• 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
Prune

OpenGL
Depth pre-pass: does OpenGL still execute fragment shader if depth not written and color mask is GL_NONE?

13 posts in this topic

I set up for depth pre-pass as follows:

glEnable(GL_DEPTH_TEST);
glDepthMask(GL_TRUE);
glDepthFunc(GL_LESS);
glClear(GL_DEPTH_BUFFER_BIT);
glFramebufferDrawBufferEXT(id, GL_NONE); // id is currently bound framebuffer object
glColorMaski(0, GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);

I'm not explicitly writing depth in the fragment shader. Should I then have a version of my shader program that has only a vertex shader and no fragment shader? I ask for efficiency reasons, since I don't know whether OpenGL can figure out from either the GL_NONE draw buffer or false color mask that it doesn't need to run the fragment shader. The downside of doing a separate shader program for the depth pre-pass is that I'd have to do it for every shader program that has a different vertex shader.

0

Share this post


Link to post
Share on other sites

Kind of a useless question.

If it does execute: then keep your fragment shader as gl_FragColor = vec4(0,0,0,0);  OR you may not even need it. leaving a blank main() that returns immediately even though it is executed.

If it doesn't execute for GL_NONE: then keep the same stripped down fragment shader. It just wont run.....

I don't believe you can have a shader object without a vertex + pixel shader. Not sure though.

-4

Share this post


Link to post
Share on other sites

First off, you ask "if depth not written" - and then you use glDepthMask(GL_TRUE) - that's oxymoronic.

 

Secondly, for a final absolute determination... you can use a query object for samples passed.

1

Share this post


Link to post
Share on other sites

Kind of a useless question.

If it does execute: then keep your fragment shader as gl_FragColor = vec4(0,0,0,0);  OR you may not even need it. leaving a blank main() that returns immediately even though it is executed.

If it doesn't execute for GL_NONE: then keep the same stripped down fragment shader. It just wont run.....

I don't believe you can have a shader object without a vertex + pixel shader. Not sure though.

 

Maybe you should read the question again, because you seem to have answered a different one.

 

> If it does execute...

> If it doesn't execute

 

That presumes the answer--which, if I knew, I wouldn't have asked here in the very title of my question, now, would have I? Do you have a problem with reading comprehension?

 

I specifically asked about efficiency. I need to know which case it is, so I can determine whether to do the work of making additional shader programs that have the no fragment shader (or have a main() that doesn't do anything--which of those latter two is NOT my question and obviously I can easily check). What you wrote, instead, was what to do in either case--which I already knew. GG

Edited by Prune
-1

Share this post


Link to post
Share on other sites

First off, you ask "if depth not written" - and then you use glDepthMask(GL_TRUE) - that's oxymoronic.

 

Secondly, for a final absolute determination... you can use a query object for samples passed.

I mean not written explicitly in the fragment shader by assigning to gl_FragDepth.

1

Share this post


Link to post
Share on other sites

Impossible to tell for sure, but probably yes.

 

In theory, the fragment shader should run, since whether or not you enable writing out fragments using glColorMaski doesn't matter for the shader. Masking happens after execution of the fragment shader, and it is also orthogonal (in times of atomic ops and shader load/store, a shader can have side effects even if not outputting any depth or color values to fragments).

 

In practice, who knows. The driver might simply realize that nothing happens (depth is not written in the shader, and color is masked out) and not execute the shader at all. If your application has a noticeable market share, the IHV might even come up with a driver profile for your application which enables that optimization only for your application.

 

First off, you ask "if depth not written" - and then you use glDepthMask(GL_TRUE) - that's oxymoronic.
The meaning is (at least I'd guess so) that depth is written as the interpolated vertex depth, and not calculated by the fragment shader. Edited by samoth
1

Share this post


Link to post
Share on other sites

 

Impossible to tell for sure, but probably yes.

 

In theory, the fragment shader should run, since whether or not you enable writing out fragments using glColorMaski doesn't matter for the shader. Masking happens after execution of the fragment shader, and it is also orthogonal (in times of atomic ops and shader load/store, a shader can have side effects even if not outputting any depth or color values to fragments).

 

In practice, who knows. The driver might simply realize that nothing happens (depth is not written in the shader, and color is masked out) and not execute the shader at all. If your application has a noticeable market share, the IHV might even come up with a driver profile for your application which enables that optimization only for your application.

 

 

 

First off, you ask "if depth not written" - and then you use glDepthMask(GL_TRUE) - that's oxymoronic.
The meaning is (at least I'd guess so) that depth is written as the interpolated vertex depth, and not calculated by the fragment shader.

 

Thanks. And yes, that's what I meant with "depth not written".

0

Share this post


Link to post
Share on other sites

 

does OpenGL still execute fragment shader if depth not written and color mask is GL_NONE?

 

And what exactly did I say......... I will add you to the list of people I choose not to help, which will be 1 person for the last 8 years I've been on here.

I gave you some logical thinking which is: who cares. If the GPU does or doesn't run the pixel shader, then whatever shader you have bound wont run anyway (Even if its 1 million executions). If the contrary to that is it does run, then give it the simplest shader possible. Same result, and you don't even need to know the answer to your question................because it doesn't matter. Its either going to execute your 0 or 1 instruction pixel shader or not. Its out of your control, but if you assume it has to run a pixel shader, then you are safe. NOT TO MENTION it could be vendor/card specific under the hood to decide to use the pixel shader or not.

How hard is if for you to write a pixel shader that does 20 texture fetches with glDrawBuffers(GL_NONE) and see if your performance is horrible.....well then its running your pixel shader......

 

Do you have a problem with reading comprehension?

When people (who work in the industry already) reply to you and give you a decent answer and tell them they are too stupid that they can't even read your question, so they shouldn't help you.....

Edited by dpadam450
-3

Share this post


Link to post
Share on other sites
Instead of answering the question (because I don't know) I'll just suggest you use `glDrawBuffer(GL_NONE)` to explicitly tell it not to draw to a color buffer. I dont use a fragment shader with this setting and Everything runs great.
0

Share this post


Link to post
Share on other sites

as Hodge man said, in case you alter gl_FragCoord, pixel function is run even if zfail occurs. In case you dont, rendering z prepass will mean writing to depth buffer, so pixel function will run if z passes. If you have an extensive instruction you do not wish to run in it computing colors, use a another program with rather empty pixel function, I do not see a big problem setting a program once a frame to generate zprepass. I gess that only in case of colormask false, depthmask false and stencil mask false will driver not perform pixel function, but that would mean not performing actual draw call, what is not a case of depth writing zprepass.

0

Share this post


Link to post
Share on other sites

Should I then have a version of my shader program that has only a vertex shader and no fragment shader? [...] The downside of doing a separate shader program for the depth pre-pass is that I'd have to do it for every shader program that has a different vertex shader.


I think you should be able to reuse the shaders for the shadow map generation, so you don't need an additional version (or rather, you need it anyways for the shadows).

As to whether or not you should use seperate versions in the first place: I don't have actual numbers, but a vertex program reads a lot of attributes (texture coordinates, normals, tangents, ...) that you don't need for shadow maps/z pre pass. The driver might be able to detect, that the fragment program can be disabled, and that it doesn't need the interpolants for those attributes, but my guess is that it won't recompile the vertex program to strip out all the unnecessary attribute reading and (possibly) transforming.
Also, most shaders only vary in the fragment part and using a seperate shader for shadow map/z pre pass should allow the renderer to issue less shader program changes or even merge entire draw calls.
So I would expect to see a performance speedup from seperate shader versions, but again: I don't have any real numbers to prove it.
1

Share this post


Link to post
Share on other sites

[...] Same result, and you don't even need to know the answer to your question................because it doesn't matter. Its either going to execute your 0 or 1 instruction pixel shader or not.


Actually I seem to recall that a certain widely used GPU could render at twice it's normal speed when fragment programs were explicitely disabled. On that GPU, the 0 or 1 instruction pixel shader would slow down rendering to half the possible speed.
0

Share this post


Link to post
Share on other sites

Actually I seem to recall that a certain widely used GPU could render at twice it's normal speed when fragment programs were explicitely disabled. On that GPU, the 0 or 1 instruction pixel shader would slow down rendering to half the possible speed.

That was nVidia GPUS, a long time ago (like... Geforce 8 or so, possibly even Geforce 6).

 

 

In general, that same thing is of course still true, but not as such a clear-cut 1:2 thing. The time it takes to complete a frame is the time it takes to process the vertices and run other gimmicks such as geo shader or tesselation, and then shade fragments, and finally push the output trough ROPs.

 

While ALU (that is, shaders) has gone up tremendously, ROP is more or less the same as it was 5 or 10 years ago, so this matters a lot more.

 

Depending on how the ROPs work on a partiuclar card (ALU is nowadays scalar, so processing 4 values isn't the same as processing 1 value any more, it might be similar for ROPs, or very different -- I can't tell), it may make virtually no difference at all, or a huge difference. Imagine that a ROP can pass a 4-vector plus depth plus stencil (6 values total) during one clock cycle, or 6 depth-only values (also 6 values total). Or, imagine that it processes one output pixel with up to 16 (or any other number) values.

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