OPENGL: Square Class Using VBO

Question

So, I am trying to make a basic "Drawable" class that handles a lot of the drawing for me in the background and I want to use modern OpenGL (no begin and end statements). I keep just getting a blank screen when I run draw().

I have run the debugger and checked, my array is initialized properly with 3xFLOAT for position and 4xFLOAT for color. Any idea what is going wrong? I am very new to this library. My example tries to draw a red cube at (+-0.5, +-0.5, 0.0), so the indexData array is just { 0, 1, 2, 3 }.

#define DRAWABLE_VERTEX_DEPTH 3
#define SIZE_OF_VERTEX_ELEMENT sizeof(GLfloat)
#define VERTEX_SIZE (DRAWABLE_VERTEX_DEPTH * SIZE_OF_VERTEX_ELEMENT)
#define DRAWABLE_COLOR_DEPTH 4
#define SIZE_OF_COLOR_ELEMENT sizeof(GLfloat)
#define COLOR_SIZE (DRAWABLE_COLOR_DEPTH * SIZE_OF_COLOR_ELEMENT)
#define INDEX_SIZE sizeof(GLushort)
#define DRAWABLE_STRIDE (VERTEX_SIZE + COLOR_SIZE)

inline Drawable(/*Arguments omitted for brevity...*/)
    {
        //Standard initialization omitted....

        glGenBuffers(1, &vboID);
        glGenBuffers(1, &vioID);
        glGenVertexArrays(1, &vaoID);

        glBindBuffer(GL_ARRAY_BUFFER, vboID);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vioID);

        glBufferData(GL_ARRAY_BUFFER, (VERTEX_SIZE + COLOR_SIZE) * vertexCount, vertexData, drawType);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, INDEX_SIZE * indexCount, indexData, drawType);

        glEnableVertexAttribArray(0);
        glEnableVertexAttribArray(1);

        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

        //Generate Vertex Array

        glBindVertexArray(vaoID);
        glBindBuffer(GL_ARRAY_BUFFER, vboID);
        glEnableVertexAttribArray(0);
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(0, DRAWABLE_VERTEX_DEPTH, GL_FLOAT, GL_FALSE, DRAWABLE_STRIDE, 0);
        glVertexAttribPointer(1, DRAWABLE_COLOR_DEPTH, GL_FLOAT, GL_FALSE, DRAWABLE_STRIDE, (GLbyte*)VERTEX_SIZE);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vioID);
        glBindVertexArray(0);
    }

    inline void draw()
    {
        glBindVertexArray(vaoID);
        glDrawElements(drawMode, indexCount, GL_UNSIGNED_SHORT, NULL);
        glBindVertexArray(0);
    }

GLSL Vertex Shader:

#version 430\r\n

in layout(location=0) vec3 inPosition;
in layout(location=1) vec4 inColor;
out vec4 outVertexColor;

void main()
{
    gl_Position = vec4(inPosition, 1.0);
    outVertexColor = inColor;
}

GLSL Fragment Shader:

#version 430\r\n

in vec4 outVertexColor;
out vec4 outFragmentcolor;

void main()
{
    outFragmentcolor = outVertexColor;
}

You have to call glEnableClientState(GL_VERTEX_ARRAY); before calling glBindVertexArray(vaoID); and glDisableClientState(GL_VERTEX_ARRAY); after glBindVertexArray(0);. — ProXicT
Thx for the response! I just added that, but it seemed to have no effect. What exactly does that do? And do I need it in both places where I bind the Vertex Array? — guitar80
I just took a quick look in your code and found this missing. It basicly enables/disables the capability specified in the parameter. Try to put glEnableVertexAttribArray(0); glEnableVertexAttribArray(1); there instead. And don't forget to disable it again. — ProXicT
Still no luck... Just a blank screen. I wondered if it maybe had something to do with the fact that I have interleaved color and vertex information in my VBO. — guitar80
Are you using shaders? Your code is using generic vertex attributes, which can only be used with shaders. Also, there's a mismatch in the index types. You're using GLushort to calculate the size, but GL_UNSIGNED_INT as the argument to glDrawElements(). — Reto Koradi

Kornel Kisielewicz Kornel Kisielewicz · Accepted Answer · 2015-10-08T10:11:48

Apart from the issues mentioned in the comments, your index array is GLushort (unsigned 16 bit), while your draw call specifies GL_UNSIGNED_INT (unsigned 32 bit). Replace with GL_UNSIGNED_SHORT.

OPENGL: Square Class Using VBO

1 Answers