# OpenGL From Vertex Shader back to OpenGL-Transformation ?

## Recommended Posts

Hi there ! I just have programmed a custom vertex shader for my OpenGL-based game. But now I want to make it run even on graphic cards which are not able to load custom vertex shaders. So I want to compute all necessary transformations on the CPU. My Problem is, that I have to transform ALL Vertices (or Polygons) in my scene by a 4x4-matrix, which has to be recomputed every frame. Does anybody know which OpenGL-methods to use ? Do I have to modify the OpenGL-modelview-matrix or the projection matrix ? I am currently quite desperate about this issue, I hope somebody knows a option how to "migrate" a vertex shader back to the CPU.

##### Share on other sites
Quote:
 Original post by putenuterHi there !I just have programmed a custom vertex shader for my OpenGL-based game.But now I want to make it run even on graphic cards which are not able to load custom vertex shaders. So I want to compute all necessary transformations on the CPU.My Problem is, that I have to transform ALL Vertices (or Polygons) in my scene by a 4x4-matrix, which has to be recomputed every frame.Does anybody know which OpenGL-methods to use ? Do I have to modify the OpenGL-modelview-matrix or the projection matrix ? I am currently quite desperate about this issue, I hope somebody knows a option how to "migrate" a vertex shader back to the CPU.

Transform all vertices by a 4x4 matrix? That would very likely be the modelview matrix (load it with glLoadMatrix).
What is the purpose? Camera class? If it's a camera class, then yes, go for modelview.

##### Share on other sites
I just have programmed a custom vertex shader for my OpenGL-based game.
But now I want to make it run even on graphic cards which are not able to load custom vertex shaders. So I want to compute all necessary transformations on the CPU.

##### Share on other sites
First of all, cross-posting is not good.

Second, why do you need a vertex shader for something so simple as transforming the vertices with a matrix? You are aware that vertex shaders is not the beginning of vertex transformations, right? There was life before them. It seems to me that you jumped directly to shaders without understanding the traditional pipeline first. You can compute the matrix and use glLoadMatrix() or glMultMatrix() to load it or multiply it with the current matrix respectively.

Third, what do you mean if you have to use the projection or the modelview matrix? It depends what is it that you want to do. It's probably the modelview, but if you have to ask you need to go back to the Red Book and learn the basics first well before you start messing with such advanced topics as shaders.

## Create an account

Register a new account

• ## Partner Spotlight

• ### Forum Statistics

• Total Topics
627678
• Total Posts
2978605
• ### Similar Content

• Both functions are available since 3.0, and I'm currently using glMapBuffer(), which works fine.
But, I was wondering if anyone has experienced advantage in using glMapBufferRange(), which allows to specify the range of the mapped buffer. Could this be only a safety measure or does it improve performance?
Note: I'm not asking about glBufferSubData()/glBufferData. Those two are irrelevant in this case.
• By xhcao
Before using void glBindImageTexture(    GLuint unit, GLuint texture, GLint level, GLboolean layered, GLint layer, GLenum access, GLenum format), does need to make sure that texture is completeness.
• By cebugdev
hi guys,
are there any books, link online or any other resources that discusses on how to build special effects such as magic, lightning, etc. in OpenGL? i mean, yeah most of them are using particles but im looking for resources specifically on how to manipulate the particles to look like an effect that can be use for games,. i did fire particle before, and I want to learn how to do the other 'magic' as well.
Like are there one book or link(cant find in google) that atleast featured how to make different particle effects in OpenGL (or DirectX)? If there is no one stop shop for it, maybe ill just look for some tips on how to make a particle engine that is flexible enough to enable me to design different effects/magic
let me know if you guys have recommendations.
• By dud3
How do we rotate the camera around x axis 360 degrees, without having the strange effect as in my video below?
Mine behaves exactly the same way spherical coordinates would, I'm using euler angles.
Tried googling, but couldn't find a proper answer, guessing I don't know what exactly to google for, googled 'rotate 360 around x axis', got no proper answers.

References:
Code: https://pastebin.com/Hcshj3FQ
The video shows the difference between blender and my rotation:

• By Defend
I've had a Google around for this but haven't yet found some solid advice. There is a lot of "it depends", but I'm not sure on what.
My question is what's a good rule of thumb to follow when it comes to creating/using VBOs & VAOs? As in, when should I use multiple or when should I not? My understanding so far is that if I need a new VBO, then I need a new VAO. So when it comes to rendering multiple objects I can either:
* make lots of VAO/VBO pairs and flip through them to render different objects, or
* make one big VBO and jump around its memory to render different objects.
I also understand that if I need to render objects with different vertex attributes, then a new VAO is necessary in this case.
If that "it depends" really is quite variable, what's best for a beginner with OpenGL, assuming that better approaches can be learnt later with better understanding?

• 12
• 12
• 10
• 12
• 22