• 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
Hyunkel

OpenGL
FBO Questions

10 posts in this topic

Hello,

 

I'm doing shadow mapping with exponential shadow maps (ESM) in OpenGL 4.3.

This requires blurring the shadow map, which I do with a normal 2-pass gaussian blur.

What I want to do is the following:

 

Shadow map -> (Vertical Blur Shader) -> Intermediate Texture -> (Horizontal Blur Shader) -> Shadow Map

 

The shadow map is a DepthComponent32f texture and the intermediate texture uses R32f.

The first pass works fine, but for the second pass, where I want to write back to the shadow map, I can't seem to use the shadow map as a FBO color attachment, so I'm unable to write back to it.

 
I've also noticed, completely by accident, that I can sample from a texture that I am currently writing to, without any ill results.
For example I can do:
Texture -> (Vertical Blur Shader) -> Texture
 
To recap:
  1. Is there a way to use a DepthComponent texture as a color attachment in a FBO?
  2. Why can I sample a texture that I'm currently writing to? Is this legal in OpenGL 4.3, or is the behavior undefined? What happens behind the scenes? Does it internally create a new texture to write to, and then discard the old one when the draw call finishes?

Cheers,
Hyu

0

Share this post


Link to post
Share on other sites

 

 

@Question 1: I presume you want to reuse the memory of the shadow map? Because otherwise there is no reason to to use a DepthComponent texture as the final target.

Yes, that is correct. I would like to avoid allocating an extra texture for each shadow map if possible.

 

 

 

@Question 2: The results of doing that are usually "undefined" which means anything can happen (including the intended) but the behavior can be different for different vendors, driver versions, GPU-loads, ... In short: don't do it.
The texture cache, through which you read, is not kept coherent with the video memory so writing a pixel does not effect the copy of that pixel in the texture cache, which is probably what you are seeing here. In most cases, you can read and write to the same texture, if you only read one pixel per thread and it's the very pixel you write, but in your case you are reading more than one pixel.

Makes perfect sense, thanks!

0

Share this post


Link to post
Share on other sites


Why can I sample a texture that I'm currently writing to? Is this legal in OpenGL 4.3, or is the behavior undefined?

It is explicitly not disallowed, because there are useful operations in this area (i.e. updating a particle system stored in a texture).

 

As Ohforf says, reading different pixels than you are writing is asking for trouble.

1

Share this post


Link to post
Share on other sites


Is there a way to use a DepthComponent texture as a color attachment in a FBO?
Nope. Just use GL_RED, GL_R32F with GL_FLOAT as type. Depth is just a value, write/read it as it were like any other texture (it is).
1

Share this post


Link to post
Share on other sites

 

It is explicitly not disallowed, because there are useful operations in this area (i.e. updating a particle system stored in a texture).

 

As Ohforf says, reading different pixels than you are writing is asking for trouble.

Good to know, thanks!

 

 

 

Nope. Just use GL_RED, GL_R32F with GL_FLOAT as type. Depth is just a value, write/read it as it were like any other texture (it is). 

But I can't use GL_32F as a depth attachment when generating the shadow map, can I?

0

Share this post


Link to post
Share on other sites


But I can't use GL_32F as a depth attachment when generating the shadow map, can I?
You could write the depth values yourself onto that 32 bit float texture as a regular color attachment, then sample/modify them as you please, and just attaching a regular RBO to the depth attachment.

 

Now, I'm not sure if you could actually create a depth texture, attach it to the FBO as depth attachment, and also bind it to a texture image unit and sample from it.

 

Then again, if you're doing the writing in a final pass and you don't need to simultaneously sample from the depth buffer, you could always write what you need to the depth attachment directly in the fragment shader.

1

Share this post


Link to post
Share on other sites

 

 

You could write the depth values yourself onto that 32 bit float texture as a regular color attachment, then sample/modify them as you please, and just attaching a regular RBO to the depth attachment.

 

Now, I'm not sure if you could actually create a depth texture, attach it to the FBO as depth attachment, and also bind it to a texture image unit and sample from it.

 

Then again, if you're doing the writing in a final pass and you don't need to simultaneously sample from the depth buffer, you could always write what you need to the depth attachment directly in the fragment shader.

I've tried a few more different combinations, and it seems like it is not possible to create a texture that can be used both as a depth attachment and as a color attachment.

But as you've mentioned, I can either simply output to gl_FragDepth for the final pass, or for the shadow map generation, output the depth to a color attachment, using a shared RBO across all shadow maps.

 

Thank you for all the helpful comments!

Cheers,

Hyu

0

Share this post


Link to post
Share on other sites
The hardware depth test has certain optimizations in place which can significantly speed up the rendering of occluded fragments. However, those optimizations require additional memory which is why depth attachments are more then a simple texture. You can't just use them as a regular render target, write to them, and still expect that additional memory for the optimizations to be consistent.
OpenGL actually has a method for aliasing the format of textures, called TextureView, and as far as I'm aware, even TextureViews can't change a depth texture into a regular one.

I think the best option is to allocate 3 buffers: The depth attachment, into which you render, the intermediate texture and the final texture. Note that the first 2 can be reused by other lights after the filtering, as long as the other shadowmaps have the same or a smaller size.
2

Share this post


Link to post
Share on other sites


The hardware depth test has certain optimizations in place which can significantly speed up the rendering of occluded fragments.
This. Have in mind that writing directly to the depth buffer means no early Z rejection. The GPU can "preemptively" reject fragments before executing the fragment shader by just testing the resulting depth value from the vertex shader outputs.

 

If you write to the depth buffer directly, the GPU has to execute the fragment shader to know the actual depth value, thus no early Z rejection is possible.

 

If that worries you, you can always measure the differences between the possible methods.

1

Share this post


Link to post
Share on other sites

 

 

The hardware depth test has certain optimizations in place which can significantly speed up the rendering of occluded fragments. However, those optimizations require additional memory which is why depth attachments are more then a simple texture. You can't just use them as a regular render target, write to them, and still expect that additional memory for the optimizations to be consistent.

 

 

This. Have in mind that writing directly to the depth buffer means no early Z rejection. The GPU can "preemptively" reject fragments before executing the fragment shader by just testing the resulting depth value from the vertex shader outputs.

 

If you write to the depth buffer directly, the GPU has to execute the fragment shader to know the actual depth value, thus no early Z rejection is possible.

 

The reason I initially wanted to do this is because my shadow maps for directional lights have 4 cascades, and I tried generating them simultaneously by quadrupling the geometry using  the geometry buffer. If I rendered only to the depth buffer I was able to avoid allocating an additional 4 R32f 2048x2048 color attachment slices.

After some profiling I noticed that this isn't really any faster than generating the cascades in individual passes though, provided that I use decent frustum culling for the individual cascades.

 

 

 

I think the best option is to allocate 3 buffers: The depth attachment, into which you render, the intermediate texture and the final texture. Note that the first 2 can be reused by other lights after the filtering, as long as the other shadowmaps have the same or a smaller size. 

This is precisely what I am doing now. It is also much easier to have either a linear or exponential shadow map this way, which is needed for ESM.

 

Thanks again!

Hyu

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 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));  
    • By Tchom
      Hey devs!
       
      I've been working on a OpenGL ES 2.0 android engine and I have begun implementing some simple (point) lighting. I had something fairly simple working, so I tried to get fancy and added color-tinting light. And it works great... with only one or two lights. Any more than that, the application drops about 15 frames per light added (my ideal is at least 4 or 5). I know implementing lighting is expensive, I just didn't think it was that expensive. I'm fairly new to the world of OpenGL and GLSL, so there is a good chance I've written some crappy shader code. If anyone had any feedback or tips on how I can optimize this code, please let me know.
       
      Vertex Shader
      uniform mat4 u_MVPMatrix; uniform mat4 u_MVMatrix; attribute vec4 a_Position; attribute vec3 a_Normal; attribute vec2 a_TexCoordinate; varying vec3 v_Position; varying vec3 v_Normal; varying vec2 v_TexCoordinate; void main() { v_Position = vec3(u_MVMatrix * a_Position); v_TexCoordinate = a_TexCoordinate; v_Normal = vec3(u_MVMatrix * vec4(a_Normal, 0.0)); gl_Position = u_MVPMatrix * a_Position; } Fragment Shader
      precision mediump float; uniform vec4 u_LightPos["+numLights+"]; uniform vec4 u_LightColours["+numLights+"]; uniform float u_LightPower["+numLights+"]; uniform sampler2D u_Texture; varying vec3 v_Position; varying vec3 v_Normal; varying vec2 v_TexCoordinate; void main() { gl_FragColor = (texture2D(u_Texture, v_TexCoordinate)); float diffuse = 0.0; vec4 colourSum = vec4(1.0); for (int i = 0; i < "+numLights+"; i++) { vec3 toPointLight = vec3(u_LightPos[i]); float distance = length(toPointLight - v_Position); vec3 lightVector = normalize(toPointLight - v_Position); float diffuseDiff = 0.0; // The diffuse difference contributed from current light diffuseDiff = max(dot(v_Normal, lightVector), 0.0); diffuseDiff = diffuseDiff * (1.0 / (1.0 + ((1.0-u_LightPower[i])* distance * distance))); //Determine attenuatio diffuse += diffuseDiff; gl_FragColor.rgb *= vec3(1.0) / ((vec3(1.0) + ((vec3(1.0) - vec3(u_LightColours[i]))*diffuseDiff))); //The expensive part } diffuse += 0.1; //Add ambient light gl_FragColor.rgb *= diffuse; } Am I making any rookie mistakes? Or am I just being unrealistic about what I can do? Thanks in advance
    • By yahiko00
      Hi,
      Not sure to post at the right place, if not, please forgive me...
      For a game project I am working on, I would like to implement a 2D starfield as a background.
      I do not want to deal with static tiles, since I plan to slowly animate the starfield. So, I am trying to figure out how to generate a random starfield for the entire map.
      I feel that using a uniform distribution for the stars will not do the trick. Instead I would like something similar to the screenshot below, taken from the game Star Wars: Empire At War (all credits to Lucasfilm, Disney, and so on...).

      Is there someone who could have an idea of a distribution which could result in such a starfield?
      Any insight would be appreciated
  • Popular Now