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use std::{ mem, fmt };
use std::error::Error;
use version::Api;
use version::Version;
use context::CommandContext;
use backend::Facade;
use BufferExt;
use GlObject;
use ContextExt;
use CapabilitiesSource;
use TransformFeedbackSessionExt;
use buffer::{Buffer, BufferAnySlice};
use index::PrimitiveType;
use program::OutputPrimitives;
use program::Program;
use vertex::Vertex;
use gl;
/// Transform feedback allows you to obtain in a buffer the list of the vertices generated by
/// the vertex shader, geometry shader, or tessellation evaluation shader of your program. This
/// is usually used to cache the result in order to draw the vertices multiple times with multiple
/// different fragment shaders.
///
/// To use transform feedback, you must create a transform feedback session. A transform feedback
/// session mutably borrows the buffer where the data will be written. Each draw command submitted
/// with a session will continue to append data after the data written by the previous draw command.
/// You can only use the data when the session is destroyed.
///
/// # Notes
///
/// Here are a few things to note if you aren't familiar with transform feedback:
///
/// - The program you use must have transform feedback enabled, either with attributes in the
/// vertex shader's source code (for recent OpenGL versions only) or by indicating a list of
/// vertex attributes when building the program.
///
/// - A transform feedback session is bound to a specific program and buffer. You can't switch
/// them once the session has been created. An error is generated if you draw with a different
/// program than the one you created the session with.
///
/// - The transform feedback process doesn't necessarily fill the whole buffer. To retrieve the
/// number of vertices that are written to the buffer, use a query object (see the
/// `draw_parameters` module). It is however usually easy to determine in advance the number of
/// vertices that will be written based on the input data.
///
/// - The buffer will obtain either a list of points, a list of lines (two vertices), or a list of
/// triangles (three vertices). If you draw a triangle strip or a triangle fan for example,
/// individual triangles will be written to the buffer (meaning that some vertices will be
/// duplicated).
///
/// - You can use the same session multiple times in a row, in which case the data will continue
/// to be pushed in the buffer after the existing data. However you must always use the same type
/// of primitives and the same program.
///
/// # Example
///
/// ```no_run
/// # #[macro_use]
/// # extern crate glium;
/// # use glium::Surface;
/// # fn main() {
/// # let display: glium::Display = unsafe { std::mem::uninitialized() };
/// # let program: glium::Program = unsafe { std::mem::uninitialized() };
/// # let vb: glium::vertex::VertexBufferAny = unsafe { std::mem::uninitialized() };
/// # let ib: glium::index::IndexBuffer<u16> = unsafe { std::mem::uninitialized() };
/// #[derive(Copy, Clone, Debug, PartialEq)]
/// struct Vertex {
/// output_val: (f32, f32),
/// }
///
/// implement_vertex!(Vertex, output_val);
///
/// let mut out_buffer: glium::VertexBuffer<Vertex> = glium::VertexBuffer::empty(&display, 6).unwrap();
///
/// {
/// let session = glium::vertex::TransformFeedbackSession::new(&display, &program,
/// &mut out_buffer).unwrap();
///
/// let params = glium::DrawParameters {
/// transform_feedback: Some(&session),
/// .. Default::default()
/// };
///
/// display.draw().draw(&vb, &ib, &program, &uniform!{}, ¶ms).unwrap();
/// }
///
/// let result: Vec<Vertex> = out_buffer.read().unwrap();
/// println!("List of generated vertices: {:?}", result);
/// # }
/// ```
#[derive(Debug)]
pub struct TransformFeedbackSession<'a> {
buffer: BufferAnySlice<'a>,
program: &'a Program,
}
/// Error that can happen when creating a `TransformFeedbackSession`.
#[derive(Debug, Clone)]
pub enum TransformFeedbackSessionCreationError {
/// Transform feedback is not supported by the OpenGL implementation.
NotSupported,
/// The format of the output doesn't match what the program is expected to output.
WrongVertexFormat,
}
impl fmt::Display for TransformFeedbackSessionCreationError {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
write!(fmt, "{}", self.description())
}
}
impl Error for TransformFeedbackSessionCreationError {
fn description(&self) -> &str {
use self::TransformFeedbackSessionCreationError::*;
match *self {
NotSupported =>
"Transform feedback is not supported by the OpenGL implementation",
WrongVertexFormat =>
"The format of the output doesn't match what the program is expected to output",
}
}
}
/// Returns true if transform feedback is supported by the OpenGL implementation.
#[inline]
pub fn is_transform_feedback_supported<F>(facade: &F) -> bool where F: Facade {
let context = facade.get_context();
context.get_version() >= &Version(Api::Gl, 3, 0) ||
context.get_version() >= &Version(Api::GlEs, 3, 0) ||
context.get_extensions().gl_ext_transform_feedback
}
impl<'a> TransformFeedbackSession<'a> {
/// Builds a new transform feedback session.
///
/// TODO: this constructor should ultimately support passing multiple buffers of different
/// types
pub fn new<F, V>(facade: &F, program: &'a Program, buffer: &'a mut Buffer<[V]>)
-> Result<TransformFeedbackSession<'a>, TransformFeedbackSessionCreationError>
where F: Facade, V: Vertex + Copy + Send + 'static
{
if !is_transform_feedback_supported(facade) {
return Err(TransformFeedbackSessionCreationError::NotSupported);
}
if !program.transform_feedback_matches(&<V as Vertex>::build_bindings(),
mem::size_of::<V>())
{
return Err(TransformFeedbackSessionCreationError::WrongVertexFormat);
}
Ok(TransformFeedbackSession {
buffer: buffer.as_slice_any(),
program: program,
})
}
}
impl<'a> TransformFeedbackSessionExt for TransformFeedbackSession<'a> {
fn bind(&self, mut ctxt: &mut CommandContext, draw_primitives: PrimitiveType) {
// TODO: check that the state matches what is required
if ctxt.state.transform_feedback_enabled.is_some() {
unimplemented!();
}
// FIXME: use the memory barrier system
self.buffer.bind_to_transform_feedback(ctxt, 0);
unsafe {
let primitives = match (self.program.get_output_primitives(), draw_primitives) {
(Some(OutputPrimitives::Points), _) => gl::POINTS,
(Some(OutputPrimitives::Lines), _) => gl::LINES,
(Some(OutputPrimitives::Triangles), _) => gl::TRIANGLES,
(Some(OutputPrimitives::Quads), _) => panic!(), // TODO: return a proper error
(None, PrimitiveType::Points) => gl::POINTS,
(None, PrimitiveType::LinesList) => gl::LINES,
(None, PrimitiveType::LinesListAdjacency) => gl::LINES,
(None, PrimitiveType::LineStrip) => gl::LINES,
(None, PrimitiveType::LineStripAdjacency) => gl::LINES,
(None, PrimitiveType::LineLoop) => gl::LINES,
(None, PrimitiveType::TrianglesList) => gl::TRIANGLES,
(None, PrimitiveType::TrianglesListAdjacency) => gl::TRIANGLES,
(None, PrimitiveType::TriangleStrip) => gl::TRIANGLES,
(None, PrimitiveType::TriangleStripAdjacency) => gl::TRIANGLES,
(None, PrimitiveType::TriangleFan) => gl::TRIANGLES,
(None, PrimitiveType::Patches { .. }) => unreachable!(),
};
ctxt.gl.BeginTransformFeedback(primitives);
ctxt.state.transform_feedback_enabled = Some(primitives);
ctxt.state.transform_feedback_paused = false;
}
}
#[inline]
fn unbind(mut ctxt: &mut CommandContext) {
if ctxt.state.transform_feedback_enabled.is_none() {
return;
}
unsafe {
ctxt.gl.EndTransformFeedback();
ctxt.state.transform_feedback_enabled = None;
ctxt.state.transform_feedback_paused = false;
}
}
fn ensure_buffer_out_of_transform_feedback(mut ctxt: &mut CommandContext, buffer: gl::types::GLuint) {
if ctxt.state.transform_feedback_enabled.is_none() {
return;
}
let mut needs_unbind = false;
for elem in ctxt.state.indexed_transform_feedback_buffer_bindings.iter_mut() {
if elem.buffer == buffer {
needs_unbind = true;
break;
}
}
if needs_unbind {
TransformFeedbackSession::unbind(ctxt);
}
}
}
impl<'a> Drop for TransformFeedbackSession<'a> {
#[inline]
fn drop(&mut self) {
// Since the session can be mem::forget'ed, the code in buffer/alloc.rs ensures that the
// buffer isn't used by transform feedback.
// However we end the session now anyway.
let mut ctxt = self.buffer.get_context().make_current();
Self::ensure_buffer_out_of_transform_feedback(&mut ctxt, self.buffer.get_id());
}
}