I'm using Java OpenGL (JOGL 2.x, built from Git source). I'm rendering my scene to a framebuffer object with a color and a depth attachment. I'd like to convert the [0,1] depth buffer values into world-space distances. My depth attachment is defined as follows:
private void setupDepthFBOs(GL2 gl,
int width,
int height,
int[] frameBufferIds,
int[] colorBufferIds,
int[] depthBufferIds) {
// based on
// http://www.java2s.com/Code/Java/Advanced-Graphics/BloomOpenGL.htm
// generate a framebuffer object
gl.glGenFramebuffers(1, frameBufferIds, 0);
// bind the framebuffer
gl.glBindFramebuffer(GL.GL_FRAMEBUFFER, frameBufferIds[0]);
// generate a texture in memory
gl.glGenTextures(1, colorBufferIds,0);
gl.glBindTexture(GL2.GL_TEXTURE_2D, colorBufferIds[0]);
// this will be an RGBA texture (4 bpp) with width, height..
gl.glTexImage2D(GL2.GL_TEXTURE_2D, // target texture type
0, // mipmap LOD level
GL2.GL_RGBA8, // internal pixel format
width, // width of generated image
height, // height of generated image
0, // border of image
GL2.GL_RGBA, // external pixel format
GL2.GL_UNSIGNED_BYTE, // datatype for each value
null); // buffer to store the texture in memory
// set some texture parameters?
gl.glTexParameteri(GL.GL_TEXTURE_2D,
GL.GL_TEXTURE_MIN_FILTER, GL.GL_LINEAR);
// use the texture we just created in the framebuffer we just created
gl.glFramebufferTexture2D(
GL2.GL_FRAMEBUFFER, // target texture type
GL.GL_COLOR_ATTACHMENT0, // attachment point
GL.GL_TEXTURE_2D, // texture target type
colorBufferIds[0], // on-gpu id for texture
0); // mipmap lod level
gl.glGenTextures(1,depthBufferIds,0);
gl.glBindTexture(GL.GL_TEXTURE_2D,depthBufferIds[0]);
gl.glTexImage2D(GL2.GL_TEXTURE_2D, // target texture type
0, // mipmap LOD level
GL2.GL_DEPTH_COMPONENT24, // internal pixel format
//GL2.GL_DEPTH_COMPONENT
width, // width of generated image
height, // height of generated image
0, // border of image
GL2.GL_DEPTH_COMPONENT, // external pixel format
GL2.GL_UNSIGNED_INT, // datatype for each value
null); // buffer to store the texture in memory
gl.glTexParameteri(GL.GL_TEXTURE_2D,
GL.GL_TEXTURE_MIN_FILTER, GL.GL_NEAREST);
gl.glTexParameteri(GL.GL_TEXTURE_2D,
GL.GL_TEXTURE_MAG_FILTER, GL.GL_NEAREST);
gl.glTexParameteri(GL.GL_TEXTURE_2D,
GL.GL_TEXTURE_WRAP_S, GL.GL_CLAMP_TO_EDGE);
gl.glTexParameteri(GL.GL_TEXTURE_2D,
GL.GL_TEXTURE_WRAP_T, GL.GL_CLAMP_TO_EDGE);
gl.glFramebufferTexture2D(GL.GL_FRAMEBUFFER,
GL.GL_DEPTH_ATTACHMENT,
GL.GL_TEXTURE_2D,
depthBufferIds[0],0);
gl.glBindTexture(GL.GL_TEXTURE_2D, 0);
int status = gl.glCheckFramebufferStatus(GL2.GL_FRAMEBUFFER);
if (status == GL2.GL_FRAMEBUFFER_COMPLETE) {
gl.glBindFramebuffer(GL.GL_FRAMEBUFFER, 0);
} else {
throw new IllegalStateException("Frame Buffer Object not created. Status was: " + status);
}
}
This successfully creates a depth buffer, which I can read as a texture and render to the screen, or use as input to a shader (my intended eventual use case).
After some discussions on the IRC a few nights ago, I came up with the following formula relating the Projection Matrix (denoted here as p) and depth-buffer value to the distance to each point on screen in world-space:
z = (p_33)/(p_34 + depth)
(note: my projection matrix/eye is set up looking in the Z+ direction)
This produces almost-sane z-values, but there's a significant margin of error between the distance to known points in the scene, and the value returned by this equation.
Any ideas what I might be doing wrong here?
