Sign in to follow this  
bala_dbhat

OpenGL Weird GLSL Shader

Recommended Posts

I'm a beginner in the field of shaders. I'm using shaders in my application. I'm facing a weird problem while switching between OpenGL fixed functionalities and shaders. I want to render some objects using fixed pipeline and the rest using shaders. I used glUseProgramObjectARB for switching. glUseProgramObjectARB(Prog_Obj); drawShape1(); glUseProgramObjectARB(0); drawShape2(); The above method works fine if I attach both vertex and fragment shader objects to the program object. But if I attach only a vertex shader object to the program object and try to render, I get weird shapes (shape2). Rendering through shader is proper but I get the problem after switching back to fixed functionalities. I use the Apple Software Renderer (ID - 0X00020400) on Mac OS X (10.4.4) Can any1 help me out please?

Share this post


Link to post
Share on other sites
I have never made a vertex shader-only program. I always use both shaders, as I believe it to be necessary.

In the vertex shader one would create and initialize a global varying vecN variable to the desired colour. This value is linearly interpolated between the two vertices depending on where the fragment lies between them onscreen. The fragment then outputs that as the final fragment colour. In this context, a fragment is a pixel onscreen.

Your method of switching to fixed-function from shader drawing is the same code as mine, which should work. Once you have your fixed-function model and projection matrices setup, it really should line up. Also, glEnable(GL_TEXTUREnD); is essential, if not already.

P.S. The OpenGL Shading Language, Second Edition By Randi J. Rost is an excellent and up-to-date reference and tutorial for GLSL.

[Edited by - taby on May 21, 2006 2:17:30 AM]

Share this post


Link to post
Share on other sites
on 10.4.4 it works for me with hardware rendering (all machines). sometimes the software render gives strange and buggy results. try it with hardware accelerated context!

if you get the same result - how is you shader setup code?

Share this post


Link to post
Share on other sites
Using this class, I call LoadShader, then EnableShader / DisableShader. Set* is for setting uniform variables.


#ifndef SJH_GLSL_SHADER
#define SJH_GLSL_SHADER


#include <iostream>
using std::cout;
using std::endl;

#include <string>
using std::string;

#include <fstream>
using std::ifstream;

#include "gl_extensions.h"
#include "point_3.h"


class glsl_shader
{
protected:
GLint mHandleProg;
string vs_source;
string fs_source;
sjh_ext_class gl;

public:
string last_error;

glsl_shader(void);
~glsl_shader(void);

void EnableShader(void);
void DisableShader(void);
bool LoadShader(sjh_ext_class &src_gl, const char *const vs_name = 0, const char *const fs_name = 0);
void Set1i(string token, int v);
void Set1f(string token, float v);
void Set3f(string token, point_3 v);
};


#endif





#include "glsl_shader.h"

#include <cassert>

#include <vector>
using std::vector;


glsl_shader::glsl_shader(void)
{
mHandleProg = 0;
last_error = "Success";
}

glsl_shader::~glsl_shader(void)
{
if(0 != mHandleProg)
gl.glDeleteProgram(mHandleProg);
}

void glsl_shader::EnableShader(void)
{
gl.glUseProgram(mHandleProg);
last_error = "Success";
}

void glsl_shader::DisableShader(void)
{
gl.glUseProgram(0);
last_error = "Success";
}

bool glsl_shader::LoadShader(sjh_ext_class &src_gl, const char *const vs_name, const char *const fs_name)
{
gl = src_gl;

string temp_str;

if(0 != vs_name)
{
ifstream infile(vs_name);

if(infile.fail())
{
last_error = "Could not open vertex shader file: ";
last_error += vs_name;
return false;
}

while(getline(infile, temp_str))
vs_source += temp_str + '\n';
}

if(0 != fs_name)
{
ifstream infile2(fs_name);

if(infile2.fail())
{
last_error = "Could not open fragment shader file: ";
last_error += fs_name;
return false;
}

while(getline(infile2, temp_str))
fs_source += temp_str + '\n';
}

const char *cch = 0;
GLint status = GL_FALSE;

GLint mHandleVert = gl.glCreateShader(GL_VERTEX_SHADER_ARB);
GLint mHandleFrag = gl.glCreateShader(GL_FRAGMENT_SHADER_ARB);

gl.glShaderSource(mHandleVert, 1, &(cch = vs_source.c_str()), 0);
gl.glShaderSource(mHandleFrag, 1, &(cch = fs_source.c_str()), 0);

gl.glCompileShader(mHandleVert);
gl.glGetShader(mHandleVert, GL_COMPILE_STATUS, &status);

if(GL_FALSE == status)
{
last_error = "Vertex shader compile error!";
cout << last_error << endl;

GLsizei log_size = 0;

vector<GLchar> buf;
buf.reserve(4096);
buf.resize(4096, 0);

gl.glGetShaderInfoLogEXT(mHandleVert, 4096, NULL, &buf[0]);

for(size_t i = 0; i < buf.size(); i++)
if(0 != buf[i])
cout << buf[i];

gl.glDeleteShader(mHandleFrag);
gl.glDeleteShader(mHandleVert);

return false;
}

gl.glCompileShader(mHandleFrag);
gl.glGetShader(mHandleFrag, GL_COMPILE_STATUS, &status);

if(GL_FALSE == status)
{
last_error = "Fragment shader compile error!";
cout << last_error << endl;

GLsizei log_size = 0;

vector<GLchar> buf;
buf.reserve(4096);
buf.resize(4096, 0);

gl.glGetShaderInfoLogEXT(mHandleFrag, 4096, NULL, &buf[0]);

for(size_t i = 0; i < buf.size(); i++)
if(0 != buf[i])
cout << buf[i];

gl.glDeleteShader(mHandleFrag);
gl.glDeleteShader(mHandleVert);

return false;
}

mHandleProg = gl.glCreateProgram();

gl.glAttachShader(mHandleProg, mHandleVert);
gl.glAttachShader(mHandleProg, mHandleFrag);

gl.glLinkProgram(mHandleProg);

gl.glGetProgram(mHandleProg, GL_LINK_STATUS, &status);

if(GL_FALSE == status)
{
last_error = "Shader linker error!";
cout << last_error << endl;

vector<GLchar> buf;
buf.reserve(4096);
buf.resize(4096, 0);

gl.glGetShaderInfoLogEXT(mHandleProg, 4096, NULL, &buf[0]);

for(size_t i = 0; i < buf.size(); i++)
if(0 != buf[i])
cout << buf[i];

return false;
}


gl.glDetachShader(mHandleProg, mHandleFrag);
gl.glDetachShader(mHandleProg, mHandleVert);

gl.glDeleteShader(mHandleFrag);
gl.glDeleteShader(mHandleVert);

last_error = "Success";

return true;
}

void glsl_shader::Set1i(string token, int v)
{
gl.glUniform1i(gl.glGetUniformLocation(mHandleProg, token.c_str()), v);
last_error = "Success";
}

void glsl_shader::Set1f(string token, float v)
{
gl.glUniform1f(gl.glGetUniformLocation(mHandleProg, token.c_str()), v);
last_error = "Success";
}

void glsl_shader::Set3f(string token, point_3 v)
{
gl.glUniform3f(gl.glGetUniformLocation(mHandleProg, token.c_str()), v.x, v.y, v.z);
last_error = "Success";
}


Share this post


Link to post
Share on other sites
Thanks for your feed back
Currently, Im referring The OpenGL Shading Language, Second Edition By Randi J. Rost

In my case, I got to support the case of having only one shader (say vertex only).

About using hardware renderer, I'll try it..

I hav one more query..

If I enable automatic texture coord generation and try to use shaders, none of the textures are getting applied on the object.

I have made use of the examples provided in The OpenGL Shading Language, Second Edition By Randi J. Rost


Share this post


Link to post
Share on other sites
"If I enable automatic texture coord generation and try to use shaders, none of the textures are getting applied on the object. "

You need to do the texture coordinate generation yourself in the shader. In the 2nd edition there is a chapter on FFP functions such as automatic texture coordinate generation and how to do them in the shaders. HTH

Share this post


Link to post
Share on other sites
Thanks...
I could generate it now..

As you all mentioned, I have to generate the tex coords..

I could solve the vertex shader related problem (switching between fixed func & shader).

It works fine if you use hardware accelerated contexts. But software renderer still behaves strangely...

Thanks for that suggestion

[Edited by - bala_dbhat on May 23, 2006 3:53:24 AM]

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  

  • Forum Statistics

    • Total Topics
      627714
    • Total Posts
      2978773
  • Similar Content

    • By DelicateTreeFrog
      Hello! As an exercise for delving into modern OpenGL, I'm creating a simple .obj renderer. I want to support things like varying degrees of specularity, geometry opacity, things like that, on a per-material basis. Different materials can also have different textures. Basic .obj necessities. I've done this in old school OpenGL, but modern OpenGL has its own thing going on, and I'd like to conform as closely to the standards as possible so as to keep the program running correctly, and I'm hoping to avoid picking up bad habits this early on.
      Reading around on the OpenGL Wiki, one tip in particular really stands out to me on this page:
      For something like a renderer for .obj files, this sort of thing seems almost ideal, but according to the wiki, it's a bad idea. Interesting to note!
      So, here's what the plan is so far as far as loading goes:
      Set up a type for materials so that materials can be created and destroyed. They will contain things like diffuse color, diffuse texture, geometry opacity, and so on, for each material in the .mtl file. Since .obj files are conveniently split up by material, I can load different groups of vertices/normals/UVs and triangles into different blocks of data for different models. When it comes to the rendering, I get a bit lost. I can either:
      Between drawing triangle groups, call glUseProgram to use a different shader for that particular geometry (so a unique shader just for the material that is shared by this triangle group). or
      Between drawing triangle groups, call glUniform a few times to adjust different parameters within the "master shader", such as specularity, diffuse color, and geometry opacity. In both cases, I still have to call glBindTexture between drawing triangle groups in order to bind the diffuse texture used by the material, so there doesn't seem to be a way around having the CPU do *something* during the rendering process instead of letting the GPU do everything all at once.
      The second option here seems less cluttered, however. There are less shaders to keep up with while one "master shader" handles it all. I don't have to duplicate any code or compile multiple shaders. Arguably, I could always have the shader program for each material be embedded in the material itself, and be auto-generated upon loading the material from the .mtl file. But this still leads to constantly calling glUseProgram, much more than is probably necessary in order to properly render the .obj. There seem to be a number of differing opinions on if it's okay to use hundreds of shaders or if it's best to just use tens of shaders.
      So, ultimately, what is the "right" way to do this? Does using a "master shader" (or a few variants of one) bog down the system compared to using hundreds of shader programs each dedicated to their own corresponding materials? Keeping in mind that the "master shaders" would have to track these additional uniforms and potentially have numerous branches of ifs, it may be possible that the ifs will lead to additional and unnecessary processing. But would that more expensive than constantly calling glUseProgram to switch shaders, or storing the shaders to begin with?
      With all these angles to consider, it's difficult to come to a conclusion. Both possible methods work, and both seem rather convenient for their own reasons, but which is the most performant? Please help this beginner/dummy understand. Thank you!
    • By JJCDeveloper
      I want to make professional java 3d game with server program and database,packet handling for multiplayer and client-server communicating,maps rendering,models,and stuffs Which aspect of java can I learn and where can I learn java Lwjgl OpenGL rendering Like minecraft and world of tanks
    • By AyeRonTarpas
      A friend of mine and I are making a 2D game engine as a learning experience and to hopefully build upon the experience in the long run.

      -What I'm using:
          C++;. Since im learning this language while in college and its one of the popular language to make games with why not.     Visual Studios; Im using a windows so yea.     SDL or GLFW; was thinking about SDL since i do some research on it where it is catching my interest but i hear SDL is a huge package compared to GLFW, so i may do GLFW to start with as learning since i may get overwhelmed with SDL.  
      -Questions
      Knowing what we want in the engine what should our main focus be in terms of learning. File managements, with headers, functions ect. How can i properly manage files with out confusing myself and my friend when sharing code. Alternative to Visual studios: My friend has a mac and cant properly use Vis studios, is there another alternative to it?  
    • By ferreiradaselva
      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. 
  • Popular Now