Re: [PyOpenGL-Users] Using framebuffers

[Uğur G. <ugu...@gm...>]

I did some more research.

It looks like the EXT-framebuffer is deprecated:
https://www.opengl.org/wiki/Framebuffer_Object#EXT_Framebuffer_object
"EXT_Framebuffer_object Warning: This section describes legacy OpenGL APIs
that have been removed from core OpenGL 3.1 and above" Hence, I assume that
I should be good to go with non-EXT version.

I also tried GLUT instead of GLFW, but that didn't solve my problem. I
guess the library to create the window is not related to the framebuffer
issue.

I uploaded a newer version where you can choose between GLFW and GLUT, and
between using offscreen framebuffer or not (via global variables
WINDOW_LIBRARY and TRY_FRAMEBUFFER) here:
https://gist.github.com/vug/2c7953d5fdf750c727af249ded3e9018

This is how I generate the framebuffer.

fbo = GLuint()
glGenFramebuffers(1, fbo)
glBindFramebuffer(GL_FRAMEBUFFER, fbo)

texture = GLuint()
glGenTextures(1, texture)
glBindTexture(GL_TEXTURE_2D, texture)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, SIDE, SIDE, 0, GL_RGB,
GL_UNSIGNED_BYTE, None)
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
texture, 0)

rbo = GLuint()
glGenRenderbuffers(1, rbo)
glBindRenderbuffer(GL_RENDERBUFFER, rbo)
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, SIDE, SIDE)
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT,
GL_RENDERBUFFER, rbo)

if not glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE:
    print('framebuffer binding failed')
    exit()
glBindFramebuffer(GL_FRAMEBUFFER, 0)
glBindTexture(GL_TEXTURE_2D, 0)
glBindRenderbuffer(GL_RENDERBUFFER, 0)

Best,
u

On Sat, May 28, 2016 at 1:10 PM, Uğur Güney <ugu...@gm...> wrote:

> Thanks for your response and sharing your code!
>
> I started looking at your code. You are using from OpenGL.GL.EXT
> extensions by importing
>
> from OpenGL.GL.EXT.framebuffer_object import *
>
> I don't know what GL extensions are for in pyopengl, however, I tried to
> move from non-extension version to EXT versions of GL functions.
> Unfortunately, just at the beginning, calling the glGenFramebuffersEXT via
>
> fbo = glGenFramebuffersEXT(1)
>
> generates this error:
>
> OpenGL.error.NullFunctionError: Attempt to call an undefined function
> glGenFramebuffersEXT, check for bool(glGenFramebuffersEXT) before calling
>
> Also bool(glGenFramebuffersEXT) return False,
> whereas bool(glGenFramebuffers) is True.
>
> I am using GLFW to generate the window, and my opengl version on OSX is
> 4.1. You are using pygame for that purpose. Do you think that might be the
> source of my problem?
>
> I wasn't able to "pip install pygame" to install pygame, hence I am
> hesitant to use it. But I'll try glut and other window generation options
> to see whether framebuffer's work in them, or whether EXT functions can be
> called. Does this make sense?
>
> PS:
> By the way, I saw your amazing explanation on why y-axis should mean
> upwards direction on your website: "Part of the problem was that Blender,
> like many other modeling softwares use z  for up, which is morally wrong
> (TL;DR: If y  is "up" in 2D (clue: it is), then it should also be "up" in
> 3D; it's demented to redefine it to mean something literally orthogonal to
> its original meaning when you simply add a new coordinate)" Even though, as
> a physicist, I am in the "z is up" camp, I appreciated the persuasion power
> and simplicity of your argument. Also, my girlfriend agrees with you. :-)
>
> Have a good day!
> u
>
> On Fri, May 27, 2016 at 8:44 PM, Ian Mallett <ia...@ge...> wrote:
>
>> On Fri, May 27, 2016 at 5:35 PM, Uğur Güney <ugu...@gm...> wrote:
>>
>>> I am a beginner who studies OpenGL using PyOpenGL. I want to learn
>>> post-processing effects and as the first step I want to be able to render a
>>> scene into a FBO and then render that FBO on a quad that cover the whole
>>> screen.
>>>
>>> The python code I am running is this:
>>> https://gist.github.com/vug/2c7953d5fdf750c727af249ded3e9018 I combined
>>> parts from several tutorials I found on the internet.
>>>
>>
>>
>>> I appreciate if anyone can direct me on how to render on an offscreen
>>> framebuffer via PyOpenGL.
>>>
>>
>> ​As another reference, you may like to consider some of my code. For
>> example, I wrote a Game of Life simulator
>> <http://geometrian.com/programming/projects/index.php?project=Game%20of%20Life>
>> that uses FBOs (it actually uses two IIRC; feedback requires ping-ponging).
>> The code is well-abstracted and reasonably well-tested, so it should serve
>> as a good example.
>>
>> Ian​
>>
>
>