutely right to check my writings...

[Edited by - haegarr on May 27, 2008 3:37:11 AM]

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Thanks alot for the help so far haergarr! The revised equations do appear to work correctly (I switched their signs and multiply by w in the vertex shader), the clip planes are in the correct places now, both near and far.
I have run into another problem though: the interpolation between vertices of the depth value does not seem to be linear with depth! I guess it could be an accuracy problem, I am using a 32bit depth buffer, but shaders under some profiles perform calculations at 24 bit iirc. That said, my shaders are running on the Cg gp4 profile, which I would guess has 32bit floats at least!
I tweaked my shader to output the final (projected, normalized) value of z/w + 1.0 to visualise the values being used in the z buffer and this is the result I got:

The banding is not compression artifacts, it is the 24bit color output from the vertex shader, you can see how the bands are distorted. They run across a perfect sphere of quads so should appear smooth.
If I rotate the camera further to the left:

You can see another mesh that should be behind the grey sphere is starting to show through where the interpolation is becoming most distorted. The mesh that is showing through is more highly tesselated, therefore its interpolations are less distorted relative to the sphere's.
Heres a shot from close to the surface (I have upped the contrast to make the problem obvious):

You can see the boundaries of the polygons, and how the z/w value is NOT being interpolated linearly with respect to actual depth!
Any ideas? Is this one of the problems the non-linear z buffer is meant to overcome? Is the math still not quite right?

edit/
Arg! I think I might have just worked out the problem: it occured to me when I went back to look at the last image, that the relation between the image colors and depth is only correct if the color is interpolated in the same manner as the depth. I figure one interpolation is much the same as the next, but I guess OpenGL seperately interpolates each element of the projected v (v') and then performs the z/w per pixel to get the normalized value. I have subverted that by multiplying the z by w at the vertex stage. Interpolating z'w is not the same as interpolating z' and w seperately then multiplying (by RHW):
e.g. (my rough workings to prove that to myself!)
za = 0.1 zb = 0.2
wa = 5 wb = 100
za*wa = 0.5
zb*wb = 20
i = interpolation (0 <= i <= 1) = 0.5
interp( zawa zbwb i ) = (20 - 0.5) * 0.5 + 0.5 = 9.75 + 0.5 = 10.25 <<<<
interp( za zb i ) = (0.2 - 0.1) * 0.5 + 0.1 = 0.15
interp( wa wb i ) = (100 - 5) * 0.5 + 5 = 47.5 + 5 = 52.5
== 52.5 * 0.15 = 7.875 <<<<

If this is the problem then I can't immediately see how to fix it :/

[Edited by - bluntman on May 27, 2008 5:23:05 AM]

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When I read the original article, it made me wonder what effect the linearized Z would have on the GPU's perspective correction.

Is linearized Z really compatible with how a GPU does perspective correction? I must admit that I haven't bothered to go through the math, but I would have thought not.

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Well I thought I would update this for future searchers. Neither haegarr nor myself have come up with a simple solution for the non-linear interpolation problem. In the end I have resorted to setting the depth values myself via the fragment shader, which works fine.

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Introduction
Graphics APIs have come a long way from small set of basic commands allowing limited control of configurable stages of early 3D accelerators to very low-level programming interfaces exposing almost every aspect of the underlying graphics hardware. Next-generation APIs, Direct3D12 by Microsoft and Vulkan by Khronos are relatively new and have only started getting widespread adoption and support from hardware vendors, while Direct3D11 and OpenGL are still considered industry standard. New APIs can provide substantial performance and functional improvements, but may not be supported by older hardware. An application targeting wide range of platforms needs to support Direct3D11 and OpenGL. New APIs will not give any advantage when used with old paradigms. It is totally possible to add Direct3D12 support to an existing renderer by implementing Direct3D11 interface through Direct3D12, but this will give zero benefits. Instead, new approaches and rendering architectures that leverage flexibility provided by the next-generation APIs are expected to be developed.
There are at least four APIs (Direct3D11, Direct3D12, OpenGL/GLES, Vulkan, plus Apple's Metal for iOS and osX platforms) that a cross-platform 3D application may need to support. Writing separate code paths for all APIs is clearly not an option for any real-world application and the need for a cross-platform graphics abstraction layer is evident. The following is the list of requirements that I believe such layer needs to satisfy:
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Render device (IRenderDevice  interface) is responsible for creating all other objects (textures, buffers, shaders, pipeline states, etc.).
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TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); If native API supports multithreaded resource creation, textures and buffers can be created by multiple threads simultaneously.
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PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
// Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
// Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
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:
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 tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
Atmospheric scattering sample 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, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.

• Good Evening,
I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
First of I was thinking about all those shapes which I need will need for debugging purposes: circles, rectangles, lines, polygons.
I am really stucked right now because of the fundamental question:
Where do I store my vertices positions for each line (object)? Currently I am not using a model matrix because I am using orthographic projection and set the final position within the VBO. That means that if I add a new line I would have to expand the "points" array and re-upload (recall glBufferData) it every time. The other method would be to use a model matrix and a fixed vbo for a line but it would be also messy to exactly create a line from (0,0) to (100,20) calculating the rotation and scale to make it fit.
If I proceed with option 1 "updating the array each frame" I was thinking of having 4 draw calls every frame for the lines vao, polygons vao and so on.
In addition to that I am planning to use some sort of ECS based architecture. So the other question would be:
Should I treat those debug objects as entities/components?
For me it would make sense to treat them as entities but that's creates a new issue with the previous array approach because it would have for example a transform and render component. A special render component for debug objects (no texture etc) ... For me the transform component is also just a matrix but how would I then define a line?
Treating them as components would'nt be a good idea in my eyes because then I would always need an entity. Well entity is just an id !? So maybe its a component?
Regards,
LifeArtist
• By QQemka
Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
Let's go:
Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
There were several more but i forgot/solved them at time of writing
• By RenanRR
Hi All,
I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
#version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);
So, some doubts:
- Why use it like that?
- Is it okay to manipulate the camera that way?
-in this way, are not the vertex's positions that changes instead of the camera?
- I need to pass MVP to all shaders of object in my scenes ?

What it seems, is that the camera stands still and the scenery that changes...
it's right?

Thank you

• Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

int rgbValue = int(textureSample.w);//4 bytes of data packed as color
// algorithm might not be correct and endianness might need switching.
vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
extractedData /= 255.0f;