i dont really care about the vertex shader, I know the basics of creating opengl projects with glfw and glad, but the online setup guides seem to always use the vertex shaders for stuff outside of my interests
#how do i setup opengl for purely fragment shaders
pure anchor
spark beacon
You can't use a fragment shader without a vertex shader
You could draw a full screen triangle with your vertex shader, then do whatever in your fragment shader
You might also be interested in compute shaders
pure anchor
i came from shadertoy so i honestly have no idea what im doing
pure anchor
You could draw a full screen triangle with your vertex shader, then do whatever ...
yea im not interested in rendering stuff through the vertex shader, im ok with the bare minimum to get the fragment shader working
i'd just like to experiment with ray and path tracing
spark beacon
You probably want compute shaders, then. You can do whatever you want in the shader, then write colors to one or more storage images
feral rain
You can also just render to a fullscreen triangle/quad
But yeah for ray and path tracing compute might be better in the long run
You will have to learn the API at least somewhat to use it though since you're still going to need to be experienced with buffers and the way data is passed to the pipeline so I would recommend with just following the first few chapters of LearnOpenGL to get to that point
And then you'll know everything you need to whip up an environment that's good for RT
pure anchor
You will have to learn the API at least somewhat to use it though since you're s...
I've stopped at around the VBO/VAO stuff because i knew i would never wanna use that
I'll go look at what compute shaders are
feral rain
VBOs are just buffers
pure anchor
yeah, so near the end of "Hello Triangle"
feral rain
Which you will need to be intimately familiar with to have any hope of doing serious raytracing
Since that's where you'll be organizing all your data
pure anchor
isnt it all contained in the fragment shader tho
pure anchor
why would i have to organize any data outside of it
feral rain
What kind of raytracing are you referring to
Raytracing against geometry? Or just doing SDF stuff like shadertoy
pure anchor
path tracing with accumulating a buffer then averaging the color in the main
feral rain
I would look into raytracing in one weekend or scratchapixel first then
You need to learn how to do it in software before trying to make a GPU implementation
pure anchor
i already know how to do it i just have no clue how to implement it in openGL
feral rain
You've written software path tracers?
pure anchor
yes
feral rain
It's not any different mathematically but you need to put all your geometry and acceleration structure into GPU buffers so that they can be accessed as SSBOs in a compute shader
I'm not aware of any guides that teach only the bare minimum necessary for raytracing, I would just progress through the normal usage of the API for a while
pure anchor
alreight
feral rain
Once you have gotten to UBOs in learnopengl then you can skip to the parts about offscreen rendering and compute shaders
You can put all those things together to implement raytracing
spark beacon
I believe Raytracing in one Weekend talks about an acceleration structure
Might be Raytracing: The Next Week
feral rain
I'm assuming he's done acceleration structures before
If not then yeah you'll want to learn that on the CPU first
GPU raytracing is a pain in the ass
pure anchor
I'm assuming he's done acceleration structures before
idk what that is
I only ever done stuff in shadertoy
feral rain
I thought you said you wrote a software path tracer
pure anchor
in shader toy
feral rain
No I mean like in C++
pure anchor
nahw
feral rain
You said you want to trace against geometry right?
pure anchor
like spphere and triangle intersetions? yeas
feral rain
That requires a ton of work to get running in a performant way
There will be a lot of work involved on the host side to get your data packaged into structures that allow for performant tracing on the GPU
pure anchor
damn , so should i still use opengl?
feral rain
I don't really know what your goals are
But it sounds like you aren't aware that 90% of real graphics programming happens outside of the shaders
It's only shadertoy where it's all inside the shaders because there is no host application there
pure anchor
i see, I guess I can just create a triangle covering the display. I'll keep going with the regular tutorial path, then see how I can transform it for my interests
feral rain
Triangle covering the screen is the same, the way you generate the shader invocations doesn't matter
Either way your shader invocations are going to be tracing rays against an acceleration structure of your own construction
If you try to have each invocation just naively recursively trace rays against a flat buffer of geometry it's just going to hang your GPU and get your application killed by the driver lol
pure anchor
oh ok, I just thought the gpu could compute the same equation(fragment shader) much faster and parallelized than a cpu and thats all. Thank you
feral rain
It can but it's not that simple, the calculation is not very parallel because the rays become incoherent which the GPU struggles with due to its execution model
So for a scene of any complexity you still can't just naively trace rays
Especially recursively
pure anchor
i see
rose fog
You do not need any VBO/VAOs to draw a full-screen triangle, tbh
feral rain
No but you will be waist-deep in buffers in general which was why I was saying you'll eventually just need to understand the API in general
It seems unlikely to me that you could find yourself an expert in dealing with buffers and memory in GL without having ever learned the basics of the API along the way
pure anchor
true
timid coyote
You can't use a fragment shader without a vertex shader
actually you can, it just writes (0,0,0,1) into gl_Position and calls it a day. you can see this if you render with GL_POINTS :p
anyway no buffers are needed for this. hardcode your vertices in your vertex shader and index then with gl_VertexID
glDrawArrays works just fine
you'll need a VAO bound, but it can be empty
spark beacon
That sounds like a Nvidia quirk
Chapter 11 of the spec states If the current vertex stage program object has no vertex shader, or no program object is current for the vertex stage, the results of programmable vertex processing are undefined
"undefined" means "Nvidia can emit 0, 0, 0, 1"
timid coyote
hmm maybe
figured that was cannon behaviour since that's what it does for disabled vertex arrays
anyway this just so happens to be one of the extremely few things i actually managed to write about lol
pure anchor
anyway no buffers are needed for this. hardcode your vertices in your vertex sha...
yea well my vertices doesnt render more than one triangle for some reason, ive been following learnOpenGL
timid coyote
if all you want is to play with fragment shaders then you can skip that
pure anchor
yea but i need the two triangels for the dipsplay
timid coyote
yes, you can do hardcode that in your vertex shader
timid coyote
https://manpat.github.io/tutorial/ch01_speedrun_rendering.html
see ^^^
pure anchor
but then i dont know what i need and dont need in my main
Im like below noob in openGL and cpp
timid coyote
if you want to learn how to use opengl then keep following learnopengl
pure anchor
yay
timid coyote
https://manpat.github.io/tutorial/ch01_speedrun_rendering.html
if all you want is to mess with frag shaders and that's it, then this is your shortcut
buffers aren't technically required for that
pure anchor
ig but its cool without shortcuts
timid coyote
it all depends on what your goal is
timid coyote
solved?
pure anchor
silly me
timid coyote
lol
pure anchor
I'll skip EBO stuff
timid coyote
from the looks of things you can skip the third component of your vertices too
pure anchor
wat
ohh
true
Do i really have to turn the shader code into this weird thing every time
timid coyote
no
you can load shaders from disk just fine
or use raw strings
people who write shaders like this still just enjoy hurting themselves
pure anchor
how
timid coyote
I'm sure you are capable of figuring that out without my help :^)
timid coyote
Do i really have to turn the shader code into this weird thing every time
btw gl_Position = vec4(aPos, 1.0); also works
no need to spell it out
timid coyote
supported since the beginning :)
pure anchor
oh i see i cant pass gl_Position
timid coyote
pass?
pure anchor
out from the vertex shader in to the fragment