PDF functions and mesh shadings: charge retained values, refuse short tables, bound lattice rows and raster work (#2972)

* PDF functions and mesh shadings: charge retained values, refuse short tables, bound lattice rows and raster work

Depth-limit fallbacks were not charged to the function node budget; cached
copies of a function deep-copied its coefficient and program vectors while
only its nodes were charged; sampled functions made up missing samples as
zeros; calculator programs had no size limit; a lattice row was filled
before any limit applied; and overlapping mesh triangles each scanned their
whole bounding box.

The node is charged before the depth check; coefficients, bounds, encode
arrays and calculator operators are charged (eight to a node) so cached
copies carry their cost; a sampled function shorter than its table is
unsupported; calculator programs hold at most 4,096 operators; lattice rows
past the triangle limit are refused and vertices stop at it; and triangle
bounding boxes share a budget of 64 passes over the raster.

* address review: bound calculator token count while parsing

* address review: count skipped calculator tokens toward MAX_CALC_OPS

* address review: skip arrays and dictionaries in a calculator program without building them

* address review: scalar tokens in a skipped compound are passed over without building them
This commit is contained in:
Dylan M. Taylor
2026-11-11 15:12:55 -05:00
committed by GitHub
parent 6c1391d4de
commit 4ba6ff32b8
5 changed files with 277 additions and 27 deletions
+122 -26
View File
@@ -215,19 +215,44 @@ pub enum PsOp {
Proc(Vec<PsOp>),
}
fn ps_parse(lx: &mut crate::object::Lexer, depth: usize) -> Vec<PsOp> {
/// Parse a procedure. `ops` counts the tokens read (those skipped as unsupported included); past
/// [`MAX_CALC_OPS`] the rest is not read, so an oversized program is never fully scanned or built
/// (the caller rejects it when `ops` ends past the cap).
fn ps_parse(lx: &mut crate::object::Lexer, depth: usize, ops: &mut usize) -> Vec<PsOp> {
let mut out = vec![];
while let Some(o) = lx.next() {
match o {
Obj::Num(n) => out.push(PsOp::Num(n)),
Obj::Bool(b) => out.push(PsOp::Num(if b { 1.0 } else { 0.0 })),
Obj::Op(op) if op == "{" && depth < 32 => out.push(PsOp::Proc(ps_parse(lx, depth + 1))),
// Nested too deep: skip the procedure's opening brace (never push it as an operator).
Obj::Op(op) if op == "{" => {}
Obj::Op(op) if op == "}" => return out,
Obj::Op(op) => out.push(PsOp::Op(op)),
_ => {}
loop {
// A calculator holds no arrays or dictionaries: one is skipped as a single token without
// being built (the lexer would allocate every element before this counted it).
if lx.at_compound() {
if *ops > MAX_CALC_OPS {
break;
}
lx.skip_compound();
*ops += 1;
continue;
}
let Some(o) = lx.next() else { break };
if *ops > MAX_CALC_OPS {
break;
}
let op = match o {
Obj::Num(n) => PsOp::Num(n),
Obj::Bool(b) => PsOp::Num(if b { 1.0 } else { 0.0 }),
Obj::Op(op) if op == "{" && depth < 32 => PsOp::Proc(ps_parse(lx, depth + 1, ops)),
// Nested too deep: skip the procedure's opening brace (never push it as an operator).
Obj::Op(op) if op == "{" => {
*ops += 1;
continue;
}
Obj::Op(op) if op == "}" => return out,
Obj::Op(op) => PsOp::Op(op),
_ => {
*ops += 1;
continue;
}
};
*ops += 1;
out.push(op);
}
out
}
@@ -243,6 +268,15 @@ fn ps_push(st: &mut Vec<f64>, v: f64) {
}
}
/// The most operators and operands a calculator program may hold (nested procedures included).
/// It has no loops, so this bounds what one evaluation runs; real programs hold a few dozen.
const MAX_CALC_OPS: usize = 4096;
/// The operators and operands in `code`, nested procedures included.
fn ps_len(code: &[PsOp]) -> usize {
code.iter().map(|op| if let PsOp::Proc(p) = op { 1 + ps_len(p) } else { 1 }).sum()
}
fn ps_run(code: &[PsOp], st: &mut Vec<f64>, depth: usize) {
if depth > 32 {
return;
@@ -431,6 +465,12 @@ impl Budget {
Budget { nodes: MAX_NODES, samples: MAX_SAMPLES, overrun: false }
}
/// Charge `n` retained values (coefficients, bounds, program operators) as nodes, eight to a
/// node, so a cached copy of a function is charged for what it holds, not just its node.
fn take_values(&mut self, n: usize) -> bool {
self.take_nodes(n.div_ceil(8))
}
/// Charge `n` nodes; `false` (and the read is abandoned) once the cap is passed.
fn take_nodes(&mut self, n: usize) -> bool {
match self.nodes.checked_sub(n) {
@@ -484,7 +524,8 @@ impl Func {
/// [`Func::read`] nested `depth` levels deep, charging `budget`: unsupported past [`MAX_DEPTH`]
/// or once the budget is spent.
fn read_at(file: &File, o: &Obj, depth: usize, budget: &mut Budget) -> Func {
if depth >= MAX_DEPTH || !budget.take_nodes(1) {
// Charged first: the fallback past the depth limit is a node a copy keeps too.
if !budget.take_nodes(1) || depth >= MAX_DEPTH {
return Func::Unsupported;
}
let o = file.resolve(o);
@@ -499,12 +540,14 @@ impl Func {
let dom = file.get(d, "Domain").map(|x| file.nums(x)).unwrap_or_default();
let domain = [dom.first().copied().unwrap_or(0.0), dom.get(1).copied().unwrap_or(1.0)];
match file.get_num(d, "FunctionType").unwrap_or(-1.0) as i32 {
2 => Func::Exp {
domain,
c0: file.get(d, "C0").map(|x| file.nums(x)).unwrap_or_else(|| vec![0.0]),
c1: file.get(d, "C1").map(|x| file.nums(x)).unwrap_or_else(|| vec![1.0]),
n: file.get_num(d, "N").unwrap_or(1.0),
},
2 => {
let c0 = file.get(d, "C0").map(|x| file.nums(x)).unwrap_or_else(|| vec![0.0]);
let c1 = file.get(d, "C1").map(|x| file.nums(x)).unwrap_or_else(|| vec![1.0]);
if !budget.take_values(c0.len() + c1.len()) {
return Func::Unsupported;
}
Func::Exp { domain, c0, c1, n: file.get_num(d, "N").unwrap_or(1.0) }
}
3 => {
// A stitching function's pieces: no element cap (a repeating gradient lists one
// piece once per repeat); the budget bounds the total work.
@@ -513,12 +556,12 @@ impl Func {
None => Some(vec![]),
};
let Some(funcs) = funcs else { return Func::Unsupported };
Func::Stitch {
domain,
funcs,
bounds: file.get(d, "Bounds").map(|x| file.nums(x)).unwrap_or_default(),
encode: file.get(d, "Encode").map(|x| file.nums(x)).unwrap_or_default(),
let bounds = file.get(d, "Bounds").map(|x| file.nums(x)).unwrap_or_default();
let encode = file.get(d, "Encode").map(|x| file.nums(x)).unwrap_or_default();
if !budget.take_values(bounds.len() + encode.len()) {
return Func::Unsupported;
}
Func::Stitch { domain, funcs, bounds, encode }
}
0 => {
let Obj::Stream(sd, raw) = o else { return Func::Unsupported };
@@ -537,6 +580,10 @@ impl Func {
if !budget.take_samples(count) {
return Func::Unsupported;
}
// The stream must hold the table: missing bytes are not made up as zeros.
if count.checked_mul(bps).is_none_or(|bits| bits.div_ceil(8) > data.len()) {
return Func::Unsupported;
}
let enc = file.get(d, "Encode").map(|x| file.nums(x)).unwrap_or_default();
let encode = [enc.first().copied().unwrap_or(0.0), enc.get(1).copied().unwrap_or(size as f64 - 1.0)];
let decode = file.get(d, "Decode").map(|x| file.nums(x)).filter(|v| v.len() >= outputs * 2).unwrap_or_else(|| range.clone());
@@ -567,10 +614,15 @@ impl Func {
let Some(data) = decode_stream(file, sd, raw) else { return Func::Unsupported };
let mut lx = crate::object::Lexer::new(&data, 0);
// The program is one procedure: `{ … }`.
let code = match ps_parse(&mut lx, 0).into_iter().next() {
let mut scanned = 0;
let code = match ps_parse(&mut lx, 0, &mut scanned).into_iter().next() {
Some(PsOp::Proc(p)) => p,
_ => return Func::Unsupported,
};
let ops = ps_len(&code);
if scanned > MAX_CALC_OPS || ops > MAX_CALC_OPS || !budget.take_values(ops) {
return Func::Unsupported;
}
Func::Calc { domain: dom, range: file.get(d, "Range").map(|x| file.nums(x)).unwrap_or_default(), code }
}
_ => Func::Unsupported,
@@ -756,12 +808,56 @@ mod tests {
assert_eq!(sample_count(1 << 22, usize::MAX / (1 << 22) + 1), None);
}
#[test]
fn oversized_calculator_program_is_cut_short() {
let src = format!("{{ {}}}", "1 ".repeat(MAX_CALC_OPS + 10));
let mut lx = crate::object::Lexer::new(src.as_bytes(), 0);
let Some(PsOp::Proc(code)) = ps_parse(&mut lx, 0, &mut 0).into_iter().next() else { panic!() };
assert_eq!(ps_len(&code), MAX_CALC_OPS + 1);
}
#[test]
fn arrays_and_dictionaries_in_a_calculator_are_skipped_whole() {
// Strings with brackets, nested arrays and a dictionary are one skipped token each; the
// operators around them still parse.
let src = b"{ 1 [ (a]b) [1 2] << /K [3 4] /S (>>) >> 5 ] 2 add << /A 1 >> mul }";
let mut lx = crate::object::Lexer::new(src, 0);
let Some(PsOp::Proc(code)) = ps_parse(&mut lx, 0, &mut 0).into_iter().next() else { panic!() };
assert_eq!(code, vec![PsOp::Num(1.0), PsOp::Num(2.0), PsOp::Op("add".into()), PsOp::Op("mul".into())]);
// A huge array is skipped once the cap is passed, not read to its end.
let src = format!("{{ [ {}] 1 }}", "0 ".repeat(MAX_CALC_OPS * 100));
let mut lx = crate::object::Lexer::new(src.as_bytes(), 0);
let mut scanned = 0;
let Some(PsOp::Proc(code)) = ps_parse(&mut lx, 0, &mut scanned).into_iter().next() else { panic!() };
assert_eq!(code, vec![PsOp::Num(1.0)]);
// A large string inside a skipped array is passed over, not decoded: escapes, nested
// parentheses, a hexadecimal string and names all end where the lexer would end them.
let big = format!("{{ [ ({}) <{}> /{} (a\\)b(c)) 7 ] 1 }}", "x".repeat(1 << 20), "ab".repeat(1 << 19), "N".repeat(1 << 10));
let mut lx = crate::object::Lexer::new(big.as_bytes(), 0);
let Some(PsOp::Proc(code)) = ps_parse(&mut lx, 0, &mut 0).into_iter().next() else { panic!() };
assert_eq!(code, vec![PsOp::Num(1.0)]);
// An unclosed one ends at the end of the data.
let mut lx = crate::object::Lexer::new(b"[ 1 2 ", 0);
lx.skip_compound();
assert_eq!(lx.pos, 6);
}
#[test]
fn skipped_calculator_tokens_count_toward_the_cap() {
// `null` is not a calculator token: skipped, but still scanned.
let src = format!("{{ {}}}", "null ".repeat(MAX_CALC_OPS + 10));
let mut lx = crate::object::Lexer::new(src.as_bytes(), 0);
let mut scanned = 0;
ps_parse(&mut lx, 0, &mut scanned);
assert!(scanned > MAX_CALC_OPS && scanned < MAX_CALC_OPS + 10, "parsing stops once the cap is passed ({scanned})");
}
#[test]
fn calculator_functions() {
// Two inputs → three outputs: { 2 copy mul 3 1 roll add 2 div dup 0.5 gt { pop 1 } if 0 }
let code = b"{ 2 copy mul 3 1 roll add 2 div dup 0.5 gt { pop 1 } { 0.25 mul } ifelse 0 }";
let mut lx = crate::object::Lexer::new(code, 0);
let Some(PsOp::Proc(code)) = ps_parse(&mut lx, 0).into_iter().next() else { panic!() };
let Some(PsOp::Proc(code)) = ps_parse(&mut lx, 0, &mut 0).into_iter().next() else { panic!() };
let f = Func::Calc { domain: vec![0.0, 1.0, 0.0, 1.0], range: vec![0.0, 1.0, 0.0, 1.0, 0.0, 1.0], code };
assert_eq!(f.eval(&[0.5, 0.4]), vec![0.2, 0.1125, 0.0]);
assert_eq!(f.eval(&[1.0, 0.8]), vec![0.8, 1.0, 0.0]);
@@ -771,7 +867,7 @@ mod tests {
fn run(src: &str, mut st: Vec<f64>) -> Vec<f64> {
let src = format!("{{ {src} }}");
let mut lx = crate::object::Lexer::new(src.as_bytes(), 0);
let Some(PsOp::Proc(code)) = ps_parse(&mut lx, 0).into_iter().next() else { panic!() };
let Some(PsOp::Proc(code)) = ps_parse(&mut lx, 0, &mut 0).into_iter().next() else { panic!() };
ps_run(&code, &mut st, 0);
st
}
+85
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@@ -82,6 +82,91 @@ impl<'a> Lexer<'a> {
}
}
/// Whether the next token opens an array or a dictionary (skipping white space first).
pub fn at_compound(&mut self) -> bool {
self.skip_ws();
match self.data.get(self.pos) {
Some(b'[') => true,
Some(b'<') => self.data.get(self.pos + 1) == Some(&b'<'),
_ => false,
}
}
/// Skip the array or dictionary at the current position (see [`Lexer::at_compound`]) as
/// [`Lexer::next`] would read it, without building it: for readers that have no use for one
/// and must not allocate a vector per element of a hostile stream.
pub fn skip_compound(&mut self) {
let mut open = 0usize;
loop {
self.skip_ws();
match self.data.get(self.pos) {
None => return,
Some(b'[') => {
open += 1;
self.pos += 1;
}
Some(b'<') if self.data.get(self.pos + 1) == Some(&b'<') => {
open += 1;
self.pos += 2;
}
Some(b']') | Some(b'>') if self.data[self.pos] == b']' || self.data.get(self.pos + 1) == Some(&b'>') => {
open = open.saturating_sub(1);
self.pos += if self.data[self.pos] == b']' { 1 } else { 2 };
if open == 0 {
return;
}
}
// Anything else is one token (a string, name, number or word), passed over
// without building it.
Some(_) => self.skip_scalar(),
}
}
}
/// Pass over one token that is not an array or dictionary bracket, as [`Lexer::next`] reads
/// it but without building its value.
fn skip_scalar(&mut self) {
let Some(&c) = self.data.get(self.pos) else { return };
match c {
b'(' => {
// A literal string: balanced parentheses, a backslash escapes the next byte.
let mut depth = 0usize;
while let Some(&d) = self.data.get(self.pos) {
self.pos += 1;
match d {
b'\\' => self.pos += 1,
b'(' => depth += 1,
b')' => {
depth -= 1;
if depth == 0 {
break;
}
}
_ => {}
}
}
self.pos = self.pos.min(self.data.len());
}
b'<' => {
// A hexadecimal string.
while self.data.get(self.pos).is_some_and(|d| *d != b'>') {
self.pos += 1;
}
self.pos = (self.pos + 1).min(self.data.len());
}
b'/' => {
self.pos += 1;
self.word();
}
b']' | b'{' | b'}' | b')' | b'>' => self.pos += 1,
_ => {
if self.word().is_empty() {
self.pos += 1;
}
}
}
}
fn word(&mut self) -> &'a [u8] {
let s = self.pos;
while self.pos < self.data.len() && !is_white(self.data[self.pos]) && !is_delim(self.data[self.pos]) {
+12 -1
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@@ -18,6 +18,8 @@ const MAX_SIDE: f64 = 1024.0;
const MAX_SCALE: f64 = 4.0;
/// The most triangles one shading draws.
const MAX_TRIANGLES: usize = 2_000_000;
/// How many times over the mesh raster may be covered by triangle bounding boxes in all.
const MAX_RASTER_PASSES: usize = 64;
/// A mesh vertex: page-space position and its value (RGB, or `t` in `[0]` with a function).
#[derive(Clone, Copy, Debug, PartialEq)]
@@ -234,13 +236,17 @@ fn free_form(r: &mut Bits, l: &Layout, colors: &Colors, m: Affine) -> Vec<[V; 3]
/// Type 5: a lattice of `per_row` vertices per row, two triangles per cell.
fn lattice(r: &mut Bits, l: &Layout, colors: &Colors, m: Affine, per_row: usize) -> Vec<[V; 3]> {
if per_row < 2 {
if !(2..=MAX_TRIANGLES).contains(&per_row) {
return vec![];
}
let mut rows: Vec<Vec<V>> = vec![];
let mut row = vec![];
while let (Some(p), Some(c)) = (l.point(r), l.comps(r)) {
r.align();
// Vertices kept, the unfinished row's included, stay within the triangle limit.
if (rows.len() * per_row).saturating_add(row.len()) >= MAX_TRIANGLES {
break;
}
row.push(V { p: m * p, c: colors.value(&c) });
if row.len() == per_row {
rows.push(std::mem::take(&mut row));
@@ -447,6 +453,9 @@ fn rasterize(tris: &[[V; 3]], colors: &Colors, page_box: [f64; 4]) -> Option<Svg
let ss = s * 2.0;
let mut val = vec![[0.0f32; 3]; sw * sh];
let mut cov = vec![false; sw * sh];
// Samples tested across all triangles: overlapping triangles that each cover the raster
// would otherwise test it once per triangle. Past the budget the later triangles are left out.
let mut work = (sw * sh).saturating_mul(MAX_RASTER_PASSES).saturating_add(tris.len().saturating_mul(16));
for t in tris {
let q = t.map(|v| Point::new((v.p.x - o.x) * ss, (o.y - v.p.y) * ss));
let area = (q[1].x - q[0].x) * (q[2].y - q[0].y) - (q[2].x - q[0].x) * (q[1].y - q[0].y);
@@ -457,6 +466,8 @@ fn rasterize(tris: &[[V; 3]], colors: &Colors, page_box: [f64; 4]) -> Option<Svg
let by0 = q.iter().map(|p| p.y).fold(f64::MAX, f64::min).floor().max(0.0) as usize;
let bx1 = (q.iter().map(|p| p.x).fold(f64::MIN, f64::max).ceil().max(0.0) as usize).min(sw);
let by1 = (q.iter().map(|p| p.y).fold(f64::MIN, f64::max).ceil().max(0.0) as usize).min(sh);
let Some(left) = work.checked_sub(bx1.saturating_sub(bx0).saturating_mul(by1.saturating_sub(by0))) else { break };
work = left;
let eps = 1e-9 * area.abs();
for y in by0..by1 {
for x in bx0..bx1 {
+29
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@@ -1125,6 +1125,35 @@ fn a_fanning_out_reference_graph_is_refused_within_the_budget() {
assert_eq!(read_function(objs), color::Func::Unsupported);
}
#[test]
fn a_sampled_function_shorter_than_its_table_is_refused() {
// 4,096 8-bit samples declared, ten bytes given: the missing ones are not made up.
let f = "<< /FunctionType 0 /Domain [0 1] /Size [4096] /Range [0 1] /BitsPerSample 8 >>";
assert_eq!(read_function(vec![(1, f.into(), Some(vec![7; 10]))]), color::Func::Unsupported);
assert_ne!(read_function(vec![(1, f.into(), Some(vec![7; 4096]))]), color::Func::Unsupported);
}
#[test]
fn a_calculator_program_past_the_operator_limit_is_refused() {
let f = "<< /FunctionType 4 /Domain [0 1] /Range [0 1] >>";
let long = format!("{{ {} }}", "1 pop ".repeat(3000));
assert_eq!(read_function(vec![(1, f.into(), Some(long.into_bytes()))]), color::Func::Unsupported);
assert_ne!(read_function(vec![(1, f.into(), Some(b"{ 1 exch sub }".to_vec()))]), color::Func::Unsupported);
}
#[test]
fn copies_of_a_function_are_charged_for_its_coefficients() {
// A stitching function listing one object 1,000 times, whose coefficient arrays hold 2,000
// values: each copy is charged its values, so the budget refuses it instead of copying
// two million values.
let c = format!("[{}]", "0.5 ".repeat(1000));
let objs: Objs = vec![
(1, format!("<< /FunctionType 3 /Domain [0 1] /Functions [{}] >>", "2 0 R ".repeat(1000)), None),
(2, format!("<< /FunctionType 2 /Domain [0 1] /C0 {c} /C1 {c} /N 1 >>"), None),
];
assert_eq!(read_function(objs), color::Func::Unsupported);
}
#[test]
fn colour_space_chain_of_depth_3() {
// Indexed → Separation → ICCBased → DeviceRGB: entry 0 is tint 1 (blue), entry 1 tint 0 (white).
+29
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@@ -262,3 +262,32 @@ fn corrupt_mesh_data_draws_what_parses() {
let doc = parse(&bytes).unwrap();
assert!(doc.skipped.iter().any(|s| s.contains("layout")), "{:?}", doc.skipped);
}
#[test]
fn overlapping_mesh_triangles_stop_at_the_raster_budget() {
// 20,000 triangles each covering the whole page would test every sample 20,000 times; the
// raster budget stops after about 64 passes, and the shading is still drawn.
let mut m = Mesh::default();
for _ in 0..20_000 {
m.flag(0).pt(0, 0).c(&[255, 0, 0]);
m.flag(0).pt(400, 0).c(&[255, 0, 0]);
m.flag(0).pt(0, 400).c(&[255, 0, 0]);
}
let sh = format!("<< /ShadingType 4 /ColorSpace /DeviceRGB /BitsPerCoordinate 16 /BitsPerComponent 8 /BitsPerFlag 8 {RGB_DECODE} >>");
let bytes = page_pdf("/Sh sh", "/Shading << /Sh 10 0 R >>", vec![(10, sh, Some(m.0))]);
let (tx, rx) = std::sync::mpsc::channel();
std::thread::spawn(move || tx.send(parse(&bytes)).ok());
let doc = rx.recv_timeout(std::time::Duration::from_secs(20)).expect("the mesh finishes").unwrap();
assert!(render(&doc).get(50, 50)[0] > 0.99);
}
#[test]
fn a_lattice_row_longer_than_the_triangle_limit_draws_nothing() {
let mut m = Mesh::default();
for i in 0..8 {
m.pt(i * 10, 0).c(&[255, 0, 0]);
}
let sh = format!("<< /ShadingType 5 /ColorSpace /DeviceRGB /BitsPerCoordinate 16 /BitsPerComponent 8 /VerticesPerRow 3000000 {RGB_DECODE} >>");
let doc = parse(&page_pdf("/Sh sh", "/Shading << /Sh 10 0 R >>", vec![(10, sh, Some(m.0))])).unwrap();
assert!(doc.flatten().is_empty());
}