integrate Oculus SDK Distortion within simple DirectX Engine - directx

Question

I was working some time on a very simple DirectX11 Render Engine. Today I managed to Setup Stereo Rendering (Rendering the Scene twice into textures) for my Oculus Rift integration.
[Currently]
So what I am basically doing currently is:
I have a 1280 x 800 Window
render the whole scene into the RenderTargetViewLeft_ (1280 x 800)
render the content of RenderTargetViewLeft_ as a "EyeWindow" (like in the tutorial) to the left side of the Screen (640 x 800)
render the whole Scene into the RenderTargetViewRight_ (1280 x 800)
render the content of RenderTargetViewRight_ as a "EyeWindow" (like in the tutorial) to the right side of the Screen (640 x 800)
so all of this works so far, I got the Scene rendered twice into seperate Textures, ending up in a Splitscreen.
[DirectX11 Render Loop]
bool GraphicsAPI::Render()
{
bool result;
// [Left Eye] The first pass of our render is to a texture now.
result = RenderToTexture(renderTextureLeft_);
if (!result)
{
return false;
}
// Clear the buffers to begin the scene.
BeginScene(0.0f, 0.0f, 0.0f, 1.0f);
// Turn off the Z buffer to begin all 2D rendering.
TurnZBufferOff();
// Render The Eye Window orthogonal to the screen
RenderEyeWindow(eyeWindowLeft_, renderTextureLeft_);
// Turn the Z buffer back on now that all 2D rendering has completed.
TurnZBufferOn();
// [Right Eye] ------------------------------------
result = RenderToTexture(renderTextureRight_);
if (!result)
{
return false;
}
TurnZBufferOff();
RenderEyeWindow(eyeWindowRight_, renderTextureRight_);
TurnZBufferOn();
// [End] Present the rendered scene to the screen.
EndScene(); // calls Present
return true;
}
[What I want to do now]
Now I am trying to achieve a Barrel Distortion with the Oculus SDK. Currently I am not concerning about a different virtual camera for the second Image, just want to achieve the Barrel distortion for now.
I have read the Developers Guide [1] and also tried to look into the TinyRoom Demo, but I don't understand completely what's necessary now to achieve the distortion with the SDK in my already working DirectX Engine.
In Developers Guide Render Texture Initialization, they show how to create a texture for the API. I guess it means, I need to setup ALL my RendertargetViews with the according API size (Render Targets are currently sized 1280 x 800) - and even change the DepthStencilView and Backbuffer sice aswell I guess.
The render-loop would look something like this then:
ovrHmd_BeginFrame(hmd, 0);
BeginScene(0.0f, 0.0f, 0.0f, 1.0f);
...
// Render Loop as the Code above
...
ovrHmd_EndFrame(hmd, headPose, EyeTextures);
// EndScene(); // calls Present, not needed on Oculus Rendering
I feel something's missing so I am sure I don't got all that right.
[Update]
So, i achieve to Render the Scene with barrel Distortion using the Oculus API. Though the polygon of the left- and right image are too far seperated, but this could be caused by using my default 1280 x 800 Texture Size for the Render Targets. The CameraStream seems aswell not rendered orthogonal to the Screen when moving the HMD. Gonna do some further testing ;)
[1] - Oculus Developers Guide: https://developer.oculus.com/documentation/

Answer 1

The key Point of an 3d HMD Support is generally to render the whole graphics Scene twice. Once with the left virtual camera, and once with the right virtual camera - the "eye" distance between them varies, but it's approximaetly about 65mm.
To store the Scene, one has to render the graphic Scene to textures. I have rendered my Scene first using my left virtual camera into a RenderTextureLeft_, and afterwards I have rendered the exact same Scene with my right virtual camera into a RenderTextureRight_. This technique is called "render to texture". This means we save the Image for further post processing stuff into a separate Texture instead of rendering it directly into the backbuffer to Display on the Monitor.
So well, but how can we render to the Oculus Rift now? It's important to set up an hmd instance and configure it correctly first. This is really good explained here in the official docs [1]: https://developer.oculus.com/documentation/pcsdk/latest/concepts/dg-render/
After both RenderTextures (left eye, right eye) are successfully rendered into textures and the oculus device has been configured accordingly, one needs to supply the Oculus SDK with both of the rendered Textures to print them on the hmd's Monitor and doing the Barrel distortion using the Oculus SDK (not the Client distortion which is no longer supported in the newer SDK Versions).
Here I am showing my DirectX code which supplys the oculus sdk with both of my renderetextures and doing also the Barrel distortion:
bool OculusHMD::RenderDistortion()
{
ovrD3D11Texture eyeTexture[2]; // Gather data for eye textures
Sizei size;
size.w = RIFT_RESOLUTION_WIDTH;
size.h = RIFT_RESOLUTION_HEIGHT;
ovrRecti eyeRenderViewport[2];
eyeRenderViewport[0].Pos = Vector2i(0, 0);
eyeRenderViewport[0].Size = size;
eyeRenderViewport[1].Pos = Vector2i(0, 0);
eyeRenderViewport[1].Size = size;
eyeTexture[0].D3D11.Header.API = ovrRenderAPI_D3D11;
eyeTexture[0].D3D11.Header.TextureSize = size;
eyeTexture[0].D3D11.Header.RenderViewport = eyeRenderViewport[0];
eyeTexture[0].D3D11.pTexture = graphicsAPI_->renderTextureLeft_->renderTargetTexture_;
eyeTexture[0].D3D11.pSRView = graphicsAPI_->renderTextureLeft_->GetShaderResourceView();
eyeTexture[1].D3D11.Header.API = ovrRenderAPI_D3D11;
eyeTexture[1].D3D11.Header.TextureSize = size;
eyeTexture[1].D3D11.Header.RenderViewport = eyeRenderViewport[1];
eyeTexture[1].D3D11.pTexture = graphicsAPI_->renderTextureRight_->renderTargetTexture_;
eyeTexture[1].D3D11.pSRView = graphicsAPI_->renderTextureRight_->GetShaderResourceView();
ovrHmd_EndFrame(hmd_, eyeRenderPose_, &eyeTexture[0].Texture);
return true;
}
The presentation of the Stereo Image including the Barrel distortion as Kind of a post processing effect is finally done via this line:
ovrHmd_EndFrame(hmd_, eyeRenderPose_, &eyeTexture[0].Texture);
Hopefully the code helps the one or other to understand the Pipeline better.