• Advertisement
Sign in to follow this  

OpenGL glFrameBufferRenderBuffer vs glFrameBufferTexture2D...FIGHT!

This topic is 1049 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

I've had problems trying to use glFrameBufferRenderBuffer and glRenderBufferStorage before when experimenting with depth textures and deferred rendering etc. Usually in tutorials I'll see code using the above functions to initialize a framebuffer object.

 

However after seeing a tutorial on deferred rendering that used glFramebufferTexture2D with a GL_DEPTH_STENCIL attachment - and this worked perfectly for me.

Doing some background reading here (http://www.songho.ca/opengl/gl_fbo.html#renderbuffer) it is suggested that:

 

 

 

Renderbuffer is simply a data storage object containing a single image of a renderable internal format. It is used to store OpenGL logical buffers that do not have corresponding texture format, such as stencil or depth buffer.

 

However if you can just use glFrameBufferTexture2D anyway then what is the purpose or need of render buffers?

Share this post


Link to post
Share on other sites

However if you can just use glFrameBufferTexture2D anyway then what is the purpose or need of render buffers?

You can use the texture version (if supported), sure, but it is not always necessary. You need textures whenever you want to access the data directly in a shader, whereas if you just need to use the buffer during rendering (eg. depth/stencil), then there is no need for a texture. In short:

Input: Texture

Output: Buffer

Input/Output: BufferTexture

Edited by Ashaman73

Share this post


Link to post
Share on other sites

However if you can just use glFrameBufferTexture2D anyway then what is the purpose or need of render buffers?

Only renderbuffers can be presented to the screen.
Renderbuffers are write-only and optimized thusly.

Most render-targets need to have read access (in 99% of cases you are writing to a render-target with the intent of reading back the results later, often for shadow mapping or post-processing), so most of the time you should (must) use a texture.
But when you don’t need to read the results (using a depth buffer for an off-screen render when you only need to read back the color result, not the depth result) you should always use a renderbuffer. They are more efficient for that purpose.


L. Spiro

Share this post


Link to post
Share on other sites

Thank you both. Ok I see. "I think." So in the case of a deferred render where there is no post process step and the final image is just a blend of the pixels affected by lights I can just present that to the screen directly and not need to render it to a full screen quad?

To elaborate if I perform a deferred render like this:

 

g buffer -> render lights via stencil testing sphere meshes against depth values to a color attachment texture -> render to full screen quad 

 

I can make it like this

 

g buffer -> render lights via stencil testing sphere meshes against depth values to a color attachment render buffer -> present render buffer to screen direct

Am I barking up the right tree?
Or totally lost the plot?

Share this post


Link to post
Share on other sites

In order to see the final result on of your rendering..no matter how its done, you will have to draw to the windowing system provided backbuffer( if you don't care about depth ) and color buffer, there is no present render buffer to screen. Render buffers are for offscreen rendering as describe above.

Share this post


Link to post
Share on other sites

Am I barking up the right tree?
Or totally lost the plot?

Well...

 

 

 


So in the case of a deferred render where there is no post process step and the final image is just a blend of the pixels affected by lights I can just present that to the screen directly and not need to render it to a full screen quad?

There are some missunderstandings. A deferred renderer utilize 80% of the time post-processing and you don't render to a fullscreen quad.

 

First try to abstract from textures/buffers etc, you have just memory.

A deferred render pipeline works like this:

1. render all the position information (which pixel represents a world position) to a buffer , called g-buffer.

2. now apply lot of post-processing steps, which take as input the g-buffer, calculate some effects (lighting, ssao, shadow) and write it back to some other memory block/buffer

3. finish it with a final pass, where you take all necessary input buffers (light, shadow, ssao, etc.) and compose a final image, write it to some memory block/buffer.

4. display this block/buffer

 

The trick is, that you use the memory blocks sometimes as output and sometimes as input (to make it simple first, you can't use a memory block for reading and writing at the same time!). Now, to translate this to OpenGL and a graphics API, you need to know, that accessing the memory blocks works like this:

1. if you want to read from it, you need handle it as texture.

2. if you want to write to it, you need to handle it as buffer.

3. if you want to sometimes read and sometimes to write to it, you need to handle it as texture and buffer.

4. To read from, you render a screensized quad and take as texture the input buffers. This way you get access to the memory blocks you want to read from. Then you do some crazy calculation in your shader and write the result to the attached memory in form of an attached buffer.

5. The texture and buffers are just an other way to access one and the same memory block.

 

Hope this helps.

Edited by Ashaman73

Share this post


Link to post
Share on other sites

btw if you want to copy from one render target to the other you can use glBlitFramebuffer, it does a copy operation from the GL_READ_FRAMEBUFFER to GL_DRAW_FRAMEBUFFER directly. Which means that you dont need to bind a shader, nor a VAO nor issue a draw call to do a fullscreen pass to copy the pixels.

Share this post


Link to post
Share on other sites

So in the case of a deferred render where there is no post process step and the final image is just a blend of the pixels affected by lights I can just present that to the screen directly and not need to render it to a full screen quad?

There are some missunderstandings. A deferred renderer utilize 80% of the time post-processing and you don't render to a fullscreen quad.

 

 

I'd like to clarify this above statement - where I said "post process" step I meant AFTER the light blending into the render target. E.g DOF, SSAO etc

So I meant - present the rendered image to the screen directly after blending all the light volumes into the scene

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • 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
  • Popular Now

  • Advertisement