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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
use std::collections::HashMap;
use std::collections::hash_map::Entry::{Occupied, Vacant};
use geom::size::Size2D;
use layers::platform::surface::NativePaintingGraphicsContext;
use layers::layers::LayerBuffer;
use std::hash::{Hash, Hasher};
use std::mem;
/// This is a struct used to store buffers when they are not in use.
/// The paint task can quickly query for a particular size of buffer when it
/// needs it.
pub struct BufferMap {
/// A HashMap that stores the Buffers.
map: HashMap<BufferKey, BufferValue>,
/// The current amount of memory stored by the BufferMap's buffers.
mem: usize,
/// The maximum allowed memory. Unused buffers will be deleted
/// when this threshold is exceeded.
max_mem: usize,
/// A monotonically increasing counter to track how recently tile sizes were used.
counter: usize,
}
/// A key with which to store buffers. It is based on the size of the buffer.
#[derive(Eq, Copy, Clone)]
struct BufferKey([usize; 2]);
impl Hash for BufferKey {
fn hash<H: Hasher>(&self, state: &mut H) {
let BufferKey(ref bytes) = *self;
bytes.hash(state);
}
}
impl PartialEq for BufferKey {
fn eq(&self, other: &BufferKey) -> bool {
let BufferKey(s) = *self;
let BufferKey(o) = *other;
s[0] == o[0] && s[1] == o[1]
}
}
/// Create a key from a given size
impl BufferKey {
fn get(input: Size2D<usize>) -> BufferKey {
BufferKey([input.width, input.height])
}
}
/// A helper struct to keep track of buffers in the HashMap
struct BufferValue {
/// An array of buffers, all the same size
buffers: Vec<Box<LayerBuffer>>,
/// The counter when this size was last requested
last_action: usize,
}
impl BufferMap {
// Creates a new BufferMap with a given buffer limit.
pub fn new(max_mem: usize) -> BufferMap {
BufferMap {
map: HashMap::new(),
mem: 0,
max_mem: max_mem,
counter: 0,
}
}
/// Insert a new buffer into the map.
pub fn insert(&mut self, graphics_context: &NativePaintingGraphicsContext, new_buffer: Box<LayerBuffer>) {
let new_key = BufferKey::get(new_buffer.get_size_2d());
// If all our buffers are the same size and we're already at our
// memory limit, no need to store this new buffer; just let it drop.
if self.mem + new_buffer.get_mem() > self.max_mem && self.map.len() == 1 &&
self.map.contains_key(&new_key) {
new_buffer.destroy(graphics_context);
return;
}
self.mem += new_buffer.get_mem();
// use lazy insertion function to prevent unnecessary allocation
let counter = &self.counter;
match self.map.entry(new_key) {
Occupied(entry) => {
entry.into_mut().buffers.push(new_buffer);
}
Vacant(entry) => {
entry.insert(BufferValue {
buffers: vec!(new_buffer),
last_action: *counter,
});
}
}
let mut opt_key: Option<BufferKey> = None;
while self.mem > self.max_mem {
let old_key = match opt_key {
Some(key) => key,
None => {
match self.map.iter().min_by(|&(_, x)| x.last_action) {
Some((k, _)) => *k,
None => panic!("BufferMap: tried to delete with no elements in map"),
}
}
};
if {
let list = &mut self.map.get_mut(&old_key).unwrap().buffers;
let condemned_buffer = list.pop().take().unwrap();
self.mem -= condemned_buffer.get_mem();
condemned_buffer.destroy(graphics_context);
list.is_empty()
}
{ // then
self.map.remove(&old_key); // Don't store empty vectors!
opt_key = None;
} else {
opt_key = Some(old_key);
}
}
}
// Try to find a buffer for the given size.
pub fn find(&mut self, size: Size2D<usize>) -> Option<Box<LayerBuffer>> {
let mut flag = false; // True if key needs to be popped after retrieval.
let key = BufferKey::get(size);
let ret = match self.map.get_mut(&key) {
Some(ref mut buffer_val) => {
buffer_val.last_action = self.counter;
self.counter += 1;
let buffer = buffer_val.buffers.pop().take().unwrap();
self.mem -= buffer.get_mem();
if buffer_val.buffers.is_empty() {
flag = true;
}
Some(buffer)
}
None => None,
};
if flag {
self.map.remove(&key); // Don't store empty vectors!
}
ret
}
/// Destroys all buffers.
pub fn clear(&mut self, graphics_context: &NativePaintingGraphicsContext) {
let map = mem::replace(&mut self.map, HashMap::new());
for (_, value) in map.into_iter() {
for tile in value.buffers.into_iter() {
tile.destroy(graphics_context)
}
}
self.mem = 0
}
pub fn mem(&self) -> usize {
self.mem
}
}
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