qt opengl coloring cube example-vbo edited

[saman_artorious]

To write a vbo sample I edited the qt opengl coloring cube example. What I did is to create a vao and two vbos for vertices and colors variables. Unfortunately, when program runs, it doesn't render anything. Attached file is the program, as I am only using Linux, you may not worry about any virus detections.
I would appreciate if you run this example on your system and try if you can make it give the desired output.

[wysota]

You are not linking the buffers to the shader program you are using anywhere. Are you sure this is just a modified version of an example?

[saman_artorious]

You are not linking the buffers to the shader program you are using anywhere.

I changed the coloring example and added vbo to it. I do not understand your statement. I already linked vertices and colors variables to vertex and color respectively in the shader program. I do not understand where I am doing wrong.
could get more into the details please.

[wysota]

I already linked vertices and colors variables to vertex and color respectively in the shader program.
Where exactly did you do that? Which file, which line?

[saman_artorious]

Please check the file
glwidget.cpp.
The linking of shader programs is happening inside
initializeGL()
Rendering and initialization(if not initialized)is done in the
paintGL() function.






if(!initialized)
{
GLuint vertexId = shaderProgram.attributeLocation("vertex");

GLuint colorId = shaderProgram.attributeLocation("color");

glGenVertexArrays(1, &VAO_ID);
glBindVertexArray(VAO_ID);

glBindBuffer(GL_ARRAY_BUFFER, VBO_ID[0]);
glVertexAttribPointer(vertexId, 3, GL_FLOAT, GL_FALSE, sizeof(vertices), 0);
glBufferData(GL_ARRAY_BUFFER, sizeof(QVector3D)*vertices.size(), vertices.constData(), GL_STATIC_DRAW);

glBindBuffer(GL_ARRAY_BUFFER, VBO_ID[1]);
glVertexAttribPointer(colorId, 3, GL_FLOAT, GL_FALSE, sizeof(colors), 0);
glBufferData(GL_ARRAY_BUFFER, sizeof(QVector3D)*colors.size(), colors.constData(), GL_STATIC_DRAW);

initialized = true;
}

[wysota]

Again, which line in your opinion binds the VBO to the shader? Because none of what you posted in this post does. This code only fills the buffer.

[saman_artorious]

Again, which line in your opinion binds the VBO to the shader? Because none of what you posted in this post does. This code only fills the buffer.

Here:


int vertexLocation = shaderProgram->attributeLocation("vertex");
shaderProgram->enableAttributeArray(vertexLocation);
int colorLocation = shaderProgram->attributeLocation("color");
shaderProgram->enableAttributeArray(colorLocation);

[wysota]

I think you forgot to read the docs for "enableAttributeArray". This only tells the shader to expect an array instead of a single value. It does not tell it what data to assign to this array. I already told you in the other thread a couple of days ago which function you need to use. Now RTFM for enableAttributeArray and read the other thread again.

[saman_artorious]

I added the two lines concerning setAttributeBuffer() to my code. However, it gives me segmentation fault when after glDrawArray() is called. Though it executes fine with

glDrawElements(GL_TRIANGLES, vertices.size(), GL_FLOAT, vertices.constData()); but does not render anything on the screen.



shaderProgram->setAttributeBuffer(vertexLocation, GL_FLOAT , 0, 3, 0);
shaderProgram->setAttributeBuffer(colorLocation , GL_FLOAT , 0, 1, 0);


whole render part:


if(!initialized)
{
GLuint vertexId = shaderProgram->attributeLocation("vertex");

GLuint colorId = shaderProgram->attributeLocation("color");

glGenBuffers(2, VBO_ID);
glGenVertexArrays(1, &VAO_ID);
glBindVertexArray(VAO_ID);

glBindBuffer(GL_ARRAY_BUFFER, VBO_ID[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(QVector3D)*vertices.size(), vertices.constData(), GL_STATIC_DRAW);
glVertexAttribPointer(vertexId, 3, GL_FLOAT, GL_FALSE, 0, 0);// param - 1 ->0
glEnableVertexAttribArray(vertexId);

glBindBuffer(GL_ARRAY_BUFFER, VBO_ID[1]);
glBufferData(GL_ARRAY_BUFFER, sizeof(float)*vertices.size(), colors, GL_DYNAMIC_DRAW);
glVertexAttribPointer(colorId, 1, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(colorId);

glBindBuffer(GL_ARRAY_BUFFER, 0);
}

glBindVertexArray(VAO_ID);

int vertexLocation = shaderProgram->attributeLocation("vertex");
int colorLocation = shaderProgram->attributeLocation("color");

shaderProgram->enableAttributeArray(vertexLocation);
shaderProgram->enableAttributeArray(colorLocation);

shaderProgram->setAttributeBuffer(vertexLocation, GL_FLOAT , 0, 3, 0);
shaderProgram->setAttributeBuffer(colorLocation , GL_FLOAT , 0, 1, 0);

glEnable (GL_BLEND);
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glDrawArrays(GL_TRIANGLES, 0, numVerts);


could you please run this code on your system, I don't know exactly what I am missing. Although, I added setArrtibuteBuffers.

[wysota]

Make sure you are setting up the buffers correctly. I would also advise to use Qt classes for VBO manipulation.

[saman_artorious]

Make sure you are setting up the buffers correctly. I would also advise to use Qt classes for VBO manipulation.

Thanks for your guidance. I solved the problem. The correct code for what I aimed for is:


if(!initialized)
{
GLuint vertexId = shaderProgram->attributeLocation("vertex");
GLuint colorId = shaderProgram->attributeLocation("color");

glGenBuffers(2, VBO_ID);

glGenVertexArrays(1, &VAO_ID);
glBindVertexArray(VAO_ID);

glBindBuffer(GL_ARRAY_BUFFER, VBO_ID[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(QVector3D)*verticesSize, vertices.constData(), GL_STATIC_DRAW);
glVertexAttribPointer(vertexId, 3, GL_FLOAT, GL_FALSE, 0, 0);// param - 1 ->0
glEnableVertexAttribArray(vertexId);

glBindBuffer(GL_ARRAY_BUFFER, VBO_ID[1]);
glBufferData(GL_ARRAY_BUFFER, sizeof(float)*verticesSize, colors, GL_STATIC_DRAW);
glVertexAttribPointer(colorId, 1, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(colorId);

glBindBuffer(GL_ARRAY_BUFFER, 0);

vertices.clear();

free(colors);

initialized = true;
}

glBindVertexArray(VAO_ID);

int vertexLocation = shaderProgram->attributeLocation("vertex");
int colorLocation = shaderProgram->attributeLocation("color");

shaderProgram->enableAttributeArray(vertexLocation);
shaderProgram->enableAttributeArray(colorLocation);

glEnableClientState(GL_VERTEX_ARRAY);

glEnable (GL_BLEND);
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glDrawArrays(GL_TRIANGLES, 0, 6*numVerts);

glFlush();

glBindVertexArray(0);

glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);