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);