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rcapote
New Participant
March 5, 2015

What is wrong with my projection?

I'm working on implementing OVR into my program, but have run into a weird issue where my triangles are being skewed incorrectly. Here is an image to demonstrate:

http://i.imgur.com/FtpGXQ6.png

Without oculus

http://i.imgur.com/lq2PJf1.png

So, the cube is not exact as I'm just holding the HMD to get a screenshot...but generally, when the HMD is horizontal (normal orientation) the cube looks rectangular, and when the HMD is rotated, the cube is more square. Where is my setup incorrect?


// ...

// Setup each eye
        for(ovrEyeType eye = ovrEyeType::ovrEye_Left; eye < ovrEyeType::ovrEye_Count; eye = static_cast<ovrEyeType>(eye+1))
        {
            ovrSizei eyeTextureSize = ovrHmd_GetFovTextureSize(vrHmd, eye, vrHmd->DefaultEyeFov[eye], 1.f); 
            ovrTextureHeader& eyeTextureHeader = _vrContext.eyeTextures[eye].Header;
            eyeTextureHeader.TextureSize = eyeTextureSize;
            eyeTextureHeader.RenderViewport.Size = eyeTextureSize;
            eyeTextureHeader.API = ovrRenderAPI_OpenGL;
        }  

        // ...

        ovrGLConfig cfg;
        cfg.OGL.Header.API = ovrRenderAPI_OpenGL;
        ovrSizei rtsize;
        rtsize.w = _vrContext.resWidth;
        rtsize.h = _vrContext.resHeight;
        cfg.OGL.Header.BackBufferSize = rtsize; 
        cfg.OGL.Header.Multisample = 0;

        int distortionCaps = 0
            | ovrDistortionCap_Vignette
            | ovrDistortionCap_Chromatic
            | ovrDistortionCap_Overdrive
            | ovrDistortionCap_TimeWarp;

        // TODO: Special cases on Linux
    
        int configResult = ovrHmd_ConfigureRendering(vrHmd, &cfg.Config, distortionCaps, vrHmd->DefaultEyeFov, _vrContext.eyeRenderDescs); 

        for(ovrEyeType eye = ovrEyeType::ovrEye_Left; eye < ovrEyeType::ovrEye_Count; eye = static_cast<ovrEyeType>(eye+1))
        {
            const ovrEyeRenderDesc& eyeRenderDesc = _vrContext.eyeRenderDescs[eye];
            // Per Eye projection
            _vrContext.eyeProj[eye] = toGLM(ovrMatrix4f_Projection(vrHmd->DefaultEyeFov[eye], 0.1f, 1024.f, true));

            _vrContext.eyeOffsets[eye] = eyeRenderDesc.HmdToEyeViewOffset;
            
            _vrContext.eyeFbo[eye] = GL::createFrameBuffer(
                _vrContext.eyeTextures[eye].Header.TextureSize.w, _vrContext.eyeTextures[eye].Header.TextureSize.h);

            auto& eyeTextureHeader = _vrContext.eyeTextures[eye];
            ((ovrGLTexture&)eyeTextureHeader).OGL.TexId = _vrContext.eyeFbo[eye].colorBuffer;
        }


View matrix:


return glm::scale(glm::inverse(VR::toGLM(VR::_vrContext.eyePoses[eye])), glm::vec3(OVR_DEFAULT_IPD));

    5 replies

    cybereality
    Inspiring
    March 5, 2015
    This could be an aspect ratio issue, or possibly incorrectly set FOV.
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    jherico
    Inspiring
    March 5, 2015
    Can you show the code where you're actually applying the projection to the rendering? i.e. setting the projection uniform ( or calling glLoadMatrix if you're using the older fixed function pipeline ).
    Brad Davis - Developer for High Fidelity Co-author of Oculus Rift in Action
    rcapoteAuthor
    New Participant
    March 6, 2015
    In my OP the code I posted a clip marked as "view matrix", which is the function called VR::getViewMatrix(eye). I'm currently testing in extended mode, and I default the window size to 1920x1080. Each eye texture is {w=1182 h=1461 }

    In my loop, for each eye I call: 


    glm::mat4 viewMat = VR::getViewMatrix(eye);
    _context.projViewMatrix = VR::_vrContext.eyeProj[eye] * viewMat;


    My function for assigning the view matrix to the shader


    void setUniformMat4(const char* name, glm::mat4 matrix)
    {
        GLuint location = glGetUniformLocation(RenderContext::_context.boundShader.program, name);
        glUniformMatrix4fv(location, 1, GL_FALSE, glm::value_ptr(matrix));
    }
    jherico
    Inspiring
    March 6, 2015
    "rcapote" wrote:

    glm::mat4 viewMat = VR::getViewMatrix(eye);
    _context.projViewMatrix = VR::_vrContext.eyeProj[eye] * viewMat;


    Granted, you can compose the view and projection like this, but most people don't. Particularly when it comes to lighting, it's very important to be able to access the modelview matrix independently of the projection matrix.

    "rcapote" wrote:

    void setUniformMat4(const char* name, glm::mat4 matrix)
    {
        GLuint location = glGetUniformLocation(RenderContext::_context.boundShader.program, name);
        glUniformMatrix4fv(location, 1, GL_FALSE, glm::value_ptr(matrix));
    }


    You might want to try adding some logging or a breakpoint in order to verify that the location being returned isn't -1 (although this seem unlikely as the cause of your error since if it was, you wouldn't see any change in the image as you moved the Rift, since you're putting the view transform in the same matrix).

    What about your vertex shader, what does that look like?
    Brad Davis - Developer for High Fidelity Co-author of Oculus Rift in Action
    rcapoteAuthor
    New Participant
    March 6, 2015
    Vertex shader is nothing special. I currently don't use the TexCoords.


    #version 330

    layout(location=0) in vec4 VertexPosition; 
    layout(location=1) in vec2 UV;
    uniform mat4 uTransformMatrix;
    out vec2 TexCoords;
    out vec4 VertColor;

    void main(void) {
       gl_Position = uTransformMatrix*VertexPosition;
       if(VertexPosition.x > 0) {
            VertColor = vec4(1.f, 0.f, 0.f, 1.f);
       } else {
            VertColor = vec4(0.f, 1.f, 0.f, 1.f);
       } 
       TexCoords = UV;
    }
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