Develop Reference

How do I use Vertex Array Objects in OpenGL

I'm using lwjgl 3 as a Java wrapper to OpenGL, and I'm trying to figure out how to render things with Vertex Array Objects. I have not been able to find any examples online that show how to use a VAO that has both shader attributes and uses the element array buffer.
According to this vao tutorial, I need to do something like this:
// Create a new Vertex Array Object in memory and select it (bind)
// A VAO can have up to 16 attributes (VBO's) assigned to it by default
vaoId = GL30.glGenVertexArrays();
GL30.glBindVertexArray(vaoId);
// Create a new Vertex Buffer Object in memory and select it (bind)
// A VBO is a collection of Vectors which in this case resemble the location of each vertex.
vboId = GL15.glGenBuffers();
GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vboId);
GL15.glBufferData(GL15.GL_ARRAY_BUFFER, verticesBuffer, GL15.GL_STATIC_DRAW);
// Put the VBO in the attributes list at index 0
GL20.glVertexAttribPointer(0, 3, GL11.GL_FLOAT, false, 0, 0);
// Deselect (bind to 0) the VBO
GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0);
// Deselect (bind to 0) the VAO
GL30.glBindVertexArray(0);
However, I don't understand how to adapt this tutorial to my project, because I am using glVertexAttribPointer to deal with fields in the shader. These fields have id's that are assigned to them when the shader is compiled. In the above example, they seem to be able to use the default field 0. However, I checked, for me posAttrib is in field 0.
How should I associate a VBO with my VAO?
private int createVao(int shaderProgramId, FloatBuffer vertices, IntBuffer order) {
int floatSize = 4;
int stride = 7 * floatSize;
int vaoId = glGenVertexArrays();
glBindVertexArray(vaoId);
int vboId = glGenBuffers();
glBindBuffer(GL_ARRAY_BUFFER, vboId);
glBufferData(GL_ARRAY_BUFFER, vertices, GL_STATIC_DRAW);
int eboId = glGenBuffers();
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, eboId);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, order, GL_STATIC_DRAW);
int posAttrib = shaderProgramService.getAttribute(shaderProgramId, "position");
glEnableVertexAttribArray(posAttrib);
glVertexAttribPointer(posAttrib, 2, GL_FLOAT, false, stride, 0);
int colAttrib = shaderProgramService.getAttribute(shaderProgramId, "color");
glEnableVertexAttribArray(colAttrib);
glVertexAttribPointer(colAttrib, 3, GL_FLOAT, false, stride, 2 * floatSize);
int texAttrib = shaderProgramService.getAttribute(shaderProgramId, "texcoord");
glEnableVertexAttribArray(texAttrib);
glVertexAttribPointer(texAttrib, 2, GL_FLOAT, false, stride, 5 * floatSize);
// glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); <==== Removed
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
return vaoId;
}
EDIT: Thanks #RetoKoradi, getting rid of the glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); call improved things. The scene flashed onscreen, but I got a seg-fault on the second frame. After some debugging, the issue was with another object I was trying to render that was not yet using VAO's. I was making calls like this to render the object:
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, texturedPoints.getEboId());
glBindBuffer(GL_ARRAY_BUFFER, texturedPoints.getVboId());
glBindTexture(GL_TEXTURE_2D, texturedPoints.getTextureId());
specifyVertexAttributes();
int count = texturedPoints.getCount();
glDrawElements(GL_TRIANGLES, count, GL_UNSIGNED_INT, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
Somehow that interfered with subsequent VAO rendering calls that looked like this:
glBindVertexArray(texturedPoints.getVaoId());
glBindTexture(GL_TEXTURE_2D, texturedPoints.getTextureId());
glDrawElements(GL_TRIANGLES, texturedPoints.getCount(), GL_UNSIGNED_INT, 0);
The glDrawElements call would seg-fault the second time that the main loop went around and called it. After moving everything over to VAO's the problems have gone away.

glDrawElements with VBO

I want to render my vertices with the order defined by an Index Buffer.
If I use
glDrawElements(int mode, ByteBuffer indices);
everything works fine, but if I want to upload this data to GL_ELEMENT_ARRAY_BUFFER I get a black screen and the glError 1281.
This is my code:
public void buildBuffer() {
//generate VBOs
FloatBuffer buffer = BufferUtils.createFloatBuffer(this.model.getVertexData().size() * 3);
for (float[] f : this.model.getVertexData()) {
buffer.put(f);
}
buffer.flip();
glBindBuffer(GL_ARRAY_BUFFER, this.vVBO);
glBufferData(GL_ARRAY_BUFFER, buffer, GL_STATIC_DRAW);
ByteBuffer ibuffer = BufferUtils.createByteBuffer(3);
ibuffer.put((byte) 1);
ibuffer.put((byte) 2);
ibuffer.put((byte) 3);
ibuffer.flip();
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this.iVBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, ibuffer, GL_STATIC_DRAW);
glBindVertexArray(this.VAO);
glBindBuffer(GL_ARRAY_BUFFER, this.vVBO);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);
glBindVertexArray(0);
}
public void draw() {
this.shader.use();
glBindVertexArray(this.VAO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this.iVBO);
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_BYTE, 0);
glBindVertexArray(0);
Shader.NONE.use();
}

It's hard to tell, but i'll try to take a shot at it.
You never actually create the VAO, before binding the vertex array, you have to set the VAO to vaoID = GL30.glGenVertexArrays();.
When you put the array of data into the FloatBuffer, you don't need a for loop. It's as simple as buffer.put(vertices);.

If not GL_QUADS, then how?

I'm developing a simple 2D game in Java using the LWJGL wrapper for OpenGL.
For the rendering method, I use VBOs. It seems very good and faster the the other rendering methods.I was reading some articles and was seeking for some questions here on StackOverflow and I discovered that using 2 triangles is better than using one quad, since modern GPUs show only triangles (And it'll be a waste to let the GPU translate that quad into triangles).
The only way I know is creating 2 buffers for storing the vertex data and the texture coordinates data. and that's for a quad, this is how I do it:
int vertexID; //Holding the GL buffer ID for the Vertex
int texCoordsID; //Holding the GL buffer ID for the texture coords
void init(){
//BufferUtils is a Utility class provided by the SlickUtil library, I use it for creating buffers.
//Create float buffer for storing vertex data
FloatBuffer vertexBuffer = BufferUtils.createFloatBuffer(4 * 2);
//Put vertex data inside the buffer
vertexBuffer.put(new float[]{
0, 0,
100, 0,
100, 100,
0, 100
});
//Rewind the buffer
vertexBuffer.rewind();
FloatBuffer texCoordsBuffer = BufferUtils.createFloatBuffer(4 * 2);
texCoordsBuffer.put(new float[]{
0, 0,
1, 0,
1, 1,
0, 1
});
texCoordsBuffer.rewind();
vertexID = glGenBuffers();
glBindBuffer(GL_ARRAY_BUFFER, vertexID);
glBufferData(GL_ARRAY_BUFFER, vertexBuffer, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
texCoordsID = glGenBuffers();
glBindBuffer(GL_ARRAY_BUFFER, texCoordsID);
glBufferData(GL_ARRAY_BUFFER, texCoordsBuffer, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
void render(){
glBindTexture(GL_TEXTURE_2D, texture.id); //Not so important.
glBindBuffer(GL_ARRAY_BUFFER, vertexID);
glVertexPointer(2, GL_FLOAT, 0, 0);
glBindBuffer(GL_ARRAY_BUFFER, texCoordsID);
glTexCoordPointer(2, GL_FLOAT, 0, 0);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glDrawArrays(GL_QUADS, 0, 4);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
}
Now my main question is, how can you split it into 2 triangles instead of 1 quad?
And a side question: does it really matter for a 2D game? does it make a slight change?

Just change
glDrawArrays(GL_QUADS, 0, 4);
to
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
and add a slightly different vertex buffer
vertexBuffer.put(new float[]{
1.0, 1.0
-1.0, 1.0
1.0,-1.0
-1.0,-1.0
});
This represents two triangles, two 'points' are the same, so we have only four 'points'.
Just like:
x3__x4
| \ |
| \ |
x1__x2

Modern GLSL basics

I'm trying to learn the modern GLSL but i cant even display my a cube...
This is how i create VBO:
glBindBuffer(GL_ARRAY_BUFFER, vboVertexHandle);
glBufferData(GL_ARRAY_BUFFER, vertexData, GL_STATIC_DRAW);
glVertexPointer(3, GL_FLOAT, 0, 0L);
glBindBuffer(GL_ARRAY_BUFFER, vboNormalHandle);
glBufferData(GL_ARRAY_BUFFER, normalData, GL_STATIC_DRAW);
glNormalPointer(GL_FLOAT, 0, 0L);
glBindBuffer(GL_ARRAY_BUFFER, vboTextureHandle);
glBufferData(GL_ARRAY_BUFFER, textureData, GL_STATIC_DRAW);
glTexCoordPointer(2, GL_FLOAT, 0, 0L);
glBindBuffer(GL_ARRAY_BUFFER, 0);
this is how i render vbo:
glLoadIdentity();
glPushAttrib(GL_TRANSFORM_BIT);
glMatrixMode(GL_MODELVIEW);
glTranslatef(0f, 0f, camera.zoom);
glRotatef(camera.rotation.x, 1, 0, 0);
glRotatef(camera.rotation.y, 0, 1, 0);
glRotatef(camera.rotation.z, 0, 0, 1);
glTranslatef(camera.position.x, camera.position.y, camera.position.z);
glPopAttrib();
texture.bind();
glBindBuffer(GL_ARRAY_BUFFER, vboVertexHandle);
glVertexPointer(3, GL_FLOAT, 0, 0L);
glBindBuffer(GL_ARRAY_BUFFER, vboNormalHandle);
glNormalPointer(GL_FLOAT, 0, 0L);
glBindBuffer(GL_ARRAY_BUFFER, vboTextureHandle);
glTexCoordPointer(2, GL_FLOAT, 0, 0L);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glMaterialf(GL_FRONT, GL_SHININESS, 10f);
glDrawArrays(GL_TRIANGLES, 0, triangles.size() * 3);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glBindBuffer(GL_ARRAY_BUFFER, 0);
TextureImpl.bindNone();
if i dont use any shader programs or use something in the old glsl 120 everything renders fine, but when i use this program which should display my cube as i think, i get a black screen...
Vertex shader program:
#version 330
layout (std140) uniform Matrices {
mat4 pvm;
} ;
in vec4 position;
out vec4 color;
void main()
{
gl_Position = pvm * position ;
}
Fragment shader program:
#version 330
out vec4 outputF;
void main()
{
outputF = vec4(1.0, 0.0, 0.0, 1.0);
}
What do i do wrong? Where can i find out how to do this basic stuff with the modern glsl?

What we have here is a failure to communicate.
Consider this:
glVertexPointer(3, GL_FLOAT, 0, 0L);
OK. You're telling OpenGL that the position data is provided by some buffer object and that it has 3 floats per vertex. OK, fine.
How does OpenGL know that this position data is supposed to go to position in the vertex shader?
Answer: it doesn't.
glVertexPointer is a function that has been removed from GL 3.1+. It doesn't feed data to arbitrary vertex shader inputs; it feeds data to the removed vertex shader input gl_Vertex. This is hard-coded.
You should be using generic vertex attributes, generally through glVertexAttribPointer and glEnableVertexAttribArray. You should also be using VAOs.
Similarly, there is no way for OpenGL to know that you want it's removed matrix functions to feed data to the uniform pvm. Indeed, this is much worse, because you put that in a uniform block. The data for a uniform block is supposed to come from a user-provided buffer object. Which you did not provide, and which OpenGL won't magically provide for you.
In short, you can't mix old-style OpenGL code with modern-style GLSL. You can use old-style GLSL (using gl_Vertex and gl_ModelViewProjectionMatrix), but then you're not using modern-style GLSL.

VBO with texture in LWJGL

How do I attach a texture to a VBO?
I had it working with a colorBuffer and now i want to implement a texture.
This is my draw method:
Color.white.bind();
glBindTexture(GL_TEXTURE_2D, texture.getTextureID());
glBindBuffer(GL_ARRAY_BUFFER, vboVertexHandle);
glBufferData(GL_ARRAY_BUFFER, vertexData, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ARRAY_BUFFER, vboVertexHandle);
glBufferData(GL_ARRAY_BUFFER, textureData, GL_STATIC_DRAW);
glVertexPointer(vertexSize, GL_FLOAT, 0, 0L);
glEnableClientState(GL_VERTEX_ARRAY);
glTexCoordPointer(3, GL_FLOAT, 0, 0);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glDrawArrays(GL_QUADS, 0, amountOfVertices);
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
That doesn't display anything at all. the texture is correctly laoded and I got it working with the immediate mode.
What do I have to do to make it work with VBOs ?

Looks like the VBO for the texture coordinates is not bound while setting the texCoordPointer. Changing the order of your commands should work. Also you are overriding the vertex with your texCoord data in your single VBO. Easiest solutions would be to have two separate VBOs for each.
glBindTexture(GL_TEXTURE_2D, texture.getTextureID());
// vertices
glBindBuffer(GL_ARRAY_BUFFER, vboVertexHandle);
glBufferData(GL_ARRAY_BUFFER, vertexData, GL_STATIC_DRAW);
glVertexPointer(vertexSize, GL_FLOAT, 0, 0L);
// texCoords
glBindBuffer(GL_ARRAY_BUFFER, vboTexCoordHandle);
glBufferData(GL_ARRAY_BUFFER, textureData, GL_STATIC_DRAW);
glTexCoordPointer(3, GL_FLOAT, 0, 0);
// unbind VBO
glBindBuffer(GL_ARRAY_BUFFER, 0);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glDrawArrays(GL_QUADS, 0, amountOfVertices);
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
Note: usually you don't want to create new VBOs each frame by calling glBufferData more than once per VBO.