How do I pass vertex and color positions to OpenGL shaders?
- by smoth190
I've been trying to get this to work for the past two days, telling myself I wouldn't ask for help. I think you can see where that got me...
I thought I'd try my hand at a little OpenGL, because DirectX is complex and depressing. I picked OpenGL 3.x, because even with my OpenGL 4 graphics card, all my friends don't have that, and I like to let them use my programs. There aren't really any great tutorials for OpenGL 3, most are just "type this and this will happen--the end".
I'm trying to just draw a simple triangle, and so far, all I have is a blank screen with my clear color (when I set the draw type to GL_POINTS I just get a black dot). I have no idea what the problem is, so I'll just slap down the code:
Here is the function that creates the triangle:
void CEntityRenderable::CreateBuffers()
{
m_vertices = new Vertex3D[3];
m_vertexCount = 3;
m_vertices[0].x = -1.0f;
m_vertices[0].y = -1.0f;
m_vertices[0].z = -5.0f;
m_vertices[0].r = 1.0f;
m_vertices[0].g = 0.0f;
m_vertices[0].b = 0.0f;
m_vertices[0].a = 1.0f;
m_vertices[1].x = 1.0f;
m_vertices[1].y = -1.0f;
m_vertices[1].z = -5.0f;
m_vertices[1].r = 1.0f;
m_vertices[1].g = 0.0f;
m_vertices[1].b = 0.0f;
m_vertices[1].a = 1.0f;
m_vertices[2].x = 0.0f;
m_vertices[2].y = 1.0f;
m_vertices[2].z = -5.0f;
m_vertices[2].r = 1.0f;
m_vertices[2].g = 0.0f;
m_vertices[2].b = 0.0f;
m_vertices[2].a = 1.0f;
//Create the VAO
glGenVertexArrays(1, &m_vaoID);
//Bind the VAO
glBindVertexArray(m_vaoID);
//Create a vertex buffer
glGenBuffers(1, &m_vboID);
//Bind the buffer
glBindBuffer(GL_ARRAY_BUFFER, m_vboID);
//Set the buffers data
glBufferData(GL_ARRAY_BUFFER, sizeof(m_vertices), m_vertices, GL_STATIC_DRAW);
//Set its usage
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex3D), 0);
glVertexAttribPointer(1, 4, GL_FLOAT, GL_TRUE, sizeof(Vertex3D), (void*)(3*sizeof(float)));
//Enable
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
//Check for errors
if(glGetError() != GL_NO_ERROR)
{
Error("Failed to create VBO: %s", gluErrorString(glGetError()));
}
//Unbind...
glBindVertexArray(0);
}
The Vertex3D struct is as such...
struct Vertex3D
{
Vertex3D() : x(0), y(0), z(0), r(0), g(0), b(0), a(1) {}
float x, y, z;
float r, g, b, a;
};
And finally the render function:
void CEntityRenderable::RenderEntity()
{
//Render...
glBindVertexArray(m_vaoID);
//Use our attribs
glDrawArrays(GL_POINTS, 0, m_vertexCount);
glBindVertexArray(0); //unbind
OnRender();
}
(And yes, I am binding and unbinding the shader. That is just in a different place)
I think my problem is that I haven't fully wrapped my mind around this whole VertexAttribArray thing (the only thing I like better in DirectX was input layouts D:).
This is my vertex shader:
#version 330
//Matrices
uniform mat4 projectionMatrix;
uniform mat4 viewMatrix;
uniform mat4 modelMatrix;
//In values
layout(location = 0) in vec3 position;
layout(location = 1) in vec3 color;
//Out values
out vec3 frag_color;
//Main shader
void main(void)
{
//Position in world
gl_Position = vec4(position, 1.0);
//gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4(in_Position, 1.0);
//No color changes
frag_color = color;
}
As you can see, I've disable the matrices, because that just makes debugging this thing so much harder. I tried to debug using glslDevil, but my program just crashes right before the shaders are created... so I gave up with that. This is my first shot at OpenGL since the good old days of LWJGL, but that was when I didn't even know what a shader was. Thanks for your help :)
