• Advertisement
Sign in to follow this  

OpenGL [D3D] Showing wireframe over shaded geometry

This topic is 3869 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

Hi All, To get good results, in OpenGL exists a function to offset the wireframe 'just a little bit' closer than the filled polygons. Can this be done with Direct3D? Thanks so much guys. Alberto

Share this post


Link to post
Share on other sites
Advertisement
When you say a just a little bit closer, you mean that it makes the wireframe draw above the filled polygons so that you see both the solid mesh and it's edges?
If so, then the problem is that since they both are at the same distance from the camera, Direct3D will not know who should be drawn (its called z-fighting or flimmering). There are many ways of solving this. One is to disable the Z-Buffer or disabling the Z-Writing temporarily and then Direct3D won't confuse between the depths. Another technique is to use the Z-Bias but I have suspicions about that one, it didn't seem to work last time I tried. You can also use stenciling to solve this but it's a bit more complicated; search for how to use 'decals' if you want to use this method.
Hope this helped,
Uri

Share this post


Link to post
Share on other sites
Decals?!?

I knew about the stencil approach but not about Z-bias.

I will try to fid something with google...

Thanks,

Alberto

Share this post


Link to post
Share on other sites
I think the "function to offset the wireframe 'just a little bit' closer than the filled polygons" is just Z-bias :)

You can do it in Direct3D by doing this :

float zBias = 0.01f; // your 'offset' value. Play with it until you get good results
pD3DDevice->SetRenderState(D3DRS_DEPTHBIAS, *(DWORD *)&zBias);

Share this post


Link to post
Share on other sites
Thanks a lot paic,


So I:

1) Set the zBias = 0.0f;
2) Draw shaded triangles
3) Set the zBias = 0.01f;
4) Draw wireframe triangles

Ok?

Alberto

Share this post


Link to post
Share on other sites
Thanks a lot Jack,


Looks like zBias doesn't work for lines... What if I need to outline a mesh of 4x4 = 16x2 = 32 triangle with 4+4+4+4 lines?!?


Alberto

Share this post


Link to post
Share on other sites
Another technique is to modify your projection matrix to push the near plane out a little which essentially brings all generated depth values back a bit. This would only be worth doing if you can batch your stuff such that all solid stuff is drawn and then modify proj matrix then render all wire stuff. It seems to work relatively well in practise.

Share this post


Link to post
Share on other sites
Quote:
Original post by devdept
Thanks a lot Jack,


Looks like zBias doesn't work for lines... What if I need to outline a mesh of 4x4 = 16x2 = 32 triangle with 4+4+4+4 lines?!?


Alberto

Couldn't you apply the depth bias to the solid object and leave the lines at the original depth?

Share this post


Link to post
Share on other sites
Hi devdept,

Re: Looks like zBias doesn't work for lines...

Are you sure?

I just happen to be looking to solving this problem at the same time as you
(coming from a long history of opengl to Directx) and found a solution;

I too came to the same conclusion that paic's suggestion:

"You can do it in Direct3D by doing this :

float zBias = 0.01f; // your 'offset' value. Play with it until you get good results
pD3DDevice->SetRenderState(D3DRS_DEPTHBIAS, *(DWORD *)&zBias);"

does not work because

1) directx docs mention it does not work with lines
2) I tried it anyway..and it didn't work.

But:

See if the following helps:

1) take a look at Ati sample at
http://ati.amd.com/developer/samples/dx9/DepthBias.html

It contains code to check whether device can do antialiased lines as well
as the effect you are looking for I think.


2)I have found though that the value of zBias is critcal. Perhaps along with
the slope scale. You need to experiment I guess.

When I say lines: I am talking about drawing as mesh in wireframe mode. Not sure if thats what you also mean.

I was able to get this working on an old geforce 4, so I am assuming
most systems should support it today (including yours).

3) In my app the z bias is modified depending on the scale of the world.
contrived e.g.-> say if the distance between 2 pixels on the screen is 1 3d world unit the
zbias would be about 0.005f, if the distance between 2 pixels on the screen
gets to 10,000 units zbias is down around 0.00001f ! (such small numbers!)

Anyhow, you may like to look at the ati sample and revisit the
D3DRS_DEPTHBIAS idea again. It worked for me (almost as easliy as the opengl
equivalent?...now that it works!).









Share this post


Link to post
Share on other sites
If your card supports it I'd recommend slope scaled bias, it gives much better results on oblique polygons.

Share this post


Link to post
Share on other sites
Yes, maybe moving away the solid is easier, so you don't need to apply zBias to lines.

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