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POOmnidirectional shadow mapping with depth cubemap
 

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  1. POOmnidirectional shadow mapping with depth cubemap
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    <p>I'm working with omnidirectional point lights. I already implemented shadow mapping using a cubemap texture as color attachement of 6 framebuffers, and encoding the light-to-fragment distance in each pixel of it.</p> <p>Now I would like, if this is possible, to change my implementation this way:</p> <ul> <li>1) attach a depth cubemap texture to the depth buffer of my framebuffers, instead of colors.</li> <li>2) render depth only, do not write color in this pass</li> <li>3) in the main pass, read the depth from the cubemap texture, convert it to a distance, and check whether the current fragment is occluded by the light or not.</li> </ul> <p>My problem comes when converting back a depth value from the cubemap into a distance. I use the light-to-fragment vector (in world space) to fetch my depth value in the cubemap. At this point, I don't know which of the six faces is being used, nor what 2D texture coordinates match the depth value I'm reading. Then how can I convert that depth value to a distance?</p> <p>Here are snippets of my code to illustrate:</p> <p>Depth texture:</p> <pre><code>glGenTextures(1, &amp;TextureHandle); glBindTexture(GL_TEXTURE_CUBE_MAP, TextureHandle); for (int i = 0; i &lt; 6; ++i) glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_DEPTH_COMPONENT, Width, Height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); </code></pre> <p>Framebuffers construction:</p> <pre><code>for (int i = 0; i &lt; 6; ++i) { glGenFramebuffers(1, &amp;FBO-&gt;FrameBufferID); glBindFramebuffer(GL_FRAMEBUFFER, FBO-&gt;FrameBufferID); glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, TextureHandle, 0); glDrawBuffer(GL_NONE); } </code></pre> <p>The piece of fragment shader I'm trying to write to achieve my code:</p> <pre><code>float ComputeShadowFactor(samplerCubeShadow ShadowCubeMap, vec3 VertToLightWS) { float ShadowVec = texture(ShadowCubeMap, vec4(VertToLightWS, 1.0)); ShadowVec = DepthValueToDistance(ShadowVec); if (ShadowVec * ShadowVec &gt; dot(VertToLightWS, VertToLightWS)) return 1.0; return 0.0; } </code></pre> <p>The DepthValueToDistance function being my actual problem.</p>
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    1. CO"Is there a solution to my problem?" Convert distance to depth, compare with stored depth in cubemap. "unappliable for cube map shadows" I think 5..7 years ago somebody called "ron frazier" wrote an article about using cubemaps for shadow mapping.
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    2. CO@SigTerm http://www.ronfrazier.net/apparition/index.html?appmain=research/index.html is what I think you are talking about.
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    3. CO@JohnRiselvato: Yep. I **think** it was [this](http://www.ronfrazier.net/apparition/index.html?appmain=research/index.html) article. It is obviously possible to do something similar with modern OpenGL/better precision (there are floating point textures, GLSL, `*shadow` samplers, etc) - I just don't have a working snippet nearby and don't feel like writing one.
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