Sign in to follow this  
BenS1

OpenGL Rendering Normals (For Debugging) using the Geometry Shader

Recommended Posts

BenS1    352
Hi,

I've got an annoying lighting problem with my terrain engine and I'm not sure if the problem is with my calculation of the terrain surface normals or something else.

I've tried single stepping through the HLSL code but personally I find it a little difficult to visualize vectors when they are just presented as numbers, so I'd much rather actually see the vectors (Normals in this case).

I guess it should be quite trivial to create a Geometry shader that renders the normals... but rather than reinvent the wheel I thought I'd just check to see if anyone has such a shader that I could use? (HLSL SM 5 compatible)

I've tried a quick search but all I've found are OpenGL versions and no HLSL versions.

Anyway, if anyone has such a shader then great. If not then I'll write my own and share it on here for anyone else that may want to use it in future.

Thanks
Ben

Share this post


Link to post
Share on other sites
Tordin    625
have you tired render the value as a color? it´s more easy to think of when you got colors. Or atleast i belive so. Edited by Tordin

Share this post


Link to post
Share on other sites
Nik02    4348
I haven't seen a ready-made one, but the logic is indeed trivial. You just output a line (of uniform length) that starts from the vertex position and points to the direction of the normal.

While at it, you can also draw tangent and bitangent lines as well in the same shader. If you do, be sure to output meaningful colors to go with the lines.

If you want to visualize the face normals instead of vertex normals, just average the vertex normals for the current triangle (and take the centroid or average of the positions to find the "center" of the triangle) and normalize the result before streaming it out from the GS.

Tordin's suggestion is also good. Red would represent the range of -1...+1 in the x direction, green in the y... and you get the idea. Edited by Nik02

Share this post


Link to post
Share on other sites
BenS1    352
Thanks both,

Yes I'll try the colour idea first, although it'll still be a little difficult to visualize that a triangle of a certain colour represents a normal is a certain direction, but it could still be very useful.

I'll go on to implementing the geometry shader version second and I'll post the code on here for anyone that wants it.

Thanks
Ben

Share this post


Link to post
Share on other sites
BenS1    352
Interesting... it took less than 30 seconds to implement the rendering of normals as a colour idea and it indeed shows that there's something "not normal with my normals!" :)

I must have a problem with my Sobel filter somewhere

Off to the debugger...

Share this post


Link to post
Share on other sites
BenS1    352
Sure Nik02, I agree its great for some stuff, but it wouldn't be obvious for example if all my Normals were pointing in the opposite direction.

As it happens, in this case the colours did show quite clearly that something was not right, so I removed my Sobel filter based Normal calculator and replaced it with a simple Normal calculator (i.e. takes 3 points on the terrain, creates 2 vectors and then the Cross of those 2 vectors). All works perfectly now.

At some point I'll revisit the Sobel filter, but for thsi project I don't think I need it anyway.

Big thanks to your help... this lighting problem had been driving me crazy for days.

Thanks
Ben

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 pseudomarvin
      I assumed that if a shader is computationally expensive then the execution is just slower. But running the following GLSL FS instead just crashes
      void main() { float x = 0; float y = 0; int sum = 0; for (float x = 0; x < 10; x += 0.00005) { for (float y = 0; y < 10; y += 0.00005) { sum++; } } fragColor = vec4(1, 1, 1 , 1.0); } with unhandled exception in nvoglv32.dll. Are there any hard limits on the number of steps/time that a shader can take before it is shut down? I was thinking about implementing some time intensive computation in shaders where it would take on the order of seconds to compute a frame, is that possible? Thanks.
    • By Arulbabu Donbosco
      There are studios selling applications which is just copying any 3Dgraphic content and regenerating into another new window. especially for CAVE Virtual reality experience. so that the user opens REvite or CAD or any other 3D applications and opens a model. then when the user selects the rendered window the VR application copies the 3D model information from the OpenGL window. 
      I got the clue that the VR application replaces the windows opengl32.dll file. how this is possible ... how can we copy the 3d content from the current OpenGL window.
      anyone, please help me .. how to go further... to create an application like VR CAVE. 
       
      Thanks
    • By cebugdev
      hi all,

      i am trying to build an OpenGL 2D GUI system, (yeah yeah, i know i should not be re inventing the wheel, but this is for educational and some other purpose only),
      i have built GUI system before using 2D systems such as that of HTML/JS canvas, but in 2D system, i can directly match a mouse coordinates to the actual graphic coordinates with additional computation for screen size/ratio/scale ofcourse.
      now i want to port it to OpenGL, i know that to render a 2D object in OpenGL we specify coordiantes in Clip space or use the orthographic projection, now heres what i need help about.
      1. what is the right way of rendering the GUI? is it thru drawing in clip space or switching to ortho projection?
      2. from screen coordinates (top left is 0,0 nd bottom right is width height), how can i map the mouse coordinates to OpenGL 2D so that mouse events such as button click works? In consideration ofcourse to the current screen/size dimension.
      3. when let say if the screen size/dimension is different, how to handle this? in my previous javascript 2D engine using canvas, i just have my working coordinates and then just perform the bitblk or copying my working canvas to screen canvas and scale the mouse coordinates from there, in OpenGL how to work on a multiple screen sizes (more like an OpenGL ES question).
      lastly, if you guys know any books, resources, links or tutorials that handle or discuss this, i found one with marekknows opengl game engine website but its not free,
      Just let me know. Did not have any luck finding resource in google for writing our own OpenGL GUI framework.
      IF there are no any available online, just let me know, what things do i need to look into for OpenGL and i will study them one by one to make it work.
      thank you, and looking forward to positive replies.
    • By fllwr0491
      I have a few beginner questions about tesselation that I really have no clue.
      The opengl wiki doesn't seem to talk anything about the details.
       
      What is the relationship between TCS layout out and TES layout in?
      How does the tesselator know how control points are organized?
          e.g. If TES input requests triangles, but TCS can output N vertices.
             What happens in this case?
      In this article,
      http://www.informit.com/articles/article.aspx?p=2120983
      the isoline example TCS out=4, but TES in=isoline.
      And gl_TessCoord is only a single one.
      So which ones are the control points?
      How are tesselator building primitives?
    • By Orella
      I've been developing a 2D Engine using SFML + ImGui.
      Here you can see an image
      The editor is rendered using ImGui and the scene window is a sf::RenderTexture where I draw the GameObjects and then is converted to ImGui::Image to render it in the editor.
      Now I need to create a 3D Engine during this year in my Bachelor Degree but using SDL2 + ImGui and I want to recreate what I did with the 2D Engine. 
      I've managed to render the editor like I did in the 2D Engine using this example that comes with ImGui. 
      3D Editor preview
      But I don't know how to create an equivalent of sf::RenderTexture in SDL2, so I can draw the 3D scene there and convert it to ImGui::Image to show it in the editor.
      If you can provide code will be better. And if you want me to provide any specific code tell me.
      Thanks!
  • Popular Now