Jump to content
  • Advertisement
Sign in to follow this  
Quat

DX11 Copying MSAA depth buffer dx11

This topic is 2476 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

I am using DX11.

I am using the light prepass system, where I first render the view space normals and depth to a render target. This pass also lays down the scene depth, so there is no overdraw in later passes.

Now for MSAA, I was going to use non-msaa render targets and depth buffers for generating the g-buffer and screen space light map, and just use MSAA for the final pass. However, with this I need two depth buffers--one multisampled for the back buffer, and one not multisampled for the g-buffer. So my question is if there is a way to avoid drawing the scene depth twice.

I don't think I can use MSAA g-buffer because that would average depths at the edges.

Is it possible to have two render targets where one is multisampled and the other is not? I am thinking of having something like (g-buffer and non-multisampled depth buffer) and (null render target with multisampled depth buffer).

Share this post


Link to post
Share on other sites
Advertisement
Not using MSAA for the G-Buffer pass will give you really bad artifacts. You will end up having lighting information for a completely different triangle applied to subsamples for edge triangles during your second geometry pass. Or if no triangle was rendered at all to a pixel during the G-Buffer pass and a subsample samples lighting from that texel, it will get black because there will be no lighting there at all.\

If you really want to avoid artifacts, you have to do it like this:

1. Render G-Buffer with MSAA
2. Render lighting with MSAA, making sure you individually light subsamples for triangle edges
3. Render your second geometry pass, making sure to sample the right subsample from the lighting buffer for edge triangles

It sucks pretty badly from an implementation and performance point of view, and it's one of the big reasons that I really don't like light prepass.

Anyway to answer your question...all render targets and depth stencil buffers need to have the same MSAA mode when you're rendering. You can't have one of them with MSAA, and one of them without. You can render a depth buffer with MSAA and manually resolve it using a pixel shader if you want.

Share this post


Link to post
Share on other sites
OK, I read the ShaderX7 article on Deferred Shading and MSAA and I see what you mean.

I would like to confirm some things:

1. If I create a MSAA back buffer and depth buffer, I must enable D3D11_RASTERIZER_DESC::MultisampleEnable so that the system will automatically resolve the back buffer before presenting. I need to test this again, but I seem to recall getting antialiasing even if I didn't enable this state, as long as I created a MSAA back buffer and depth buffer.

2. MSAA textures are never resolved automatically (you must call ResolveSubresource). To sample a MSAA texture at the sample level, you must use Load(texCoord, sampleIndex).

3. For a pixel shader to run at sample frequency, you must have input SV_SAMPLEINDEX.

4. Use SV_Coverage to detect edges, so that we only run the pixel shader per sample about the edge.


Also, what do you like instead of light prepass? Just full deferred renderer?

Share this post


Link to post
Share on other sites
1. The setting in the rasterizer state doesn't have anything to do with resolving the render target. It actually controls how MSAA is handled during rasterization. The documentation that explains it is here and here, although it can be a bit confusing if you're not familiar with how MSAA works. Basically what happens when you disable that is that you have multiple subsamples in your render target, but the rendering will occur as if it were a non-multisampled render target.

2. Yes, these are both correct. You must also declare your texture as a Texture2DMS to be able to load subsamples (you will get a warning from the debug layer if you don't, or if you try to use a Texture2DMS with a non-multisampled texture).

3. Yes, you must declare it and use it in your shader program. Alternatively, you can also use the "sample" modifier on one of your pixel shader inputs to get the shader to run per-sample. This modifier causes the input to he interpolated to each MSAA sample point, rather than the pixel center.

4. SV_Coverage is a great way to detect edge pixels. You can also use it as an output, to control which subsamples get written by the pixel shader.

I prefer a full deferred renderer. IMO light prepass is only really worth it on platforms where multiple render targets aren't available, or are too expensive.


OK, I read the ShaderX7 article on Deferred Shading and MSAA and I see what you mean.

I would like to confirm some things:

1. If I create a MSAA back buffer and depth buffer, I must enable D3D11_RASTERIZER_DESC::MultisampleEnable so that the system will automatically resolve the back buffer before presenting. I need to test this again, but I seem to recall getting antialiasing even if I didn't enable this state, as long as I created a MSAA back buffer and depth buffer.

2. MSAA textures are never resolved automatically (you must call ResolveSubresource). To sample a MSAA texture at the sample level, you must use Load(texCoord, sampleIndex).

3. For a pixel shader to run at sample frequency, you must have input SV_SAMPLEINDEX.

4. Use SV_Coverage to detect edges, so that we only run the pixel shader per sample about the edge.


Also, what do you like instead of light prepass? Just full deferred renderer?

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Popular Now

  • Advertisement
  • Similar Content

    • By cozzie
      Hi all,
      It's been a while since I've been working on my HLSL shaders, and found out I'm not 100% sure if I'm applying gamma correctness correctly. So here's what I do:
      - create backbuffer in this format: DXGI_FORMAT_R8G8B8A8_UNORM_SRGB
      - source textures (DDS) are always in SRGB format
      - this way the textures should be gamma correct, because DX11 helps me out here
      Now my question is about material and light colors. I'm not sure if I need to convert those to linear space. The colors are handpicked on screen, so I guess gamma correct. Below are 2 screenshots, the darker is including converting those colors (``return float4(linearColor.rgb * linearColor.rgb, linearColor.a);``), in the lighter shot I didn't do this conversion.
      These are the properties of the brick material and the light source (there are no other lightsources in the scene, also no global ambient):
      Material:
      CR_VECTOR4(0.51f, 0.26f, 0.22f, 1.0f), // ambient CR_VECTOR4(0.51f, 0.26f, 0.22f, 1.0f), // diffuse RGB + alpha CR_VECTOR4(0.51f, 0.26f, 0.22f, 4.0f)); // specular RGB + power Directional light:
      mDirLights[0].Ambient = CR_VECTOR4(0.1f, 0.1f, 0.1f, 1.0f); mDirLights[0].Diffuse = CR_VECTOR4(0.75f, 0.75f, 0.75f, 1.0f); mDirLights[0].Specular = CR_VECTOR4(1.0f, 1.0f, 1.0f, 16.0f); mDirLights[0].Direction = CR_VECTOR3(0.0f, 1.0f, 0.0f);
      So in short, should I or should I not do this conversion in the lighting calculation in the shader? (and/or what else are you seeing :))
      Note that I don't do anything with the texture color, after it's fetched in the shader (no conversions), which I believe is correct.
       


    • By chiffre
      Introduction:
      In general my questions pertain to the differences between floating- and fixed-point data. Additionally I would like to understand when it can be advantageous to prefer fixed-point representation over floating-point representation in the context of vertex data and how the hardware deals with the different data-types. I believe I should be able to reduce the amount of data (bytes) necessary per vertex by choosing the most opportune representations for my vertex attributes. Thanks ahead of time if you, the reader, are considering the effort of reading this and helping me.
      I found an old topic that shows this is possible in principal, but I am not sure I understand what the pitfalls are when using fixed-point representation and whether there are any hardware-based performance advantages/disadvantages.
      (TLDR at bottom)
      The Actual Post:
      To my understanding HLSL/D3D11 offers not just the traditional floating point model in half-,single-, and double-precision, but also the fixed-point model in form of signed/unsigned normalized integers in 8-,10-,16-,24-, and 32-bit variants. Both models offer a finite sequence of "grid-points". The obvious difference between the two models is that the fixed-point model offers a constant spacing between values in the normalized range of [0,1] or [-1,1], while the floating point model allows for smaller "deltas" as you get closer to 0, and larger "deltas" the further you are away from 0.
      To add some context, let me define a struct as an example:
      struct VertexData { float[3] position; //3x32-bits float[2] texCoord; //2x32-bits float[3] normals; //3x32-bits } //Total of 32 bytes Every vertex gets a position, a coordinate on my texture, and a normal to do some light calculations. In this case we have 8x32=256bits per vertex. Since the texture coordinates lie in the interval [0,1] and the normal vector components are in the interval [-1,1] it would seem useful to use normalized representation as suggested in the topic linked at the top of the post. The texture coordinates might as well be represented in a fixed-point model, because it seems most useful to be able to sample the texture in a uniform manner, as the pixels don't get any "denser" as we get closer to 0. In other words the "delta" does not need to become any smaller as the texture coordinates approach (0,0). A similar argument can be made for the normal-vector, as a normal vector should be normalized anyway, and we want as many points as possible on the sphere around (0,0,0) with a radius of 1, and we don't care about precision around the origin. Even if we have large textures such as 4k by 4k (or the maximum allowed by D3D11, 16k by 16k) we only need as many grid-points on one axis, as there are pixels on one axis. An unsigned normalized 14 bit integer would be ideal, but because it is both unsupported and impractical, we will stick to an unsigned normalized 16 bit integer. The same type should take care of the normal vector coordinates, and might even be a bit overkill.
      struct VertexData { float[3] position; //3x32-bits uint16_t[2] texCoord; //2x16bits uint16_t[3] normals; //3x16bits } //Total of 22 bytes Seems like a good start, and we might even be able to take it further, but before we pursue that path, here is my first question: can the GPU even work with the data in this format, or is all I have accomplished minimizing CPU-side RAM usage? Does the GPU have to convert the texture coordinates back to a floating-point model when I hand them over to the sampler in my pixel shader? I have looked up the data types for HLSL and I am not sure I even comprehend how to declare the vertex input type in HLSL. Would the following work?
      struct VertexInputType { float3 pos; //this one is obvious unorm half2 tex; //half corresponds to a 16-bit float, so I assume this is wrong, but this the only 16-bit type I found on the linked MSDN site snorm half3 normal; //same as above } I assume this is possible somehow, as I have found input element formats such as: DXGI_FORMAT_R16G16B16A16_SNORM and DXGI_FORMAT_R16G16B16A16_UNORM (also available with a different number of components, as well as different component lengths). I might have to avoid 3-component vectors because there is no 3-component 16-bit input element format, but that is the least of my worries. The next question would be: what happens with my normals if I try to do lighting calculations with them in such a normalized-fixed-point format? Is there no issue as long as I take care not to mix floating- and fixed-point data? Or would that work as well? In general this gives rise to the question: how does the GPU handle fixed-point arithmetic? Is it the same as integer-arithmetic, and/or is it faster/slower than floating-point arithmetic?
      Assuming that we still have a valid and useful VertexData format, how far could I take this while remaining on the sensible side of what could be called optimization? Theoretically I could use the an input element format such as DXGI_FORMAT_R10G10B10A2_UNORM to pack my normal coordinates into a 10-bit fixed-point format, and my verticies (in object space) might even be representable in a 16-bit unsigned normalized fixed-point format. That way I could end up with something like the following struct:
      struct VertexData { uint16_t[3] pos; //3x16bits uint16_t[2] texCoord; //2x16bits uint32_t packedNormals; //10+10+10+2bits } //Total of 14 bytes Could I use a vertex structure like this without too much performance-loss on the GPU-side? If the GPU has to execute some sort of unpacking algorithm in the background I might as well let it be. In the end I have a functioning deferred renderer, but I would like to reduce the memory footprint of the huge amount of vertecies involved in rendering my landscape. 
      TLDR: I have a lot of vertices that I need to render and I want to reduce the RAM-usage without introducing crazy compression/decompression algorithms to the CPU or GPU. I am hoping to find a solution by involving fixed-point data-types, but I am not exactly sure how how that would work.
    • By cozzie
      Hi all,
      I was wondering it it matters in which order you draw 2D and 3D items, looking at the BeginDraw/EndDraw calls on a D2D rendertarget.
      The order in which you do the actual draw calls is clear, 3D first then 2D, means the 2D (DrawText in this case) is in front of the 3D scene.
      The question is mainly about when to call the BeginDraw and EndDraw.
      Note that I'm drawing D2D stuff through a DXGI surface linked to the 3D RT.
      Option 1:
      A - Begin frame, clear D3D RT
      B - Draw 3D
      C - BeginDraw D2D RT
      D - Draw 2D
      E - EndDraw D2D RT
      F - Present
      Option 2:
      A - Begin frame, clear D3D RT + BeginDraw D2D RT
      B - Draw 3D
      C - Draw 2D
      D - EndDraw D2D RT
      E- Present
      Would there be a difference (performance/issue?) in using option 2? (versus 1)
      Any input is appreciated.
    • By Sebastian Werema
      Do you know any papers that cover custom data structures like lists or binary trees implemented in hlsl without CUDA that work perfectly fine no matter how many threads try to use them at any given time?
    • By cozzie
      Hi all,
      Last week I noticed that when I run my test application(s) in Renderdoc, it crashes when it enable my code that uses D2D/DirectWrite. In Visual Studio no issues occur (debug or release), but when I run the same executable in Renderdoc, it crashes somehow (assert of D2D rendertarget or without any information). Before I spend hours on debugging/ figuring it out, does someone have experience with this symptom and/or know if Renderdoc has known issues with D2D? (if so, that would be bad news for debugging my application in the future );
      I can also post some more information on what happens, code and which code commented out, eliminates the problems (when running in RenderDoc).
      Any input is appreciated.
  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

Participate in the game development conversation and more when you create an account on GameDev.net!

Sign me up!