From 46846a337e8084acd46c70bccc2fca2659e9fb9a Mon Sep 17 00:00:00 2001
From: Laurenz <laurmaedje@gmail.com>
Date: Wed, 8 Nov 2023 14:32:42 +0100
Subject: Extract `typst-pdf` crate

---
 crates/typst-pdf/src/gradient.rs | 581 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 581 insertions(+)
 create mode 100644 crates/typst-pdf/src/gradient.rs

(limited to 'crates/typst-pdf/src/gradient.rs')

diff --git a/crates/typst-pdf/src/gradient.rs b/crates/typst-pdf/src/gradient.rs
new file mode 100644
index 00000000..e5cae30e
--- /dev/null
+++ b/crates/typst-pdf/src/gradient.rs
@@ -0,0 +1,581 @@
+use std::f32::consts::{PI, TAU};
+use std::sync::Arc;
+
+use ecow::{eco_format, EcoString};
+use pdf_writer::types::FunctionShadingType;
+use pdf_writer::writers::StreamShadingType;
+use pdf_writer::{types::ColorSpaceOperand, Name};
+use pdf_writer::{Filter, Finish, Ref};
+use typst::geom::{
+    Abs, Angle, Color, ColorSpace, ConicGradient, Gradient, Numeric, Point, Quadrant,
+    Ratio, Relative, Transform, WeightedColor,
+};
+
+use crate::color::{ColorSpaceExt, PaintEncode, QuantizedColor};
+use crate::page::{PageContext, Transforms};
+use crate::{deflate, AbsExt, PdfContext};
+
+/// A unique-transform-aspect-ratio combination that will be encoded into the
+/// PDF.
+#[derive(Debug, Clone, Eq, PartialEq, Hash)]
+pub struct PdfGradient {
+    /// The transform to apply to the gradient.
+    pub transform: Transform,
+    /// The aspect ratio of the gradient.
+    /// Required for aspect ratio correction.
+    pub aspect_ratio: Ratio,
+    /// The gradient.
+    pub gradient: Gradient,
+    /// Whether the gradient is applied to text.
+    pub on_text: bool,
+}
+
+/// Writes the actual gradients (shading patterns) to the PDF.
+/// This is performed once after writing all pages.
+pub fn write_gradients(ctx: &mut PdfContext) {
+    for PdfGradient { transform, aspect_ratio, gradient, on_text } in
+        ctx.gradient_map.items().cloned().collect::<Vec<_>>()
+    {
+        let shading = ctx.alloc.bump();
+        ctx.gradient_refs.push(shading);
+
+        let mut shading_pattern = match &gradient {
+            Gradient::Linear(linear) => {
+                let shading_function = shading_function(ctx, &gradient);
+                let mut shading_pattern = ctx.pdf.shading_pattern(shading);
+                let mut shading = shading_pattern.function_shading();
+                shading.shading_type(FunctionShadingType::Axial);
+
+                ctx.colors
+                    .write(gradient.space(), shading.color_space(), &mut ctx.alloc);
+
+                let angle = Gradient::correct_aspect_ratio(linear.angle, aspect_ratio);
+                let (sin, cos) = (angle.sin(), angle.cos());
+                let length = sin.abs() + cos.abs();
+
+                shading
+                    .anti_alias(gradient.anti_alias())
+                    .function(shading_function)
+                    .coords([0.0, 0.0, length as f32, 0.0])
+                    .extend([true; 2]);
+
+                shading.finish();
+
+                shading_pattern
+            }
+            Gradient::Radial(radial) => {
+                let shading_function = shading_function(ctx, &gradient);
+                let mut shading_pattern = ctx.pdf.shading_pattern(shading);
+                let mut shading = shading_pattern.function_shading();
+                shading.shading_type(FunctionShadingType::Radial);
+
+                ctx.colors
+                    .write(gradient.space(), shading.color_space(), &mut ctx.alloc);
+
+                shading
+                    .anti_alias(gradient.anti_alias())
+                    .function(shading_function)
+                    .coords([
+                        radial.focal_center.x.get() as f32,
+                        radial.focal_center.y.get() as f32,
+                        radial.focal_radius.get() as f32,
+                        radial.center.x.get() as f32,
+                        radial.center.y.get() as f32,
+                        radial.radius.get() as f32,
+                    ])
+                    .extend([true; 2]);
+
+                shading.finish();
+
+                shading_pattern
+            }
+            Gradient::Conic(conic) => {
+                let vertices = compute_vertex_stream(conic, aspect_ratio, on_text);
+
+                let stream_shading_id = ctx.alloc.bump();
+                let mut stream_shading =
+                    ctx.pdf.stream_shading(stream_shading_id, &vertices);
+
+                ctx.colors.write(
+                    conic.space,
+                    stream_shading.color_space(),
+                    &mut ctx.alloc,
+                );
+
+                let range = conic.space.range();
+                stream_shading
+                    .bits_per_coordinate(16)
+                    .bits_per_component(16)
+                    .bits_per_flag(8)
+                    .shading_type(StreamShadingType::CoonsPatch)
+                    .decode([
+                        0.0, 1.0, 0.0, 1.0, range[0], range[1], range[2], range[3],
+                        range[4], range[5],
+                    ])
+                    .anti_alias(gradient.anti_alias())
+                    .filter(Filter::FlateDecode);
+
+                stream_shading.finish();
+
+                let mut shading_pattern = ctx.pdf.shading_pattern(shading);
+                shading_pattern.shading_ref(stream_shading_id);
+                shading_pattern
+            }
+        };
+
+        shading_pattern.matrix(transform_to_array(transform));
+    }
+}
+
+/// Writes an expotential or stitched function that expresses the gradient.
+fn shading_function(ctx: &mut PdfContext, gradient: &Gradient) -> Ref {
+    let function = ctx.alloc.bump();
+    let mut functions = vec![];
+    let mut bounds = vec![];
+    let mut encode = vec![];
+
+    // Create the individual gradient functions for each pair of stops.
+    for window in gradient.stops_ref().windows(2) {
+        let (first, second) = (window[0], window[1]);
+
+        // Skip stops with the same position.
+        if first.1.get() == second.1.get() {
+            continue;
+        }
+
+        // If the color space is HSL or HSV, and we cross the 0°/360° boundary,
+        // we need to create two separate stops.
+        if gradient.space() == ColorSpace::Hsl || gradient.space() == ColorSpace::Hsv {
+            let t1 = first.1.get() as f32;
+            let t2 = second.1.get() as f32;
+            let [h1, s1, x1, _] = first.0.to_space(gradient.space()).to_vec4();
+            let [h2, s2, x2, _] = second.0.to_space(gradient.space()).to_vec4();
+
+            // Compute the intermediary stop at 360°.
+            if (h1 - h2).abs() > 180.0 {
+                let h1 = if h1 < h2 { h1 + 360.0 } else { h1 };
+                let h2 = if h2 < h1 { h2 + 360.0 } else { h2 };
+
+                // We compute where the crossing happens between zero and one
+                let t = (360.0 - h1) / (h2 - h1);
+                // We then map it back to the original range.
+                let t_prime = t * (t2 - t1) + t1;
+
+                // If the crossing happens between the two stops,
+                // we need to create an extra stop.
+                if t_prime <= t2 && t_prime >= t1 {
+                    bounds.push(t_prime);
+                    bounds.push(t_prime);
+                    bounds.push(t2);
+                    encode.extend([0.0, 1.0]);
+                    encode.extend([0.0, 1.0]);
+                    encode.extend([0.0, 1.0]);
+
+                    // These need to be individual function to encode 360.0 correctly.
+                    let func1 = ctx.alloc.bump();
+                    ctx.pdf
+                        .exponential_function(func1)
+                        .range(gradient.space().range())
+                        .c0(gradient.space().convert(first.0))
+                        .c1([1.0, s1 * (1.0 - t) + s2 * t, x1 * (1.0 - t) + x2 * t])
+                        .domain([0.0, 1.0])
+                        .n(1.0);
+
+                    let func2 = ctx.alloc.bump();
+                    ctx.pdf
+                        .exponential_function(func2)
+                        .range(gradient.space().range())
+                        .c0([1.0, s1 * (1.0 - t) + s2 * t, x1 * (1.0 - t) + x2 * t])
+                        .c1([0.0, s1 * (1.0 - t) + s2 * t, x1 * (1.0 - t) + x2 * t])
+                        .domain([0.0, 1.0])
+                        .n(1.0);
+
+                    let func3 = ctx.alloc.bump();
+                    ctx.pdf
+                        .exponential_function(func3)
+                        .range(gradient.space().range())
+                        .c0([0.0, s1 * (1.0 - t) + s2 * t, x1 * (1.0 - t) + x2 * t])
+                        .c1(gradient.space().convert(second.0))
+                        .domain([0.0, 1.0])
+                        .n(1.0);
+
+                    functions.push(func1);
+                    functions.push(func2);
+                    functions.push(func3);
+
+                    continue;
+                }
+            }
+        }
+
+        bounds.push(second.1.get() as f32);
+        functions.push(single_gradient(ctx, first.0, second.0, gradient.space()));
+        encode.extend([0.0, 1.0]);
+    }
+
+    // Special case for gradients with only two stops.
+    if functions.len() == 1 {
+        return functions[0];
+    }
+
+    // Remove the last bound, since it's not needed for the stitching function.
+    bounds.pop();
+
+    // Create the stitching function.
+    ctx.pdf
+        .stitching_function(function)
+        .domain([0.0, 1.0])
+        .range(gradient.space().range())
+        .functions(functions)
+        .bounds(bounds)
+        .encode(encode);
+
+    function
+}
+
+/// Writes an expontential function that expresses a single segment (between two
+/// stops) of a gradient.
+fn single_gradient(
+    ctx: &mut PdfContext,
+    first_color: Color,
+    second_color: Color,
+    color_space: ColorSpace,
+) -> Ref {
+    let reference = ctx.alloc.bump();
+
+    ctx.pdf
+        .exponential_function(reference)
+        .range(color_space.range())
+        .c0(color_space.convert(first_color))
+        .c1(color_space.convert(second_color))
+        .domain([0.0, 1.0])
+        .n(1.0);
+
+    reference
+}
+
+impl PaintEncode for Gradient {
+    fn set_as_fill(&self, ctx: &mut PageContext, on_text: bool, transforms: Transforms) {
+        ctx.reset_fill_color_space();
+
+        let id = register_gradient(ctx, self, on_text, transforms);
+        let name = Name(id.as_bytes());
+
+        ctx.content.set_fill_color_space(ColorSpaceOperand::Pattern);
+        ctx.content.set_fill_pattern(None, name);
+    }
+
+    fn set_as_stroke(
+        &self,
+        ctx: &mut PageContext,
+        on_text: bool,
+        transforms: Transforms,
+    ) {
+        ctx.reset_stroke_color_space();
+
+        let id = register_gradient(ctx, self, on_text, transforms);
+        let name = Name(id.as_bytes());
+
+        ctx.content.set_stroke_color_space(ColorSpaceOperand::Pattern);
+        ctx.content.set_stroke_pattern(None, name);
+    }
+}
+
+/// Deduplicates a gradient to a named PDF resource.
+fn register_gradient(
+    ctx: &mut PageContext,
+    gradient: &Gradient,
+    on_text: bool,
+    mut transforms: Transforms,
+) -> EcoString {
+    // Edge cases for strokes.
+    if transforms.size.x.is_zero() {
+        transforms.size.x = Abs::pt(1.0);
+    }
+
+    if transforms.size.y.is_zero() {
+        transforms.size.y = Abs::pt(1.0);
+    }
+
+    let size = match gradient.unwrap_relative(on_text) {
+        Relative::Self_ => transforms.size,
+        Relative::Parent => transforms.container_size,
+    };
+
+    // Correction for y-axis flipping on text.
+    let angle = gradient.angle().unwrap_or_else(Angle::zero);
+    let angle = if on_text { Angle::rad(TAU as f64) - angle } else { angle };
+
+    let (offset_x, offset_y) = match gradient {
+        Gradient::Conic(conic) => (
+            -size.x * (1.0 - conic.center.x.get() / 2.0) / 2.0,
+            -size.y * (1.0 - conic.center.y.get() / 2.0) / 2.0,
+        ),
+        _ => match angle.quadrant() {
+            Quadrant::First => (Abs::zero(), Abs::zero()),
+            Quadrant::Second => (size.x, Abs::zero()),
+            Quadrant::Third => (size.x, size.y),
+            Quadrant::Fourth => (Abs::zero(), size.y),
+        },
+    };
+
+    let rotation = match gradient {
+        Gradient::Conic(_) => Angle::zero(),
+        _ => angle,
+    };
+
+    let transform = match gradient.unwrap_relative(on_text) {
+        Relative::Self_ => transforms.transform,
+        Relative::Parent => transforms.container_transform,
+    };
+
+    let scale_offset = match gradient {
+        Gradient::Conic(_) => 4.0_f64,
+        _ => 1.0,
+    };
+
+    let pdf_gradient = PdfGradient {
+        aspect_ratio: size.aspect_ratio(),
+        transform: transform
+            .pre_concat(Transform::translate(
+                offset_x * scale_offset,
+                offset_y * scale_offset,
+            ))
+            .pre_concat(Transform::scale(
+                Ratio::new(size.x.to_pt() * scale_offset),
+                Ratio::new(size.y.to_pt() * scale_offset),
+            ))
+            .pre_concat(Transform::rotate(Gradient::correct_aspect_ratio(
+                rotation,
+                size.aspect_ratio(),
+            ))),
+        gradient: gradient.clone(),
+        on_text,
+    };
+
+    let index = ctx.parent.gradient_map.insert(pdf_gradient);
+    eco_format!("Gr{}", index)
+}
+
+/// Convert to an array of floats.
+fn transform_to_array(ts: Transform) -> [f32; 6] {
+    [
+        ts.sx.get() as f32,
+        ts.ky.get() as f32,
+        ts.kx.get() as f32,
+        ts.sy.get() as f32,
+        ts.tx.to_f32(),
+        ts.ty.to_f32(),
+    ]
+}
+
+/// Writes a single Coons Patch as defined in the PDF specification
+/// to a binary vec.
+///
+/// Structure:
+///  - flag: `u8`
+///  - points: `[u16; 24]`
+///  - colors: `[u16; 12]`
+fn write_patch(
+    target: &mut Vec<u8>,
+    t: f32,
+    t1: f32,
+    c0: [u16; 3],
+    c1: [u16; 3],
+    angle: Angle,
+    on_text: bool,
+) {
+    let mut theta = -TAU * t + angle.to_rad() as f32 + PI;
+    let mut theta1 = -TAU * t1 + angle.to_rad() as f32 + PI;
+
+    // Correction for y-axis flipping on text.
+    if on_text {
+        theta = (TAU - theta).rem_euclid(TAU);
+        theta1 = (TAU - theta1).rem_euclid(TAU);
+    }
+
+    let (cp1, cp2) =
+        control_point(Point::new(Abs::pt(0.5), Abs::pt(0.5)), 0.5, theta, theta1);
+
+    // Push the flag
+    target.push(0);
+
+    let p1 =
+        [u16::quantize(0.5, [0.0, 1.0]).to_be(), u16::quantize(0.5, [0.0, 1.0]).to_be()];
+
+    let p2 = [
+        u16::quantize(theta.cos(), [-1.0, 1.0]).to_be(),
+        u16::quantize(theta.sin(), [-1.0, 1.0]).to_be(),
+    ];
+
+    let p3 = [
+        u16::quantize(theta1.cos(), [-1.0, 1.0]).to_be(),
+        u16::quantize(theta1.sin(), [-1.0, 1.0]).to_be(),
+    ];
+
+    let cp1 = [
+        u16::quantize(cp1.x.to_f32(), [0.0, 1.0]).to_be(),
+        u16::quantize(cp1.y.to_f32(), [0.0, 1.0]).to_be(),
+    ];
+
+    let cp2 = [
+        u16::quantize(cp2.x.to_f32(), [0.0, 1.0]).to_be(),
+        u16::quantize(cp2.y.to_f32(), [0.0, 1.0]).to_be(),
+    ];
+
+    // Push the points
+    target.extend_from_slice(bytemuck::cast_slice(&[
+        p1, p1, p2, p2, cp1, cp2, p3, p3, p1, p1, p1, p1,
+    ]));
+
+    let colors =
+        [c0.map(u16::to_be), c0.map(u16::to_be), c1.map(u16::to_be), c1.map(u16::to_be)];
+
+    // Push the colors.
+    target.extend_from_slice(bytemuck::cast_slice(&colors));
+}
+
+fn control_point(c: Point, r: f32, angle_start: f32, angle_end: f32) -> (Point, Point) {
+    let n = (TAU / (angle_end - angle_start)).abs();
+    let f = ((angle_end - angle_start) / n).tan() * 4.0 / 3.0;
+
+    let p1 = c + Point::new(
+        Abs::pt((r * angle_start.cos() - f * r * angle_start.sin()) as f64),
+        Abs::pt((r * angle_start.sin() + f * r * angle_start.cos()) as f64),
+    );
+
+    let p2 = c + Point::new(
+        Abs::pt((r * angle_end.cos() + f * r * angle_end.sin()) as f64),
+        Abs::pt((r * angle_end.sin() - f * r * angle_end.cos()) as f64),
+    );
+
+    (p1, p2)
+}
+
+#[comemo::memoize]
+fn compute_vertex_stream(
+    conic: &ConicGradient,
+    aspect_ratio: Ratio,
+    on_text: bool,
+) -> Arc<Vec<u8>> {
+    // Generated vertices for the Coons patches
+    let mut vertices = Vec::new();
+
+    // Correct the gradient's angle
+    let angle = Gradient::correct_aspect_ratio(conic.angle, aspect_ratio);
+
+    // We want to generate a vertex based on some conditions, either:
+    // - At the boundary of a stop
+    // - At the boundary of a quadrant
+    // - When we cross the boundary of a hue turn (for HSV and HSL only)
+    for window in conic.stops.windows(2) {
+        let ((c0, t0), (c1, t1)) = (window[0], window[1]);
+
+        // Skip stops with the same position
+        if t0 == t1 {
+            continue;
+        }
+
+        // If the angle between the two stops is greater than 90 degrees, we need to
+        // generate a vertex at the boundary of the quadrant.
+        // However, we add more stops in-between to make the gradient smoother, so we
+        // need to generate a vertex at least every 5 degrees.
+        // If the colors are the same, we do it every quadrant only.
+        let slope = 1.0 / (t1.get() - t0.get());
+        let mut t_x = t0.get();
+        let dt = (t1.get() - t0.get()).min(0.25);
+        while t_x < t1.get() {
+            let t_next = (t_x + dt).min(t1.get());
+
+            let t1 = slope * (t_x - t0.get());
+            let t2 = slope * (t_next - t0.get());
+
+            // We don't use `Gradient::sample` to avoid issues with sharp gradients.
+            let c = Color::mix_iter(
+                [WeightedColor::new(c0, 1.0 - t1), WeightedColor::new(c1, t1)],
+                conic.space,
+            )
+            .unwrap();
+
+            let c_next = Color::mix_iter(
+                [WeightedColor::new(c0, 1.0 - t2), WeightedColor::new(c1, t2)],
+                conic.space,
+            )
+            .unwrap();
+
+            // If the color space is HSL or HSV, and we cross the 0°/360° boundary,
+            // we need to create two separate stops.
+            if conic.space == ColorSpace::Hsl || conic.space == ColorSpace::Hsv {
+                let [h1, s1, x1, _] = c.to_space(conic.space).to_vec4();
+                let [h2, s2, x2, _] = c_next.to_space(conic.space).to_vec4();
+
+                // Compute the intermediary stop at 360°.
+                if (h1 - h2).abs() > 180.0 {
+                    let h1 = if h1 < h2 { h1 + 360.0 } else { h1 };
+                    let h2 = if h2 < h1 { h2 + 360.0 } else { h2 };
+
+                    // We compute where the crossing happens between zero and one
+                    let t = (360.0 - h1) / (h2 - h1);
+                    // We then map it back to the original range.
+                    let t_prime = t * (t_next as f32 - t_x as f32) + t_x as f32;
+
+                    // If the crossing happens between the two stops,
+                    // we need to create an extra stop.
+                    if t_prime <= t_next as f32 && t_prime >= t_x as f32 {
+                        let c0 = [1.0, s1 * (1.0 - t) + s2 * t, x1 * (1.0 - t) + x2 * t];
+                        let c1 = [0.0, s1 * (1.0 - t) + s2 * t, x1 * (1.0 - t) + x2 * t];
+                        let c0 = c0.map(|c| u16::quantize(c, [0.0, 1.0]));
+                        let c1 = c1.map(|c| u16::quantize(c, [0.0, 1.0]));
+
+                        write_patch(
+                            &mut vertices,
+                            t_x as f32,
+                            t_prime,
+                            conic.space.convert(c),
+                            c0,
+                            angle,
+                            on_text,
+                        );
+
+                        write_patch(
+                            &mut vertices,
+                            t_prime,
+                            t_prime,
+                            c0,
+                            c1,
+                            angle,
+                            on_text,
+                        );
+
+                        write_patch(
+                            &mut vertices,
+                            t_prime,
+                            t_next as f32,
+                            c1,
+                            conic.space.convert(c_next),
+                            angle,
+                            on_text,
+                        );
+
+                        t_x = t_next;
+                        continue;
+                    }
+                }
+            }
+
+            write_patch(
+                &mut vertices,
+                t_x as f32,
+                t_next as f32,
+                conic.space.convert(c),
+                conic.space.convert(c_next),
+                angle,
+                on_text,
+            );
+
+            t_x = t_next;
+        }
+    }
+
+    Arc::new(deflate(&vertices))
+}
-- 
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