• Advertisement
Sign in to follow this  

OpenGL OpenGL Tessellation

This topic is 1652 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

I'm having a hard time getting OpenGL Tessellation to work. I have been struggling with it for about a month now. I've looked at a lot of example code and what I am doing doesn't seem that different to what they are doing in their code. I was wondering if anyone could be a second pair of eyes and maybe point out why it isn't working.

My scene is only rendering a black screen.

My shaders are as follows:

 

Vertex Shader

#version 400
#extension GL_ARB_tessellation_shader: enable
#extension GL_ARB_separate_shader_objects: enable

layout(location = 0) in vec3 vertexPosition;

void main()
{
    gl_Position = vec4(vertexPosition, 1.0);
}

Tessellation Control Shader

#version 400
#extension GL_ARB_separate_shader_objects: enable

layout(vertices = 3) out;

void main()
{
    float inLevel = 2;
    float outLevel = 2;
    
    gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
    
    if (gl_InvocationID == 0)
    {
        gl_TessLevelOuter[0] = outLevel;
        gl_TessLevelOuter[1] = outLevel;
        gl_TessLevelOuter[2] = outLevel;
        gl_TessLevelOuter[3] = outLevel;

        gl_TessLevelInner[0] = inLevel;
        gl_TessLevelInner[1] = inLevel;
    }
}

Tessellation Eval Shader

#version 400
#extension GL_ARB_tessellation_shader: enable
#extension GL_ARB_separate_shader_objects: enable

layout(triangles, equal_spacing, ccw) in;

uniform mat4 uMVPMatrix;

void main()
{
    vec4 p0 = gl_TessCoord.x * gl_in[0].gl_Position;
    vec4 p1 = gl_TessCoord.y * gl_in[1].gl_Position;
    vec4 p2 = gl_TessCoord.z * gl_in[2].gl_Position;

    vec4 newCoord = normalize(p0 + p1 + p2);
    gl_Position = newCoord;
}

Geometry Shader

#version 400
#extension GL_ARB_separate_shader_objects: enable

layout(triangles) in;
layout(triangle_strip, max_vertices = 3) out;

uniform mat4 uMVPMatrix;

uniform bool UseWaveGeometry;
uniform float GameTime;

layout(location = 3) out vec4 vColor;

float rand(vec2 n)
{
    return 0.5 + 0.5 * fract(sin(dot(n.xy, vec2(12.9898, 78.233)))* 43758.5453);
}

void setUpValues(int index)
{
    vec4 vertPosit = gl_in[index].gl_Position;
    
    if(UseWaveGeometry)
    {
        vertPosit.y = vertPosit.y + (GameTime + ((cos(vertPosit.x)) * GameTime) - ((sin(vertPosit.x))*GameTime)*2.2);
    }
    
    float cval = int(vertPosit.x) % 2 + int(vertPosit.y)%2;
    vColor = vec4(cval, cval, cval, 1.0);

    gl_Position = uMVPMatrix * vertPosit;
}

void main()
{
    for(int i = 0; i < 3; i++)
    {
        setUpValues(i);
        EmitVertex();
    }
    EndPrimitive();
}

Fragment Shader

#version 400
#extension GL_EXT_gpu_shader4: enable
#extension GL_ARB_separate_shader_objects: enable

uniform float ColorAlpha;

layout(location = 3) in vec4 vColor;

layout(location = 0) out vec4 FragColor;

void main()
{
    vec4 color = vec4(vColor.r, vColor.g, vColor.b, ColorAlpha);
    
    FragColor = color;
}

Thank you for your time,
Marty

Edited by martyj2009

Share this post


Link to post
Share on other sites
Advertisement
First of all I assume that rendering single triangle with only VS and FS works (e.g. you don't have issues in calling glDrawArrays/glDrawElements).
 
Some points that probably cause issues:
1.) Names with out qualifier in some shader should correspond to names with in qualifier in the shader describing next stage. At least unless you use layout qualifier and separate shader objects extensions... e.g.:
// Standard way of passing "varyings" from one shader to another. The GLSL compliler does pattern
// matching between their names and connects them.
[Vertex Shader]
out vec3 vsVertexPosition;
out vec3 vsVertexNormal;

[Geometry Shader]
in vec3 vsVertexPosition[];
in vec3 vsVertexNormal[];

// Another possible way since ARB_separate_shader_objects - available since OpenGL 4.1, core
// since OpenGL 4.3 - this one explicitly says which "varyings" links together. Note that
// using this approach the corresponding ones can have different names! Otherwise they can't
[Vertex Shader]
layout(location = 0) out vec3 position;
layout(location = 1) out vec3 normal;

[Geometry Shader]
layout(location = 0) in vec3 pos;
layout(location = 1) in vec3 n;

// But this is NOT possible, the GLSL compiler can't tell which variables can be connected
// together.
[Vertex Shader]
out vec3 pos;
out vec3 normal;

[Geometry Shader]
in vec3 mPosition;
in vec3 mNormal;
2.) Version definition should be same in all shaders! On AMD this can result in error and compilation will fail, thus the shaders won't run.

3.) Don't mix gl_in/gl_out and in/out. This is bad and results in (very) messy shaders.

4.) Tessellation shaders should have
#extension GL_ARB_tessellation_shader : enable
These are just few points by quickly going through your code. I can post you shader code of very basic tessellation example that works - if you can't make it work. It's really very basic example that needs just 2 parameters - view and projection matrices. Edited by Vilem Otte

Share this post


Link to post
Share on other sites

Thank you for the reply. Sorry for the late response. I read your message a few days ago.

 

The reason I didn't use the layout location identifiers is that I am dynamically getting the location in my C code by the name of the attribute. I also keep my variables named the same. Although it would make for easier to understand shader code if I used them as well. That way users can see at a glance what output matches up with what input.

 

I will implemented this and post my results.

 

Thank you very much for the feedback. It is greatly appreciated.

 

Edit

--------------------------------------------

 

I modified my previous post with the updated shaders. I still get the same issues with tessellation.

Edited by martyj2009

Share this post


Link to post
Share on other sites

Anyone have any idea? Anything at all I could try? Any feedback would be greatly appreciated.

 

 

Edit:

---------------------------

I simplefied the code. I still get a black screen when the tessellation shaders are enabled. It renders a scene with them commented out.

Edited by martyj2009

Share this post


Link to post
Share on other sites

I ran all the shaders through AMD's GPU shaderAnalyzer and shaders 2,3, and 5 all have reported errors.  Most notable, 2 is using variables that were not declared.

 

Also, there is usually a huge problem with shader tech that is very new.  A lot of it is not tested against multiple GPU's and it can take a while for the GPU manufacturers to play catch-up with one another. Often you will run into compatibility issues if you have a different brand than what the code was tested on.  

 

Here's another site that you can cross-reference against.  

 

http://prideout.net/blog/?p=48

 

ShaderAnalyzer only has a problem with the tess eval shader in this example. 

Share this post


Link to post
Share on other sites

I have been using that reference as a tessellation example. 

 

The biggest problem is that my code base is so huge. I have texture arrays for height maps, FBO for shaows, reflections, and a bunch of other stuff which complicate code slightly.

 

I will check out the AMD GPU shader analyzer. Thanks for the info. I will post an update when I test it

Edited by martyj2009

Share this post


Link to post
Share on other sites

I finally figured out my issue.

 

It wasn't shaders at all. My problem with tessellation was that I was drawing my objects using GL_TRIANGLES. Tessellation only works on GL_PATCHES.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Now

  • Advertisement
  • Similar Content

    • By khawk
      We've just released all of the source code for the NeHe OpenGL lessons on our Github page at https://github.com/gamedev-net/nehe-opengl. code - 43 total platforms, configurations, and languages are included.
      Now operated by GameDev.net, NeHe is located at http://nehe.gamedev.net where it has been a valuable resource for developers wanting to learn OpenGL and graphics programming.

      View full story
    • By TheChubu
      The Khronos™ Group, an open consortium of leading hardware and software companies, announces from the SIGGRAPH 2017 Conference the immediate public availability of the OpenGL® 4.6 specification. OpenGL 4.6 integrates the functionality of numerous ARB and EXT extensions created by Khronos members AMD, Intel, and NVIDIA into core, including the capability to ingest SPIR-V™ shaders.
      SPIR-V is a Khronos-defined standard intermediate language for parallel compute and graphics, which enables content creators to simplify their shader authoring and management pipelines while providing significant source shading language flexibility. OpenGL 4.6 adds support for ingesting SPIR-V shaders to the core specification, guaranteeing that SPIR-V shaders will be widely supported by OpenGL implementations.
      OpenGL 4.6 adds the functionality of these ARB extensions to OpenGL’s core specification:
      GL_ARB_gl_spirv and GL_ARB_spirv_extensions to standardize SPIR-V support for OpenGL GL_ARB_indirect_parameters and GL_ARB_shader_draw_parameters for reducing the CPU overhead associated with rendering batches of geometry GL_ARB_pipeline_statistics_query and GL_ARB_transform_feedback_overflow_querystandardize OpenGL support for features available in Direct3D GL_ARB_texture_filter_anisotropic (based on GL_EXT_texture_filter_anisotropic) brings previously IP encumbered functionality into OpenGL to improve the visual quality of textured scenes GL_ARB_polygon_offset_clamp (based on GL_EXT_polygon_offset_clamp) suppresses a common visual artifact known as a “light leak” associated with rendering shadows GL_ARB_shader_atomic_counter_ops and GL_ARB_shader_group_vote add shader intrinsics supported by all desktop vendors to improve functionality and performance GL_KHR_no_error reduces driver overhead by allowing the application to indicate that it expects error-free operation so errors need not be generated In addition to the above features being added to OpenGL 4.6, the following are being released as extensions:
      GL_KHR_parallel_shader_compile allows applications to launch multiple shader compile threads to improve shader compile throughput WGL_ARB_create_context_no_error and GXL_ARB_create_context_no_error allow no error contexts to be created with WGL or GLX that support the GL_KHR_no_error extension “I’m proud to announce OpenGL 4.6 as the most feature-rich version of OpenGL yet. We've brought together the most popular, widely-supported extensions into a new core specification to give OpenGL developers and end users an improved baseline feature set. This includes resolving previous intellectual property roadblocks to bringing anisotropic texture filtering and polygon offset clamping into the core specification to enable widespread implementation and usage,” said Piers Daniell, chair of the OpenGL Working Group at Khronos. “The OpenGL working group will continue to respond to market needs and work with GPU vendors to ensure OpenGL remains a viable and evolving graphics API for all its customers and users across many vital industries.“
      The OpenGL 4.6 specification can be found at https://khronos.org/registry/OpenGL/index_gl.php. The GLSL to SPIR-V compiler glslang has been updated with GLSL 4.60 support, and can be found at https://github.com/KhronosGroup/glslang.
      Sophisticated graphics applications will also benefit from a set of newly released extensions for both OpenGL and OpenGL ES to enable interoperability with Vulkan and Direct3D. These extensions are named:
      GL_EXT_memory_object GL_EXT_memory_object_fd GL_EXT_memory_object_win32 GL_EXT_semaphore GL_EXT_semaphore_fd GL_EXT_semaphore_win32 GL_EXT_win32_keyed_mutex They can be found at: https://khronos.org/registry/OpenGL/index_gl.php
      Industry Support for OpenGL 4.6
      “With OpenGL 4.6 our customers have an improved set of core features available on our full range of OpenGL 4.x capable GPUs. These features provide improved rendering quality, performance and functionality. As the graphics industry’s most popular API, we fully support OpenGL and will continue to work closely with the Khronos Group on the development of new OpenGL specifications and extensions for our customers. NVIDIA has released beta OpenGL 4.6 drivers today at https://developer.nvidia.com/opengl-driver so developers can use these new features right away,” said Bob Pette, vice president, Professional Graphics at NVIDIA.
      "OpenGL 4.6 will be the first OpenGL release where conformant open source implementations based on the Mesa project will be deliverable in a reasonable timeframe after release. The open sourcing of the OpenGL conformance test suite and ongoing work between Khronos and X.org will also allow for non-vendor led open source implementations to achieve conformance in the near future," said David Airlie, senior principal engineer at Red Hat, and developer on Mesa/X.org projects.

      View full story
    • By _OskaR
      Hi,
      I have an OpenGL application but without possibility to wite own shaders.
      I need to perform small VS modification - is possible to do it in an alternative way? Do we have apps or driver modifictions which will catch the shader sent to GPU and override it?
    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glUseProgram(program.get());
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glUseProgram(0);
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
      glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
       
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
    • By Jonathan2006
      My question: is it possible to transform multiple angular velocities so that they can be reinserted as one? My research is below:
      // This works quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); quat quaternion2 = GEMultiplyQuaternions(quaternion1, GEQuaternionFromAngleRadians(angleRadiansVector2)); quat quaternion3 = GEMultiplyQuaternions(quaternion2, GEQuaternionFromAngleRadians(angleRadiansVector3)); glMultMatrixf(GEMat4FromQuaternion(quaternion3).array); // The first two work fine but not the third. Why? quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); vec3 vector1 = GETransformQuaternionAndVector(quaternion1, angularVelocity1); quat quaternion2 = GEQuaternionFromAngleRadians(angleRadiansVector2); vec3 vector2 = GETransformQuaternionAndVector(quaternion2, angularVelocity2); // This doesn't work //quat quaternion3 = GEQuaternionFromAngleRadians(angleRadiansVector3); //vec3 vector3 = GETransformQuaternionAndVector(quaternion3, angularVelocity3); vec3 angleVelocity = GEAddVectors(vector1, vector2); // Does not work: vec3 angleVelocity = GEAddVectors(vector1, GEAddVectors(vector2, vector3)); static vec3 angleRadiansVector; vec3 angularAcceleration = GESetVector(0.0, 0.0, 0.0); // Sending it through one angular velocity later in my motion engine angleVelocity = GEAddVectors(angleVelocity, GEMultiplyVectorAndScalar(angularAcceleration, timeStep)); angleRadiansVector = GEAddVectors(angleRadiansVector, GEMultiplyVectorAndScalar(angleVelocity, timeStep)); glMultMatrixf(GEMat4FromEulerAngle(angleRadiansVector).array); Also how do I combine multiple angularAcceleration variables? Is there an easier way to transform the angular values?
  • Advertisement