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bala_dbhat

OpenGL Weird GLSL Shader

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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?

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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]

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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?

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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)
cout << buf;

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)
cout << buf;

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)
cout << buf;

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";
}


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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


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"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

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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]

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