• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
thomasfn1

OpenGL
Material blending in a deferred renderer

6 posts in this topic

So I'm about to start writing a scene manager and renderer for a game and I'm going to be using deferred shading. My scenes are going to be populated by lots of objects so I'll be using instancing to cut down on draw calls. I also want to try and defer material and texture sampling by having my objects output a material ID into a single-channel FB. Some kind of mega-shader would then convert the material ID into a diffuse and normal sample (probably by having a texture store all material attributes and using the material ID as a v coordinate, and by using texture arrays to get access to different textures).

 

This raises an issue with material blending. My scene will also feature a terrain at all times (other than when the player is looking up) and I want the textures on my terrain to blend from one to another across a tile. Of course, since the mapping between a pixel and material ID is 1-1, there's no way to represent blending between multiple materials using the setup described above. The way I see it, I have 2 options:

 

  1. Instead of using a single material ID per pixel, use multiple material IDs and have a second output which would be the weights of the materials to blend with in the mega-shader.
  2. Draw the terrain seperately straight into the GBuffer after the mega-shader has been run on the scene, using the depth-buffer from the material ID FB. Texture sampling would occur normally here. Lights would have to be rendered in a seperate pass from the mega-shader.

Both options have pros and cons. With option 1, the advantages of drawing into a relatively small FB are lost (now we have 2 textures to render into with weights) and you can only fit up to 4 materials to blend at once (though this might be enough for terrain blending?). Additionally, the uber-shader now has to make up to 4 samples into the material texture and corresponding diffuse/normal textures and blend everything together, potentially taking 4x as long to draw. I'm not sure if it's possible to optimise this somehow such that only 1 sample is made if only 1 material is used with full weight.

 

With option 2, the uber-shader remains relatively light-weight but there's an extra pass involved and there's probably some caveat of drawing everything in a strange order. Also benefits of the deferred rendering in this case are lost for the terrain (which will have a very large surface area and is also likely to be occluded by many polygons (trees, grass etc) and so would probably benefit from deferred rendering the most).

 

My question is are there any other options I haven't considered? There is surpsingly a lack of documentation and literature on this matter floating around. If there are no other better options, which option do you think is best for me to choose? Alternatively, is it worth me using deferred rendering at all and should I spend my time making a more intelligent batching system/render queue and try and squeeze more frames out of there?

 

If it makes any difference I'll be using OpenGL core profile 3.3. My host language is C# / OpenTK.

0

Share this post


Link to post
Share on other sites

I'm curious - what's the motivation for doing the material buffer and the second pass expansion of shading attributes? Deferred shading is already somewhat limited in what kind of material variation you can create - but having interesting materials that control what gets painted into the gbuffer can mitigate that. Your design is going to severely limit what you can do - and you're just hitting the first example of that. Are you worried about performance, or is there some other goal here?

0

Share this post


Link to post
Share on other sites

Writing out material IDs in a first pass and then creating a G-buffer from that in a second pass then doing lighting in a third pass sounds like an overly complicated solution to a problem you don't even know you have (the problem of doing too many texture samples). How do you know writing out an entire frame buffer of material IDs is going to be faster than doing a small number of unnecessary texture samples?

 

I would ditch that idea and just use a regular deferred renderer. Write out the G-buffer in the first pass, and do lighting in the second pass. Using whatever materials your objects have during the G-buffer pass. This will let you blend the diffuse color of your terrain in the G-buffer pass just by using the correct terrain shader. No hassle. If you're concerned about wasting time drawing terrain pixels that eventually get occluded, then simply draw the terrain last. The G-buffer pass should render everything front to back, anyway, to mitigate overdraw.

 

Also, typically if one were to write out a material ID at any point in the deferred pipeline, it would be written directly into the G-buffer, and it would be used to select a set of shading parameters (specular power, surface roughness, etc etc) for the lighting pass.

0

Share this post


Link to post
Share on other sites

Performance is my largest concern. Rendering an object with 5 materials would otherwise cost 5 draw calls (1 for each material). Using material IDs, that's only 1 draw call (a material ID could be assigned per-vertex).

 

I suppose I'm probably over-thinking things and inventing unnecessary solutions to problems which haven't surfaced yet, and may never surface. The biggest thing that will help me is instancing (since I'm likely to have many trees on-screen at any given point), so in theory each material is only going to cost 1 draw call anyway if my render queue batches things intelligently enough. I don't think I can control the order in which objects are drawn via instancing though.

0

Share this post


Link to post
Share on other sites

I feel like you would need very uniform materials and/or a unique virtual texturing system for your approach to work.

You may also want to keep in mind that it's very common in games to render dynamic "decals" into your G-Buffer to handle things like scorch marks and bullet holes, and this also wouldn't play nicely with your material ID system.

0

Share this post


Link to post
Share on other sites


Performance is my largest concern. Rendering an object with 5 materials would otherwise cost 5 draw calls (1 for each material). Using material IDs, that's only 1 draw call (a material ID could be assigned per-vertex).

 

If performance is your largest concern I would stay away from deferred rendering altogether, and instead use forward rendering. I've used both in our game and although deferred allows you to do more fancy stuff it comes with a cost.

0

Share this post


Link to post
Share on other sites

Performance is my largest concern. Rendering an object with 5 materials would otherwise cost 5 draw calls (1 for each material). Using material IDs, that's only 1 draw call (a material ID could be assigned per-vertex).

 

You may disable writing to z-buffer for the other passes than the first smile.png Also, you may find a way to combine the 5 materials into one.

 

Otherwise you were talking about a terrain rendering, in BF3 they used a terrain tile cache. Instead of blending 5 materials in the g-buffer, you may render the terrain materials into a tile texture and "flatten" the materials, then in the G-buffer pass you can draw pretty complex terrains with very simple shader since the materials have been blended already. So there is no need to overcomplicate your deferred renderer. 

 

Of course, there are limitations, such as tile texture detail, but this can be fixed to certain degree with detail texturing and volume decals etc. Also, the amount of tiles will eat up some GPU memory. 

 

Cheers!

Edited by kauna
0

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  
Followers 0

  • Similar Content

    • By Toastmastern
      So it's been a while since I took a break from my whole creating a planet in DX11. Last time around I got stuck on fixing a nice LOD.
      A week back or so I got help to find this:
      https://github.com/sp4cerat/Planet-LOD
      In general this is what I'm trying to recreate in DX11, he that made that planet LOD uses OpenGL but that is a minor issue and something I can solve. But I have a question regarding the code
      He gets the position using this row
      vec4d pos = b.var.vec4d["position"]; Which is then used further down when he sends the variable "center" into the drawing function:
      if (pos.len() < 1) pos.norm(); world::draw(vec3d(pos.x, pos.y, pos.z));  
      Inside the draw function this happens:
      draw_recursive(p3[0], p3[1], p3[2], center); Basically the 3 vertices of the triangle and the center of details that he sent as a parameter earlier: vec3d(pos.x, pos.y, pos.z)
      Now onto my real question, he does vec3d edge_center[3] = { (p1 + p2) / 2, (p2 + p3) / 2, (p3 + p1) / 2 }; to get the edge center of each edge, nothing weird there.
      But this is used later on with:
      vec3d d = center + edge_center[i]; edge_test[i] = d.len() > ratio_size; edge_test is then used to evaluate if there should be a triangle drawn or if it should be split up into 3 new triangles instead. Why is it working for him? shouldn't it be like center - edge_center or something like that? Why adding them togheter? I asume here that the center is the center of details for the LOD. the position of the camera if stood on the ground of the planet and not up int he air like it is now.

      Full code can be seen here:
      https://github.com/sp4cerat/Planet-LOD/blob/master/src.simple/Main.cpp
      If anyone would like to take a look and try to help me understand this code I would love this person. I'm running out of ideas on how to solve this in my own head, most likely twisted it one time to many up in my head
      Thanks in advance
      Toastmastern
       
       
    • By fllwr0491
      I googled around but are unable to find source code or details of implementation.
      What keywords should I search for this topic?
      Things I would like to know:
      A. How to ensure that partially covered pixels are rasterized?
         Apparently by expanding each triangle by 1 pixel or so, rasterization problem is almost solved.
         But it will result in an unindexable triangle list without tons of overlaps. Will it incur a large performance penalty?
      B. A-buffer like bitmask needs a read-modiry-write operation.
         How to ensure proper synchronizations in GLSL?
         GLSL seems to only allow int32 atomics on image.
      C. Is there some simple ways to estimate coverage on-the-fly?
         In case I am to draw 2D shapes onto an exisitng target:
         1. A multi-pass whatever-buffer seems overkill.
         2. Multisampling could cost a lot memory though all I need is better coverage.
            Besides, I have to blit twice, if draw target is not multisampled.
       
    • By mapra99
      Hello

      I am working on a recent project and I have been learning how to code in C# using OpenGL libraries for some graphics. I have achieved some quite interesting things using TAO Framework writing in Console Applications, creating a GLUT Window. But my problem now is that I need to incorporate the Graphics in a Windows Form so I can relate the objects that I render with some .NET Controls.

      To deal with this problem, I have seen in some forums that it's better to use OpenTK instead of TAO Framework, so I can use the glControl that OpenTK libraries offer. However, I haven't found complete articles, tutorials or source codes that help using the glControl or that may insert me into de OpenTK functions. Would somebody please share in this forum some links or files where I can find good documentation about this topic? Or may I use another library different of OpenTK?

      Thanks!
    • By Solid_Spy
      Hello, I have been working on SH Irradiance map rendering, and I have been using a GLSL pixel shader to render SH irradiance to 2D irradiance maps for my static objects. I already have it working with 9 3D textures so far for the first 9 SH functions.
      In my GLSL shader, I have to send in 9 SH Coefficient 3D Texures that use RGBA8 as a pixel format. RGB being used for the coefficients for red, green, and blue, and the A for checking if the voxel is in use (for the 3D texture solidification shader to prevent bleeding).
      My problem is, I want to knock this number of textures down to something like 4 or 5. Getting even lower would be a godsend. This is because I eventually plan on adding more SH Coefficient 3D Textures for other parts of the game map (such as inside rooms, as opposed to the outside), to circumvent irradiance probe bleeding between rooms separated by walls. I don't want to reach the 32 texture limit too soon. Also, I figure that it would be a LOT faster.
      Is there a way I could, say, store 2 sets of SH Coefficients for 2 SH functions inside a texture with RGBA16 pixels? If so, how would I extract them from inside GLSL? Let me know if you have any suggestions ^^.
    • By KarimIO
      EDIT: I thought this was restricted to Attribute-Created GL contexts, but it isn't, so I rewrote the post.
      Hey guys, whenever I call SwapBuffers(hDC), I get a crash, and I get a "Too many posts were made to a semaphore." from Windows as I call SwapBuffers. What could be the cause of this?
      Update: No crash occurs if I don't draw, just clear and swap.
      static PIXELFORMATDESCRIPTOR pfd = // pfd Tells Windows How We Want Things To Be { sizeof(PIXELFORMATDESCRIPTOR), // Size Of This Pixel Format Descriptor 1, // Version Number PFD_DRAW_TO_WINDOW | // Format Must Support Window PFD_SUPPORT_OPENGL | // Format Must Support OpenGL PFD_DOUBLEBUFFER, // Must Support Double Buffering PFD_TYPE_RGBA, // Request An RGBA Format 32, // Select Our Color Depth 0, 0, 0, 0, 0, 0, // Color Bits Ignored 0, // No Alpha Buffer 0, // Shift Bit Ignored 0, // No Accumulation Buffer 0, 0, 0, 0, // Accumulation Bits Ignored 24, // 24Bit Z-Buffer (Depth Buffer) 0, // No Stencil Buffer 0, // No Auxiliary Buffer PFD_MAIN_PLANE, // Main Drawing Layer 0, // Reserved 0, 0, 0 // Layer Masks Ignored }; if (!(hDC = GetDC(windowHandle))) return false; unsigned int PixelFormat; if (!(PixelFormat = ChoosePixelFormat(hDC, &pfd))) return false; if (!SetPixelFormat(hDC, PixelFormat, &pfd)) return false; hRC = wglCreateContext(hDC); if (!hRC) { std::cout << "wglCreateContext Failed!\n"; return false; } if (wglMakeCurrent(hDC, hRC) == NULL) { std::cout << "Make Context Current Second Failed!\n"; return false; } ... // OGL Buffer Initialization glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT); glBindVertexArray(vao); glUseProgram(myprogram); glDrawElements(GL_TRIANGLES, indexCount, GL_UNSIGNED_SHORT, (void *)indexStart); SwapBuffers(GetDC(window_handle));  
  • Popular Now