/**
* A utility method to load vertex data into an OpenGL "vertex array object" (VAO) for efficient
* rendering. The VAO stores several "vertex buffer objects" (VBOs) that contain the vertex
* attribute data.
*
* @param data reference to the vertex data to be loaded into a VAO
*/
private void initArrayBuffer(GLVertexData data) {
// Make a vertex array object (VAO) for this vertex data
// and store a reference to it
GLVertexArrayObject vao = new GLVertexArrayObject(gl, data.getElements().size() + 1);
data.setVAO(vao);
// Bind (activate) the VAO for the vertex data in OpenGL.
// The subsequent OpenGL operations on VBOs will be recorded (stored)
// in the VAO.
vao.bind();
// Store all vertex attributes in vertex buffer objects (VBOs)
ListIterator<VertexData.VertexElement> itr = data.getElements().listIterator(0);
data.getVAO().rewindVBO();
while (itr.hasNext()) {
VertexData.VertexElement e = itr.next();
// Bind the vertex buffer object (VBO)
gl.glBindBuffer(GL3.GL_ARRAY_BUFFER, data.getVAO().getNextVBO());
// Upload vertex data
gl.glBufferData(
GL3.GL_ARRAY_BUFFER,
e.getData().length * 4,
FloatBuffer.wrap(e.getData()),
GL3.GL_DYNAMIC_DRAW);
}
// Bind the default vertex buffer objects
gl.glBindBuffer(GL3.GL_ARRAY_BUFFER, 0);
// Store the vertex data indices into the last vertex buffer
gl.glBindBuffer(GL3.GL_ELEMENT_ARRAY_BUFFER, data.getVAO().getNextVBO());
gl.glBufferData(
GL3.GL_ELEMENT_ARRAY_BUFFER,
data.getIndices().length * 4,
IntBuffer.wrap(data.getIndices()),
GL3.GL_DYNAMIC_DRAW);
// Bind the default vertex array object. This "deactivates" the VAO
// of the vertex data
gl.glBindVertexArray(0);
}
/**
* The main rendering method.
*
* @param renderItem the object that needs to be drawn
*/
private void draw(RenderItem renderItem) {
// Set the material of the shape to be rendered
setMaterial(renderItem.getShape().getMaterial());
// Get reference to the vertex data of the render item to be rendered
GLVertexData vertexData = (GLVertexData) renderItem.getShape().getVertexData();
// Check if the vertex data has been uploaded to OpenGL via a
// "vertex array object" (VAO). The VAO will store the vertex data
// in several "vertex buffer objects" (VBOs) on the GPU. We do this
// only once for performance reasons. Once the data is in the VBOs
// asscociated with a VAO, it is stored on the GPU and rendered more
// efficiently.
if (vertexData.getVAO() == null) {
initArrayBuffer(vertexData);
}
// Set modelview and projection matrices in shader (has to be done in
// every step, since they usually have changed)
setTransformation(renderItem.getT());
// Bind the VAO of this shape. This activates the VBOs that we
// associated with the VAO. We already loaded the vertex data into the
// VBOs on the GPU, so we do not have to send them again.
vertexData.getVAO().bind();
// Try to connect the vertex buffers to the corresponding variables
// in the current vertex shader.
// Note: This is not part of the vertex array object, because the active
// shader may have changed since the vertex array object was initialized.
// We need to make sure the vertex buffers are connected to the right
// variables in the shader
ListIterator<VertexData.VertexElement> itr = vertexData.getElements().listIterator(0);
vertexData.getVAO().rewindVBO();
while (itr.hasNext()) {
VertexData.VertexElement e = itr.next();
int dim = e.getNumberOfComponents();
// Bind the next vertex buffer object
gl.glBindBuffer(GL3.GL_ARRAY_BUFFER, vertexData.getVAO().getNextVBO());
// Tell OpenGL which "in" variable in the vertex shader corresponds
// to the current vertex buffer object.
// We use our own convention to name the variables, i.e.,
// "position", "normal", "color", "texcoord", or others if
// necessary.
int attribIndex = -1;
switch (e.getSemantic()) {
case POSITION:
attribIndex = gl.glGetAttribLocation(activeShaderID, "position");
break;
case NORMAL:
attribIndex = gl.glGetAttribLocation(activeShaderID, "normal");
break;
case COLOR:
attribIndex = gl.glGetAttribLocation(activeShaderID, "color");
break;
case TEXCOORD:
attribIndex = gl.glGetAttribLocation(activeShaderID, "texcoord");
break;
}
gl.glVertexAttribPointer(attribIndex, dim, GL3.GL_FLOAT, false, 0, 0);
gl.glEnableVertexAttribArray(attribIndex);
}
// Render the vertex buffer objects
gl.glDrawElements(
GL3.GL_TRIANGLES,
renderItem.getShape().getVertexData().getIndices().length,
GL3.GL_UNSIGNED_INT,
0);
// We are done with this shape, bind the default vertex array
gl.glBindVertexArray(0);
cleanMaterial(renderItem.getShape().getMaterial());
}