Sign in to follow this  
KaiserJohan

OpenGL Shadowsampler comparison

Recommended Posts

KaiserJohan    2317

Doing cascaded shadow mapping, and I need some confirmation I am doing the right thing. The shadow mapping works (mostly) but on a few angles the shadows vanish.

 

The sampler is setup like this:

 

GLCALL(glGenSamplers(1, &mTextureSampler));
GLCALL(glSamplerParameteri(mTextureSampler, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE));
GLCALL(glSamplerParameteri(mTextureSampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR));
GLCALL(glSamplerParameteri(mTextureSampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR));
GLCALL(glSamplerParameteri(mTextureSampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE));
GLCALL(glSamplerParameteri(mTextureSampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE));
GLCALL(glSamplerParameteri(mTextureSampler, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE));
GLCALL(glBindSampler(OpenGLTexture::TEXTURE_UNIT_SHADOW_DIRECTIONAL, mTextureSampler));

I do depth comparison rather than distance comparison; my depth textures thus contain depth values.

 

vec4 projCoords = UnifDirLightPass.mVPMatrix[index] * vec4(worldPos, 1.0);                                                  
projCoords.w    = projCoords.z - DEPTH_BIAS;                                                                                
projCoords.z    = float(index);                                                                                             
float visibilty = texture(unifShadowTexture, projCoords);                                                                   


float angleNormal = clamp(dot(normal, UnifDirLightPass.mLightDir.xyz), 0, 1);                                               


fragColor = vec4(diffuse, 1.0) * visibilty * angleNormal * UnifDirLightPass.mLightColor;                                    

"unifShadowTexture" is of type "sampler2DarrayShadow", and "UnifDirLightPass.mVPMatrix[]" contains the bias * lightProj * lightView matrix for each split.

 

 

1. By having MIN/MAG filtering to GL_LINEAR, shouldn't I also have visibility = 0.5 for some samples? All I see is either 0.0 or 1.0.

 

2. Is the comparison in texture() valid? I believe I read somewhere that depth values aren't stored linearly, does this create a problem when I try to compare it against bias * lightProj * lightView * worldPosition?

 

3. For what reason would you use distance comparison (= writing the squared distance to the depth texture) over depth comparison for shadow mapping? It just seems like extra computations?

 

4. I am using shadow samplers, which gives me 0.0 or 1.0 values. How can I accomplish soft shadows with this for directional and point lights with such binary values to work with?

 

5. Why would you not use shadow samplers over normal samplers in shadow mapping?

 

Thanks

Edited by KaiserJohan

Share this post


Link to post
Share on other sites
Ashaman73    13715

1. By having MIN/MAG filtering to GL_LINEAR, shouldn't I also have visibility = 0.5 for some samples? All I see is either 0.0 or 1.0.

The result of the texture sampler (you have a shadow sampler which do a depth comparision) is either in shadow or not in shadow (use PCF or other fitlerings to get soft shadows). The linear filtering is used to get the right depth comparision value, but the final result is only the binary result of the comparision of the filtered depth value and your reference value.

 

 

 


4. I am using shadow samplers, which gives me 0.0 or 1.0 values. How can I accomplish soft shadows with this for directional and point lights with such binary values to work with?

To create soft  shadows , you can't use standard texture filtering methods (eg linear filtering), they will not really work. An often used approach is, to sample multiple shadow samples and calculate the shadow values yourself (eg PCF), I use ie 12-24 samples per rendered pixel to soften my shadows in my engine. Look out for hardware supported filtering too (again PCF).

 

 

5. Why would you not use shadow samplers over normal samplers in shadow mapping?

Because the hardware might be optimize to do the comparision of the shadow values, and the hardware could support already some degree of PCF to soften your shadows. In comes all down to better out-of-the-box hardware support.

Edited by Ashaman73

Share this post


Link to post
Share on other sites
Hodgman    51222

1. By having MIN/MAG filtering to GL_LINEAR, shouldn't I also have visibility = 0.5 for some samples? All I see is either 0.0 or 1.0.

The result of the texture sampler (you have a shadow sampler which do a depth comparision) is either in shadow or not in shadow (use PCF or other fitlerings to get soft shadows). The linear filtering is used to get the right depth comparision value, but the final result is only the binary result of the comparision of the filtered depth value and your reference value.

I'm not sure about in GL, but this is actually how you enable hardware-accelerated PCF in D3D. The comparison happens first, on 4 unfiltered depth values, and then those 0/1 comparison results are linearly filtered.

Share this post


Link to post
Share on other sites
KaiserJohan    2317

Is there no way to increase the samples used for hardware-accelerated PCF? It still looks very blocky with GL_LINEAR for OpenGL. Doing 12 samples software-style, does that mean 12 texture lookups? sounds expensive?

Share this post


Link to post
Share on other sites
Ashaman73    13715

Doing 12 samples software-style, does that mean 12 texture lookups?

You can use branching to your benefit. First make a quick test with 4 lookups, if all are either inside or outside of the shadow, you can mark the pixel as shadowed/unshadowed. If you got a mixed result, just look up X more shadow texels. The benefit comes from how GPUs work (atleast some, depends on hardware). GPU often group the processing units into wavefronts, cells whatever, which process multiple input data as single process (they do the same work at the same time). This is a reason, that branching hurts sometimes, because if some units of this group needs to do something else, the rest of the group need to wait and the total amount of processing time of the whole group increases.

 

Nevertheless, in our case, we want to optimize from, lets say 20 texel to just 4 texel access (sometimes). That is, if just one unit of a wavefront hits a mixed shadowed result, all pixels need the same (worst case) time. But if all unit just need 4 texel accesses, you suddently save a lot of processing time for this wavefront. A pixel wavefront eg has a 8x8 block size, thought this really depends on the hardware architecture. And the probabilty, that a 8x8 block is completly inside or outside the shadow , is quite high. Instead of lets say 20 texel access for the worst case scenario, you suddenly have an average case of ~12 texel access (assumption 50% hit rate => 4 + 16*50%).

 

The benefit:

If you work on a console, you should have access to detailed GPU archtecture information and can utilize it accordingly. If you work on the PC with unknown hardware, just build in an option which let you choose your shadow smoothness (from 1 sample up to 48 samples) and the user is able to decide himself which is best (performance vs quality).

Edited by Ashaman73

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Similar Content

    • By Kjell Andersson
      I'm trying to get some legacy OpenGL code to run with a shader pipeline,
      The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
      I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
      I've got a version 330 vertex shader to somewhat work:
      #version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
      What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
      Question:
      What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?
       
      Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.
    • By markshaw001
      Hi i am new to this forum  i wanted to ask for help from all of you i want to generate real time terrain using a 32 bit heightmap i am good at c++ and have started learning Opengl as i am very interested in making landscapes in opengl i have looked around the internet for help about this topic but i am not getting the hang of the concepts and what they are doing can some here suggests me some good resources for making terrain engine please for example like tutorials,books etc so that i can understand the whole concept of terrain generation.
       
    • By KarimIO
      Hey guys. I'm trying to get my application to work on my Nvidia GTX 970 desktop. It currently works on my Intel HD 3000 laptop, but on the desktop, every bind textures specifically from framebuffers, I get half a second of lag. This is done 4 times as I have three RGBA textures and one depth 32F buffer. I tried to use debugging software for the first time - RenderDoc only shows SwapBuffers() and no OGL calls, while Nvidia Nsight crashes upon execution, so neither are helpful. Without binding it runs regularly. This does not happen with non-framebuffer binds.
      GLFramebuffer::GLFramebuffer(FramebufferCreateInfo createInfo) { glGenFramebuffers(1, &fbo); glBindFramebuffer(GL_FRAMEBUFFER, fbo); textures = new GLuint[createInfo.numColorTargets]; glGenTextures(createInfo.numColorTargets, textures); GLenum *DrawBuffers = new GLenum[createInfo.numColorTargets]; for (uint32_t i = 0; i < createInfo.numColorTargets; i++) { glBindTexture(GL_TEXTURE_2D, textures[i]); GLint internalFormat; GLenum format; TranslateFormats(createInfo.colorFormats[i], format, internalFormat); // returns GL_RGBA and GL_RGBA glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, createInfo.width, createInfo.height, 0, format, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); DrawBuffers[i] = GL_COLOR_ATTACHMENT0 + i; glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, textures[i], 0); } if (createInfo.depthFormat != FORMAT_DEPTH_NONE) { GLenum depthFormat; switch (createInfo.depthFormat) { case FORMAT_DEPTH_16: depthFormat = GL_DEPTH_COMPONENT16; break; case FORMAT_DEPTH_24: depthFormat = GL_DEPTH_COMPONENT24; break; case FORMAT_DEPTH_32: depthFormat = GL_DEPTH_COMPONENT32; break; case FORMAT_DEPTH_24_STENCIL_8: depthFormat = GL_DEPTH24_STENCIL8; break; case FORMAT_DEPTH_32_STENCIL_8: depthFormat = GL_DEPTH32F_STENCIL8; break; } glGenTextures(1, &depthrenderbuffer); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); glTexImage2D(GL_TEXTURE_2D, 0, depthFormat, createInfo.width, createInfo.height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depthrenderbuffer, 0); } if (createInfo.numColorTargets > 0) glDrawBuffers(createInfo.numColorTargets, DrawBuffers); else glDrawBuffer(GL_NONE); if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) std::cout << "Framebuffer Incomplete\n"; glBindFramebuffer(GL_FRAMEBUFFER, 0); width = createInfo.width; height = createInfo.height; } // ... // FBO Creation FramebufferCreateInfo gbufferCI; gbufferCI.colorFormats = gbufferCFs.data(); gbufferCI.depthFormat = FORMAT_DEPTH_32; gbufferCI.numColorTargets = gbufferCFs.size(); gbufferCI.width = engine.settings.resolutionX; gbufferCI.height = engine.settings.resolutionY; gbufferCI.renderPass = nullptr; gbuffer = graphicsWrapper->CreateFramebuffer(gbufferCI); // Bind glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo); // Draw here... // Bind to textures glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textures[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, textures[1]); glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, textures[2]); glActiveTexture(GL_TEXTURE3); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); Here is an extract of my code. I can't think of anything else to include. I've really been butting my head into a wall trying to think of a reason but I can think of none and all my research yields nothing. Thanks in advance!
    • By Adrianensis
      Hi everyone, I've shared my 2D Game Engine source code. It's the result of 4 years working on it (and I still continue improving features ) and I want to share with the community. You can see some videos on youtube and some demo gifs on my twitter account.
      This Engine has been developed as End-of-Degree Project and it is coded in Javascript, WebGL and GLSL. The engine is written from scratch.
      This is not a professional engine but it's for learning purposes, so anyone can review the code an learn basis about graphics, physics or game engine architecture. Source code on this GitHub repository.
      I'm available for a good conversation about Game Engine / Graphics Programming
    • By C0dR
      I would like to introduce the first version of my physically based camera rendering library, written in C++, called PhysiCam.
      Physicam is an open source OpenGL C++ library, which provides physically based camera rendering and parameters. It is based on OpenGL and designed to be used as either static library or dynamic library and can be integrated in existing applications.
       
      The following features are implemented:
      Physically based sensor and focal length calculation Autoexposure Manual exposure Lense distortion Bloom (influenced by ISO, Shutter Speed, Sensor type etc.) Bokeh (influenced by Aperture, Sensor type and focal length) Tonemapping  
      You can find the repository at https://github.com/0x2A/physicam
       
      I would be happy about feedback, suggestions or contributions.

  • Popular Now