其中的ovrHmdInfo是VR 头盔（眼镜）相关的一个结构体，包含，分辨率，刷新率，默认分辨率，和水平垂直视野角度。

            ovrFramebuffer_Resolve(frameBuffer);parms.Layers[VRAPI_FRAME_LAYER_TYPE_WORLD].Textures[eye].ColorTextureSwapChain =frameBuffer->ColorTextureSwapChain;parms.Layers[VRAPI_FRAME_LAYER_TYPE_WORLD].Textures[eye].TextureSwapChainIndex =frameBuffer->TextureSwapChainIndex;parms.Layers[VRAPI_FRAME_LAYER_TYPE_WORLD].Textures[eye].TexCoordsFromTanAngles =renderer->TexCoordsTanAnglesMatrix;       //纹理坐标parms.Layers[VRAPI_FRAME_LAYER_TYPE_WORLD].Textures[eye].HeadPose =updatedTracking.HeadPose;ovrFramebuffer_Advance(frameBuffer);

因为要画的是左眼和右眼的画面。所以这里有左右眼对应的数据结构所在的对象params的类型ovrFrameParms：

typedef struct
{// Layers composited in the time warp.ovrFrameLayer                 Layers[VRAPI_FRAME_LAYER_TYPE_MAX];int                                 LayerCount;// Combination of ovrFrameOption flags.int                           WarpOptions;// Which program to run with these layers.ovrFrameProgram               WarpProgram;// Program-specific tuning values.float                         ProgramParms[4];// Application controlled frame index that uniquely identifies this particular frame.// This must be the same frame index that was passed to vrapi_GetPredictedDisplayTime()// when synthesis of this frame started.long long                     FrameIndex;// WarpSwap will not return until at least this many V-syncs have// passed since the previous WarpSwap returned.// Setting to 2 will reduce power consumption and may make animation// more regular for applications that can't hold full frame rate.int                                 MinimumVsyncs;// Latency Mode.ovrExtraLatencyMode           ExtraLatencyMode;// Rotation from a joypad can be added on generated frames to reduce// judder in FPS style experiences when the application framerate is// lower than the V-sync rate.// This will be applied to the view space distorted// eye vectors before applying the rest of the time warp.// This will only be added when the same ovrFrameParms is used for// more than one V-sync.ovrMatrix4f                   ExternalVelocity;// jobject that will be updated before each eye for minimal// latency with VRAPI_FRAME_PROGRAM_MASKED_PLANE_EXTERNAL.// IMPORTANT: This should be a JNI weak reference to the object.// The system will try to convert it into a global reference before// calling SurfaceTexture->Update, which allows it to be safely// freed by the application.jobject                             SurfaceTextureObject;// CPU/GPU performance parameters.ovrPerformanceParms           PerformanceParms;// For handling HMD events and power level state changes.ovrJava                             Java;
} ovrFrameParms;

typedef struct
{// Because OpenGL ES does not support clampToBorder, it is the// application's responsibility to make sure that all mip levels// of the primary eye texture have a black border that will show// up when time warp pushes the texture partially off screen.//CLAMP_TO_BORDER causes OpenGL to only take the border color at the edge of the texture//rather than the average of the border color and texture edge texels.//This allows for a perfect border around the texture.ovrTextureSwapChain *   ColorTextureSwapChain;// The depth texture is optional for positional time warp.ovrTextureSwapChain *   DepthTextureSwapChain;// Index to the texture from the set that should be displayed.int                                 TextureSwapChainIndex;// Points on the screen are mapped by a distortion correction// function into ( TanX, TanY, -1, 1 ) vectors that are transformed// by this matrix to get ( S, T, Q, _ ) vectors that are looked// up with texture2dproj() to get texels.ovrMatrix4f                   TexCoordsFromTanAngles;// Only texels within this range should be drawn.// This is a sub-rectangle of the [(0,0)-(1,1)] texture coordinate range.ovrRectf                      TextureRect;// The tracking state for which ModelViewMatrix is correct.// It is ok to update the orientation for each eye, which// can help minimize black edge pull-in, but the position// must remain the same for both eyes, or the position would// seem to judder "backwards in time" if a frame is dropped.ovrRigidBodyPosef       HeadPose;
} ovrFrameLayerTexture;

static void ovrFramebuffer_SetCurrent(ovrFramebuffer * frameBuffer) {GL(glBindFramebuffer(GL_FRAMEBUFFER,frameBuffer->FrameBuffers[frameBuffer->TextureSwapChainIndex]));
}

static void ovrFramebuffer_Resolve(ovrFramebuffer * frameBuffer) {// Discard the depth buffer, so the tiler won't need to write it back out to memory.const GLenum depthAttachment[1] = { GL_DEPTH_ATTACHMENT };glInvalidateFramebuffer(GL_FRAMEBUFFER, 1, depthAttachment);// Flush this frame worth of commands.glFlush();
}

5.更新交换链

   parms.Layers[VRAPI_FRAME_LAYER_TYPE_WORLD].Textures[eye].ColorTextureSwapChain =frameBuffer->ColorTextureSwapChain;parms.Layers[VRAPI_FRAME_LAYER_TYPE_WORLD].Textures[eye].TextureSwapChainIndex =frameBuffer->TextureSwapChainIndex;parms.Layers[VRAPI_FRAME_LAYER_TYPE_WORLD].Textures[eye].TexCoordsFromTanAngles =renderer->TexCoordsTanAnglesMatrix;       //纹理坐标parms.Layers[VRAPI_FRAME_LAYER_TYPE_WORLD].Textures[eye].HeadPose =updatedTracking.HeadPose;

6.移动到下一帧要使用的交换链索引

static void ovrFramebuffer_Advance(ovrFramebuffer * frameBuffer) {// Advance to the next texture from the set.frameBuffer->TextureSwapChainIndex =(frameBuffer->TextureSwapChainIndex + 1)% frameBuffer->TextureSwapChainLength;
}

每一帧都不停地循环1到6这几个步骤，便实现了，一帧画左眼，一帧画右眼的效果。