RTW is definitely an eye opener. Though I am not familiar with how to use a warping map, or even create one. Please correct me if I am wrong on something I am about to say.
From what i've gathered so far, using the forward method, a regular shadow map is colored brighter for regions of interest and darker for uninterested regions. I am not sure if the depth channel is colored or another channel. Then this colored shadow map is collapsed to 1D textures. I think all pixels in the same row is summed up to be one pixel in the 1D map, or the brightest color is picked. Then the same for all the pixels on the same column, which is placed in a second 1D texture. These 1D textures are blurred and then they are used to construct a warping map. How this is done, I don't know. Then this warping map is used to render the shadow map once again, this time with regions of interest magnified. And there is the final shadow map. Use this together with the warping map to transform each rendered pixel in view space to the shadow map and check if the depth is greater or not.
The consuming part is to do CPU analysis on the original shadow map and color it, I think. Then maybe (I am guessing) it is possible to collapse the result using the GPU. By rendering the colored shadow map to a render target with 1px height for the columns, and then again to another render target with 1px width for the rows. Gaussian blur on these 1D render targets might also be done I guess. Now, render the warping map(is this a texture?) by sampling each of the 1D textures once for the corresponding pixel. I'm not sure how to use the warping map to mess around in the vertex and pixel shaders....
Am I wrong?