Warping with perspective mapping

[402269373]

Hi,

Does anyone know what are the parameters r and q to specify when using NvAPI_GPU_SetScanoutWarping ? For each vertex of the warping mesh, the following values must be specified (in the warping data structure NV_SCANOUT_WARPING_DATA) :
x,y : mesh coordinates per-display rectangle
u,v : texture coordinates in desktop space
r,q : perspective mapping to simulate 3D warp

I know what are the x,y,u,v values but I have no idea what values to specify for r and q.

The only documentation I found about warping is in http://on-demand.gputechconf.com/gtc/2012/presentations/S0322-GTC2012-Warping-Blending-Systems.pdf on slides 20 to 22. An illustration of perspective mapping is in slide 21.
A sample code is in slide 22 :

float vertices[numVerts*6] ={x0,y0,u0,v0,r,q, x1,y1,u1,v1,r,q, …};
NV_SCANOUT_WARPING_DATA warpingData;
warpingData.version = NV_SCANOUT_WARPING_DATA_VER;
warpingData.numVertices = numVerts;
warpingData.vertexFormat = NV_GPU_WARPING_VERTICE_FORMAT_TRIANGLESTRIP_XYUVRQ;
warpingData.vertices = vertices;
warpingData.textureRect = osRect;
int sticky = 0; // output - Reserved field for future use
int maxNumVertices = 0; // output – returns the #pixels at scanout
// This call does the warp
NvAPI_Error error = NvAPI_GPU_SetScanoutWarping(displayId, &warpingData, &maxNumVertices, &sticky);

I will be very happy if anyone can give me a clue about the meaning of these r,q parameters.

[user103025]

have you solved this qustion？ i’m also confused by this.

[chenan.t]

how to solve the r,q parameters?

[nvidia14]

My apologies for only providing a partial solution, but you can find a bit more info on how to calculate the coordinates in this post:

Projective Texture Coordinates and GPU_SetScanoutWarping

Additional testing on different setups showed that the above is not entirely correct. Here’s how NvAPI actually applies the texture coordinates UVRQ: For affine transformations, e.g. bilinear warping, the R-coordinate is zero and the Q-coordinate is one. The UV-coordinates are expressed in desktop coordinates. For perspective transformations, the R-coordinate is still zero, but the Q-coordinate depends on the perspective. I won’t go into details on how to calculate it, as this is part of propr…

To calculate the Q-coordinate, which is not explained in the aforementioned post, you could try solving the 2D homography, code for which can be found here:

Quad warping / homography without opencv

There are easier ways to calculate Q, but as the code is part of proprietary software, I am not allowed to disclose this method.