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OpenGL triangle example

OpenGL
Started by Dark Engineer Jan 22, 2013 at 5:41 PM 8 replies 2.6k views
Original Post
Dark Engineer
Dark Engineer
I have problem with this code because it doesn't show anything in a window, vertex and fragment shaders are loading successfully but glGetError shows something wrong is here. Please someone help me.

#include "loadshader.h"
int main()
{
	glfwInit();
	glfwOpenWindowHint(GLFW_OPENGL_VERSION_MAJOR, 3);
	glfwOpenWindowHint(GLFW_OPENGL_VERSION_MINOR, 3);
	glfwOpenWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	glfwOpenWindowHint(GLFW_WINDOW_NO_RESIZE, GL_TRUE);
	glfwOpenWindow(800, 600, 0, 0, 0, 0, 0, 0, GLFW_WINDOW);
	glfwSetWindowTitle("Crion World Alpha");
	glewExperimental = GL_TRUE;
	glewInit();
	GLuint vertexBuffer;
	glGenBuffers( 1, &vertexBuffer );
	GLuint vao;
	glGenVertexArrays(1, & vao);
	glBindVertexArray( vao );
	GLuint vbo;
	glGenBuffers( 1, &vbo); //generate 1 buffer
	float vertices[] = {
		0.0f,	0.5f,
		0.5f,	-0.5f,
		-0.5f,	-0.5f
	};
	glBindBuffer( GL_ARRAY_BUFFER, vbo );
	glBufferData( GL_ARRAY_BUFFER, sizeof( vertices ), vertices, GL_STATIC_DRAW );
	// vertex shader loading
	const string vShaderString = loadShaderFile("SimpleVertexShader.vertexshader").c_str();
	const GLchar * tempVShader = vShaderString.c_str();
	GLuint vertexShader = glCreateShader( GL_VERTEX_SHADER );
	glShaderSource(vertexShader, 1, & tempVShader, NULL);
	glCompileShader( vertexShader ); 
	std::fstream logs;
	logs.open( "logs.txt", ios::in | ios::out | ios::trunc );
	char  vsbuffer[512];
	glGetShaderInfoLog( vertexShader, 512, NULL, vsbuffer );
	logs << vsbuffer;
	//fragment shader loading
	const string fShaderString = loadShaderFile("SimpleFragmentShader.fragmentshader").c_str();
	const GLchar * tempFShader = fShaderString.c_str();
	GLuint fragmentShader = glCreateShader( GL_FRAGMENT_SHADER );
	glShaderSource(fragmentShader, 1, & tempFShader, NULL );
	glCompileShader(fragmentShader);
	char  fsbuffer[512];
	glGetShaderInfoLog( fragmentShader, 512, NULL, fsbuffer );
	logs << fsbuffer;
	if(glGetError() != 0)
	{
		logs << "sth errors";
		cout << "sth wrong" << endl;
	}
	logs.close();
	GLuint shaderProgram = glCreateProgram();
	glAttachShader( shaderProgram, vertexShader );
	glAttachShader( shaderProgram, fragmentShader);
	glBindFragDataLocation( shaderProgram, 0, "outColor" );
	glLinkProgram( shaderProgram );
	glUseProgram( shaderProgram );
	GLint posAttrib = glGetAttribLocation( shaderProgram, "position" );
	glEnableVertexAttribArray( posAttrib );
	glVertexAttribPointer( posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0 );
	while( glfwGetWindowParam( GLFW_WINDOW ) )
	{
		glDrawArrays( GL_TRIANGLES, 0, 3);
		glfwSwapBuffers();
	}
	glDeleteProgram( shaderProgram );
	glDeleteShader( vertexShader );
	glDeleteShader( fragmentShader );
	glDeleteBuffers(1,  & vbo );
	glDeleteVertexArrays(1, &vao );
	glfwTerminate();
	return 0;
}
BornToCode
BornToCode

Something is wrong exactly where. When you say something wrong is here, it does not help. Can you be a little bit more clear.

beans222
beans222

There's missing () after glGetError. As is it's not getting called (what you have there is a comparison of the function's address).

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Dark Engineer
Dark Engineer

It doesn't change anything. When i turn application on then debug error appears with Invalid allocation size: 4294967295 bytes

untitled.png

SimonForsman
SimonForsman
Since you are using shaders ... post them.
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The voices in my head may not be real, but they have some good ideas!
Dark Engineer
Dark Engineer

SimpleFragmentShader


#version 150

out vec4 outColor;

void main()
{
    outColor = vec4( 1.0, 1.0, 1.0, 1.0 );
}

SimpleVertexShader


#version 150

in vec2 position;

void main()
{
    gl_Position = vec4( position, 0.0, 1.0 );
}

and function for loading them


string loadShaderFile(const string fileName)
{
    
    ifstream shaderFile( fileName.c_str());

    //find the file size
    shaderFile.seekg(0, ios::end);
    std::streampos length = shaderFile.tellg();
    shaderFile.seekg(0, ios::beg);

    //read whole file into a vector
    vector<char> buffer(length);
    shaderFile.read(&buffer[0], length);

    //return the shader string
    return string( buffer.begin(), buffer.end());
}

I think something is wrong under 53 line but i'm begginer in OpenGL

Helo7777
Helo7777

Check that the functions you're using are returning valid data.


const GLchar * tempVShader = vShaderString.c_str();

Make sure "tempVShader" has a valid string.


char  vsbuffer[512];
glGetShaderInfoLog( vertexShader, 512, NULL, vsbuffer );
logs << vsbuffer;

Make sure "vsbuffer" has valid data and is NULL terminated.


const GLchar * tempFShader = fShaderString.c_str();

Check "tempFShader" is valid.



char  fsbuffer[512];
glGetShaderInfoLog( fragmentShader, 512, NULL, fsbuffer );
logs << fsbuffer;

Make sure "fsbuffer" has valid data and is NULL terminated.

Helo7777
Helo7777

And to be totally safe, logging should be used as follows, and after the call to glCompileShader()


GLint retParam;
glGetShaderiv(m_openGLID, GL_COMPILE_STATUS, &retParam);
if(retParam != GL_TRUE) 
{
	GLint errorMsgLen = 0;
	glGetShaderiv(m_openGLID, GL_INFO_LOG_LENGTH, &errorMsgLen);
	if (errorMsgLen > 0)
	{
		GLsizei charsWritten = 0;
		GLchar *errorMsg = new GLchar[errorMsgLen];
		glGetShaderInfoLog(m_openGLID, errorMsgLen, &charsWritten, errorMsg);

                /*Do something with errorMsg*/
	}
}
Dark Engineer
Dark Engineer
I have in console and logs that both shaders loaded successfully and program loaded successfully but still have this same error. Maybe i made something wrong with creating window.
Dark Engineer
Dark Engineer

Solved it just needed to change in loop GLFW_WINDOW to GLFW_OPENED

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