# DX11 Picking in DX11

## Recommended Posts

Hello,

I'm trying to make picking working following this tutorial: http://www.rastertek.com/dx11tut47.html

I'm not sure is it me or the author confuses spaces at the end of this tutorial? Can someone have a fresh look at this? Namely he states that multyplying vector by inverse view matrix we get the result in view space. Shouldn't it be in world space? And then we go from world into object space and there make final test? His ray intersection doesn't take into account sphere position so final test looks like it's in object space, but he also says it's in world space... So yeah, thoughts?

Edited by keym

##### Share on other sites

As far as I understand things, a typical view matrix is actually a "inverted" in the sense that if the camera matrix is in the world space, then the required matrix to transform things from world space to the camera's space is actually "inverse camera matrix" or the view matrix or inverse view matrix in this case... to make things complicated. It is just a case of "confusing naming". I use naming "camera matrix" to define camera's location and direction in world space and view matrix is actually the inverted camera matrix.

You can confirm this from many code samples where the view matrix is constructed. Just rarely the code uses the actual matrix inversion, since in the view matrix case the inverse can be calculated easily.

Yes, in the code the the ray is transformed to the local/object space by the inverse world matrix of the sphere. The beauty of things is that in the local space the sphere is located at origo (0,0,0) so translation doesn't have to be accounted in the ray-sphere intersection test.

The advantage of this technique is that it supports also things like scaling / non-uniform scaling for the world matrix. The ray-sphere test remains always the same, since it's just the ray's position and direction changing.

Cheers!

Edited by kauna

##### Share on other sites

Well... shouldn't this be that simple:

object space ----[world a.k.a. model matrix]----> world space

world space ----[view a.k.a. camera matrix]----> view space

view space ----[projection matrix]----> clip space

object space <----[inverse world a.k.a. model matrix]---- world space

world space <----[inverse view a.k.a. camera matrix]---- view space

view space <----[inverse projection matrix]---- clip space

?

Anyways, this is how it *seems right* to me, but I'm not a guru here. Maybe I'm being picky ;) about naming and that was not the intention of this topic (but still I wanted to clarify naming before I ask my question(s) and make more confusion).

So, the reason I post is because (obviously) I have a problem with picking. The issue here is that in my renderer I use right hand coordinate system, like in OpenGL (for sake of compatibility, I have OGL renderer in this app too and I don't want to negate every needed value to get the same result, it would only make more future errors).

So I construct my projection matrix using D3DXMatrixPerspectiveFovRH() and view matrix using D3DXMatrixLookAtRH(). Before sending them to HLSL I transpose them (for some reason I have to do this, otherwise I get incorrect results [DX stores matrices in row major, but in HLSL they need to be in column major?]). All is sweet and dandy until picking occurs. I'm pretty sure that I'm doing something wrong, because this is my first attempt with renderer independent picking. I follow what's in the tutorial but intersection test gives incorrect results. For sake of simplicity my sphere is at (0,0,0) so I don't have to care about world and invWorld matrices. I'm guessing that something is wrong with my matrices but it's hard to track down.

Also I'm not sure what's going on here (tutorial):

// Adjust the points using the projection matrix to account for the aspect ratio of the viewport.
m_D3D->GetProjectionMatrix(projectionMatrix);
pointX = pointX / projectionMatrix._11;
pointY = pointY / projectionMatrix._22;


and how exactly the unprojecting part works. I mean I have mouse coordinates that I rescale into -1, 1 range but how do I get from vec2 to vec3? Where does the 3rd component come from?

##### Share on other sites

Solved.

Looks like all my math was ok but I forgot one thing - my rendering WinAPi control has an offset in x,y (cause I have sidebar and other stuff on the side) and I forgot to take that into account when reading mouse position over the viewport. For instance I got [0,0] at the origin of the window, not the rendering control. Now all works well. Thanks for looking.

## Create an account

Register a new account

• ### Forum Statistics

• Total Topics
628300
• Total Posts
2981900
• ### Similar Content

• Does buffer number matter in ID3D11DeviceContext::PSSetConstantBuffers()? I added 5 or six constant buffers to my framework, and later realized I had set the buffer number parameter to either 0 or 1 in all of them - but they still all worked! Curious why that is, and should they be set up to correspond to the number of constant buffers?
Similarly, inside the buffer structs used to pass info into the hlsl shader, I added padding inside the c++ struct to make a struct containing a float3 be 16 bytes, but in the declaration of the same struct inside the hlsl shader file, it was missing the padding value - and it still worked! Do they need to be consistent or not? Thanks.
struct CameraBufferType
{
XMFLOAT3 cameraPosition;
};

• I'm attempting to implement some basic post-processing in my "engine" and the HLSL part of the Compute Shader and such I think I've understood, however I'm at a loss at how to actually get/use it's output for rendering to the screen.
Assume I'm doing something to a UAV in my CS:
RWTexture2D<float4> InputOutputMap : register(u0); I want that texture to essentially "be" the backbuffer.

I'm pretty certain I'm doing something wrong when I create the views (what I think I'm doing is having the backbuffer be bound as render target aswell as UAV and then using it in my CS):

DXGI_SWAP_CHAIN_DESC scd; ZeroMemory(&scd, sizeof(DXGI_SWAP_CHAIN_DESC)); scd.BufferCount = 1; scd.BufferDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM; scd.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT | DXGI_USAGE_SHADER_INPUT | DXGI_USAGE_UNORDERED_ACCESS; scd.OutputWindow = wndHandle; scd.SampleDesc.Count = 1; scd.Windowed = TRUE; HRESULT hr = D3D11CreateDeviceAndSwapChain(NULL, D3D_DRIVER_TYPE_HARDWARE, NULL, NULL, NULL, NULL, D3D11_SDK_VERSION, &scd, &gSwapChain, &gDevice, NULL, &gDeviceContext); // get the address of the back buffer ID3D11Texture2D* pBackBuffer = nullptr; gSwapChain->GetBuffer(0, __uuidof(ID3D11Texture2D), (LPVOID*)&pBackBuffer); // use the back buffer address to create the render target gDevice->CreateRenderTargetView(pBackBuffer, NULL, &gBackbufferRTV); // set the render target as the back buffer CreateDepthStencilBuffer(); gDeviceContext->OMSetRenderTargets(1, &gBackbufferRTV, depthStencilView); //UAV for compute shader D3D11_UNORDERED_ACCESS_VIEW_DESC uavd; ZeroMemory(&uavd, sizeof(uavd)); uavd.Format = DXGI_FORMAT_R8G8B8A8_UNORM; uavd.ViewDimension = D3D11_UAV_DIMENSION_TEXTURE2D; uavd.Texture2D.MipSlice = 1; gDevice->CreateUnorderedAccessView(pBackBuffer, &uavd, &gUAV); pBackBuffer->Release();
After I render the scene, I dispatch like this:
gDeviceContext->OMSetRenderTargets(0, NULL, NULL); m_vShaders["cs1"]->Bind(); gDeviceContext->CSSetUnorderedAccessViews(0, 1, &gUAV, 0); gDeviceContext->Dispatch(32, 24, 0); //hard coded ID3D11UnorderedAccessView* nullview = { nullptr }; gDeviceContext->CSSetUnorderedAccessViews(0, 1, &nullview, 0); gDeviceContext->OMSetRenderTargets(1, &gBackbufferRTV, depthStencilView); gSwapChain->Present(0, 0); Worth noting is the scene is rendered as usual, but I dont get any results from the CS (simple gaussian blur)
I'm sure it's something fairly basic I'm doing wrong, perhaps my understanding of render targets / views / what have you is just completely wrong and my approach just makes no sense.

If someone with more experience could point me in the right direction I would really appreciate it!

On a side note, I'd really like to learn more about this kind of stuff. I can really see the potential of the CS aswell as rendering to textures and using them for whatever in the engine so I would love it if you know some good resources I can read about this!

Thank you <3

P.S I excluded the .hlsl since I cant imagine that being the issue, but if you think you need it to help me just ask

P:P:S. As you can see this is my first post however I do have another account, but I can't log in with it because gamedev.net just keeps asking me to accept terms and then logs me out when I do over and over

• I was wondering if anyone could explain the depth buffer and the depth stencil state comparison function to me as I'm a little confused
So I have set up a depth stencil state where the DepthFunc is set to D3D11_COMPARISON_LESS, but what am I actually comparing here? What is actually written to the buffer, the pixel that should show up in the front?
I have these 2 quad faces, a Red Face and a Blue Face. The Blue Face is further away from the Viewer with a Z index value of -100.0f. Where the Red Face is close to the Viewer with a Z index value of 0.0f.
When DepthFunc is set to D3D11_COMPARISON_LESS the Red Face shows up in front of the Blue Face like it should based on the Z index values. BUT if I change the DepthFunc to D3D11_COMPARISON_LESS_EQUAL the Blue Face shows in front of the Red Face. Which does not make sense to me, I would think that when the function is set to D3D11_COMPARISON_LESS_EQUAL the Red Face would still show up in front of the Blue Face as the Z index for the Red Face is still closer to the viewer
Am I thinking of this comparison function all wrong?
Vertex data just in case
//Vertex date that make up the 2 faces Vertex verts[] = { //Red face Vertex(Vector4(0.0f, 0.0f, 0.0f), Color(1.0f, 0.0f, 0.0f)), Vertex(Vector4(100.0f, 100.0f, 0.0f), Color(1.0f, 0.0f, 0.0f)), Vertex(Vector4(100.0f, 0.0f, 0.0f), Color(1.0f, 0.0f, 0.0f)), Vertex(Vector4(0.0f, 0.0f, 0.0f), Color(1.0f, 0.0f, 0.0f)), Vertex(Vector4(0.0f, 100.0f, 0.0f), Color(1.0f, 0.0f, 0.0f)), Vertex(Vector4(100.0f, 100.0f, 0.0f), Color(1.0f, 0.0f, 0.0f)), //Blue face Vertex(Vector4(0.0f, 0.0f, -100.0f), Color(0.0f, 0.0f, 1.0f)), Vertex(Vector4(100.0f, 100.0f, -100.0f), Color(0.0f, 0.0f, 1.0f)), Vertex(Vector4(100.0f, 0.0f, -100.0f), Color(0.0f, 0.0f, 1.0f)), Vertex(Vector4(0.0f, 0.0f, -100.0f), Color(0.0f, 0.0f, 1.0f)), Vertex(Vector4(0.0f, 100.0f, -100.0f), Color(0.0f, 0.0f, 1.0f)), Vertex(Vector4(100.0f, 100.0f, -100.0f), Color(0.0f, 0.0f, 1.0f)), };
• By mellinoe
Hi all,
First time poster here, although I've been reading posts here for quite a while. This place has been invaluable for learning graphics programming -- thanks for a great resource!
Right now, I'm working on a graphics abstraction layer for .NET which supports D3D11, Vulkan, and OpenGL at the moment. I have implemented most of my planned features already, and things are working well. Some remaining features that I am planning are Compute Shaders, and some flavor of read-write shader resources. At the moment, my shaders can just get simple read-only access to a uniform (or constant) buffer, a texture, or a sampler. Unfortunately, I'm having a tough time grasping the distinctions between all of the different kinds of read-write resources that are available. In D3D alone, there seem to be 5 or 6 different kinds of resources with similar but different characteristics. On top of that, I get the impression that some of them are more or less "obsoleted" by the newer kinds, and don't have much of a place in modern code. There seem to be a few pivots:
The data source/destination (buffer or texture) Read-write or read-only Structured or unstructured (?) Ordered vs unordered (?) These are just my observations based on a lot of MSDN and OpenGL doc reading. For my library, I'm not interested in exposing every possibility to the user -- just trying to find a good "middle-ground" that can be represented cleanly across API's which is good enough for common scenarios.
Can anyone give a sort of "overview" of the different options, and perhaps compare/contrast the concepts between Direct3D, OpenGL, and Vulkan? I'd also be very interested in hearing how other folks have abstracted these concepts in their libraries.

• If I do a buffer update with MAP_NO_OVERWRITE or MAP_DISCARD, can I just write to the buffer after I called Unmap() on the buffer? It seems to work fine for me (Nvidia driver), but is it actually legal to do so? I have a graphics device wrapper and I don't want to expose Map/Unmap, but just have a function like void* AllocateFromRingBuffer(GPUBuffer* buffer, uint size, uint& offset); This function would just call Map on the buffer, then Unmap immediately and then return the address of the buffer. It usually does a MAP_NO_OVERWRITE, but sometimes it is a WRITE_DISCARD (when the buffer wraps around). Previously I have been using it so that the function expected the data upfront and would copy to the buffer between Map/Unmap, but now I want to extend functionality of it so that it would just return an address to write to.

• 9
• 9
• 11
• 10
• 10