OpenGL - Problems getting even simple rendering to work with shaders - opengl

Question

I am trying to get my very simple shader working with my current OpenGL set up. I am using a shader manager and upon loading the shaders, all the output says they have loaded correctly.
Here is my data:
static const GLfloat g_vertex_buffer_data[] = {
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
0.0f, 1.0f, 0.0f,
};
Here is where i set up my buffer:
// This will identify our vertex buffer
GLuint vertexbuffer;
// Generate 1 buffer, put the resulting identifier in vertexbuffer
glGenBuffers(1, &vertexbuffer);
// The following commands will talk about our 'vertexbuffer' buffer
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
// Give our vertices to OpenGL.
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);
Here is my declaration of my shader using a tested and working shader loader:
Shader shader;
shader.loadFromFile(VERTEX_SHADER, resourcePath() + "tri.vert");
shader.loadFromFile(FRAGMENT_SHADER, resourcePath() + "tri.frag");
shader.createAndLinkProgram();
shader.use();
shader.addAttribute("position");
shader.unUse();
The attributes for this shader are then stored in a map. This is the rendering call:
shader.use();
glEnableVertexAttribArray(shader["position"]);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(
shader["position"], // attribute 0. No particular reason for 0, but must match the layout in the shader.
3, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);
// Draw the triangle !
glDrawArrays(GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle
glDisableVertexAttribArray(shader["position"]);
shader.unUse();
I then swap the buffers. I tried with an old GL_TRIANGLES fixed pipeline drawing and it worked fine.
Here is my vertex shader:
#version 330
layout(location = 0) in vec3 position;
void main()
{
gl_Position.xyz = position;
}
Here is my fragment shader:
out vec3 color;
main()
{
color = vec3(1,0,0);
}
It is supposed to simply draw a red triangle. When I draw using intermediate mode, it renders fine. I am running Xcode on Mac OSX 10.7.4.

Answer 1

gl_Position.xyz = position;
And what is the W coordinate? It's kind of important not to leave it undefined. If you want it to be 1.0, you need to set it to be that:
gl_Position = vec4(position, 1.0);

Answer 2

gl_Position must be provided with x,y,z,w coordinate.
In GLSL version above 1.50 u have to provide the matrix manipulation in the shader i.e u have to do ll the projection , model, view matrix using some math library like GLM http://glm.g-truc.net/
from the vertex data set the z coordinate is 0.0 which is co insiding with the center of the scene.prove some -ve value o the Z coordinate and check for the results.