I am trying to implement Exponential Shadow Maps and I've got it almost working. The part I am stuck on is the "optional" separable Gaussian blur of the depth map to give soft-looking shadows.
I am using an OpenGL Framebuffer Object attached to a temporary depth map, and I am trying to use a screen quad (two triangles) with the original depth map as an input texture. Then, I am doing the same for the second stage of the blur, with the input and output reversed. Unfortunately, this results in a depth buffer filled with 1.0 which suggests to me that nothing is being drawn.
In this example code I've found, they are using a color and depth attachment in order to draw to a screen quad with a blur shader. (unfortunately the only OpenGL example I could find)
I want to know if this is necessary or that they are only attaching and blurring the color buffer because they are storing their depth values in it.
In other words, I would like to know if it is actually possible to only use a depth buffer Framebuffer Object attachment in this scenario.