Add paint stroke sampling tests

CMakeLists.txt

@@ -94,7 +94,8 @@ target_link_libraries(pp_assets
         pp_project_warnings)
 
 add_library(pp_paint STATIC
-    src/paint/blend.cpp)
+    src/paint/blend.cpp
+    src/paint/stroke.cpp)
 target_include_directories(pp_paint
     PUBLIC
         "${CMAKE_CURRENT_SOURCE_DIR}/src")

docs/modernization/build-inventory.md

@@ -80,7 +80,7 @@ Known local toolchain state:
   `platform-build` automation wrapper for `pp_foundation`, `pp_assets`,
   `pp_paint`, `pp_document`, `pp_renderer_api`, `pp_paint_renderer`,
   `pp_ui_core`, `pano_cli`, and their current headless test binaries,
-  including PPI header and layout XML parse coverage.
+  including PPI header, paint stroke sampling, and layout XML parse coverage.
 - `panopainter_validate_shaders` validates the current combined GLSL shader
   files for one vertex stage marker, one fragment stage marker, valid marker
   order, and existing relative includes.

docs/modernization/roadmap.md

@@ -309,9 +309,10 @@ and stroke timing spans with invalid-end tests. `pp_assets` has started with
 PNG/JPEG signature detection plus PPI header recognition, with
 corrupt/truncated/unsupported tests.
 `pp_paint` has started with CPU reference math for the five current shader
-blend modes. `pp_document` has started with a pure canvas/layer/frame model
-and layer/frame/undo-redo history invariant tests. `pp_renderer_api` has started
-with renderer-neutral texture/readback descriptors and validation tests. `pp_paint_renderer` has
+blend modes plus deterministic stroke spacing/interpolation. `pp_document` has
+started with a pure canvas/layer/frame model and layer/frame/undo-redo history
+invariant tests. `pp_renderer_api` has started with renderer-neutral
+texture/readback descriptors and validation tests. `pp_paint_renderer` has
 started with deterministic CPU layer compositing over renderer extents using
 the paint blend reference. `pp_ui_core` has started with XML-layout-facing
 length parsing, tinyxml-backed layout XML parsing, and invalid input tests.
@@ -521,7 +522,7 @@ Last verified on 2026-06-01:
 
 ```powershell
 cmake --preset windows-msvc-default
-cmake --build --preset windows-msvc-default --config Debug --target pp_foundation_binary_stream_tests pp_foundation_parse_tests pp_foundation_trace_tests pp_assets_image_format_tests pp_assets_ppi_header_tests pp_paint_blend_tests pp_document_tests pp_renderer_api_tests pp_paint_renderer_compositor_tests pp_ui_core_layout_value_tests pp_ui_core_layout_xml_tests pano_cli PanoPainter
+cmake --build --preset windows-msvc-default --config Debug --target pp_foundation_binary_stream_tests pp_foundation_parse_tests pp_foundation_trace_tests pp_assets_image_format_tests pp_assets_ppi_header_tests pp_paint_blend_tests pp_paint_stroke_tests pp_document_tests pp_renderer_api_tests pp_paint_renderer_compositor_tests pp_ui_core_layout_value_tests pp_ui_core_layout_xml_tests pano_cli PanoPainter
 ctest --preset desktop-fast --build-config Debug
 powershell -ExecutionPolicy Bypass -File scripts\automation\test.ps1 -Preset desktop-fast -Configuration Debug
 powershell -ExecutionPolicy Bypass -File scripts\automation\build.ps1 -Preset windows-msvc-default -Configuration Debug -Target pano_cli
@@ -540,6 +541,7 @@ Results:
 - `pp_assets_image_format_tests` passed.
 - `pp_assets_ppi_header_tests` passed.
 - `pp_paint_blend_tests` passed.
+- `pp_paint_stroke_tests` passed.
 - `pp_document_tests` passed.
 - `pp_renderer_api_tests` passed.
 - `pp_paint_renderer_compositor_tests` passed.

scripts/automation/platform-build.ps1

@@ -1,7 +1,7 @@
 [CmdletBinding()]
 param(
     [string[]]$Presets = @("android-arm64"),
-    [string[]]$Targets = @("pp_foundation", "pp_assets", "pp_paint", "pp_document", "pp_renderer_api", "pp_paint_renderer", "pp_ui_core", "pano_cli", "pp_foundation_binary_stream_tests", "pp_foundation_parse_tests", "pp_foundation_trace_tests", "pp_assets_image_format_tests", "pp_assets_ppi_header_tests", "pp_paint_blend_tests", "pp_document_tests", "pp_renderer_api_tests", "pp_paint_renderer_compositor_tests", "pp_ui_core_layout_value_tests", "pp_ui_core_layout_xml_tests")
+    [string[]]$Targets = @("pp_foundation", "pp_assets", "pp_paint", "pp_document", "pp_renderer_api", "pp_paint_renderer", "pp_ui_core", "pano_cli", "pp_foundation_binary_stream_tests", "pp_foundation_parse_tests", "pp_foundation_trace_tests", "pp_assets_image_format_tests", "pp_assets_ppi_header_tests", "pp_paint_blend_tests", "pp_paint_stroke_tests", "pp_document_tests", "pp_renderer_api_tests", "pp_paint_renderer_compositor_tests", "pp_ui_core_layout_value_tests", "pp_ui_core_layout_xml_tests")
 )
 
 $ErrorActionPreference = "Stop"

scripts/automation/platform-build.sh

@@ -3,7 +3,7 @@ set -u
 
 preset="${1:-android-arm64}"
 shift || true
-targets="${*:-pp_foundation pp_assets pp_paint pp_document pp_renderer_api pp_paint_renderer pp_ui_core pano_cli pp_foundation_binary_stream_tests pp_foundation_parse_tests pp_foundation_trace_tests pp_assets_image_format_tests pp_assets_ppi_header_tests pp_paint_blend_tests pp_document_tests pp_renderer_api_tests pp_paint_renderer_compositor_tests pp_ui_core_layout_value_tests pp_ui_core_layout_xml_tests}"
+targets="${*:-pp_foundation pp_assets pp_paint pp_document pp_renderer_api pp_paint_renderer pp_ui_core pano_cli pp_foundation_binary_stream_tests pp_foundation_parse_tests pp_foundation_trace_tests pp_assets_image_format_tests pp_assets_ppi_header_tests pp_paint_blend_tests pp_paint_stroke_tests pp_document_tests pp_renderer_api_tests pp_paint_renderer_compositor_tests pp_ui_core_layout_value_tests pp_ui_core_layout_xml_tests}"
 start="$(date +%s)"
 
 cmake --preset "$preset"

src/paint/stroke.cpp

@@ -0,0 +1,162 @@
+#include "paint/stroke.h"
+
+#include <algorithm>
+#include <cmath>
+
+namespace pp::paint {
+
+namespace {
+
+[[nodiscard]] bool is_finite_point(const StrokePoint& point) noexcept
+{
+    return std::isfinite(point.x) && std::isfinite(point.y) && std::isfinite(point.pressure);
+}
+
+[[nodiscard]] float clamp_pressure(float pressure) noexcept
+{
+    return std::clamp(pressure, 0.0F, 1.0F);
+}
+
+[[nodiscard]] float distance_between(const StrokePoint& a, const StrokePoint& b) noexcept
+{
+    const auto dx = b.x - a.x;
+    const auto dy = b.y - a.y;
+    return std::sqrt(dx * dx + dy * dy);
+}
+
+[[nodiscard]] StrokeSample interpolate_sample(
+    const StrokePoint& a,
+    const StrokePoint& b,
+    float t,
+    float distance) noexcept
+{
+    return StrokeSample {
+        .x = a.x + ((b.x - a.x) * t),
+        .y = a.y + ((b.y - a.y) * t),
+        .pressure = clamp_pressure(a.pressure + ((b.pressure - a.pressure) * t)),
+        .distance = distance,
+    };
+}
+
+[[nodiscard]] pp::foundation::Status validate_input(
+    std::span<const StrokePoint> points,
+    StrokeSamplingConfig config) noexcept
+{
+    if (points.size() < 2U) {
+        return pp::foundation::Status::invalid_argument("stroke sampling requires at least two points");
+    }
+
+    if (points.size() > max_stroke_points) {
+        return pp::foundation::Status::out_of_range("stroke point count exceeds the configured limit");
+    }
+
+    if (!std::isfinite(config.spacing) || config.spacing <= 0.0F) {
+        return pp::foundation::Status::invalid_argument("stroke spacing must be finite and greater than zero");
+    }
+
+    if (config.max_samples == 0U || config.max_samples > max_stroke_samples) {
+        return pp::foundation::Status::out_of_range("stroke sample count limit is outside the configured range");
+    }
+
+    for (const auto& point : points) {
+        if (!is_finite_point(point)) {
+            return pp::foundation::Status::invalid_argument("stroke points must contain finite coordinates and pressure");
+        }
+    }
+
+    return pp::foundation::Status::success();
+}
+
+[[nodiscard]] pp::foundation::Status append_sample(
+    std::vector<StrokeSample>& samples,
+    StrokeSample sample,
+    std::size_t max_samples)
+{
+    if (samples.size() >= max_samples) {
+        return pp::foundation::Status::out_of_range("stroke sampling exceeded the configured sample limit");
+    }
+
+    samples.push_back(sample);
+    return pp::foundation::Status::success();
+}
+
+}
+
+pp::foundation::Result<std::vector<StrokeSample>> sample_stroke(
+    std::span<const StrokePoint> points,
+    StrokeSamplingConfig config) noexcept
+{
+    const auto input_status = validate_input(points, config);
+    if (!input_status.ok()) {
+        return pp::foundation::Result<std::vector<StrokeSample>>::failure(input_status);
+    }
+
+    std::vector<StrokeSample> samples;
+    samples.reserve(std::min<std::size_t>(points.size(), config.max_samples));
+
+    auto status = append_sample(
+        samples,
+        StrokeSample {
+            .x = points.front().x,
+            .y = points.front().y,
+            .pressure = clamp_pressure(points.front().pressure),
+            .distance = 0.0F,
+        },
+        config.max_samples);
+    if (!status.ok()) {
+        return pp::foundation::Result<std::vector<StrokeSample>>::failure(status);
+    }
+
+    float segment_start_distance = 0.0F;
+    float next_sample_distance = config.spacing;
+    float total_distance = 0.0F;
+
+    for (std::size_t i = 1; i < points.size(); ++i) {
+        const auto& a = points[i - 1U];
+        const auto& b = points[i];
+        const auto segment_length = distance_between(a, b);
+        if (segment_length <= 0.0F) {
+            continue;
+        }
+
+        const auto segment_end_distance = segment_start_distance + segment_length;
+        while (next_sample_distance <= segment_end_distance) {
+            const auto t = (next_sample_distance - segment_start_distance) / segment_length;
+            status = append_sample(
+                samples,
+                interpolate_sample(a, b, t, next_sample_distance),
+                config.max_samples);
+            if (!status.ok()) {
+                return pp::foundation::Result<std::vector<StrokeSample>>::failure(status);
+            }
+            next_sample_distance += config.spacing;
+        }
+
+        segment_start_distance = segment_end_distance;
+        total_distance = segment_end_distance;
+    }
+
+    if (total_distance <= 0.0F) {
+        return pp::foundation::Result<std::vector<StrokeSample>>::failure(
+            pp::foundation::Status::invalid_argument("stroke path must have nonzero length"));
+    }
+
+    if (config.include_endpoint && samples.back().distance < total_distance) {
+        status = append_sample(
+            samples,
+            StrokeSample {
+                .x = points.back().x,
+                .y = points.back().y,
+                .pressure = clamp_pressure(points.back().pressure),
+                .distance = total_distance,
+            },
+            config.max_samples);
+        if (!status.ok()) {
+            return pp::foundation::Result<std::vector<StrokeSample>>::failure(status);
+        }
+    }
+
+    return pp::foundation::Result<std::vector<StrokeSample>>::success(samples);
+}
+
+}

src/paint/stroke.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include "foundation/result.h"
+
+#include <cstddef>
+#include <cstdint>
+#include <span>
+#include <vector>
+
+namespace pp::paint {
+
+constexpr std::size_t max_stroke_points = 1000000;
+constexpr std::size_t max_stroke_samples = 1000000;
+
+struct StrokePoint {
+    float x = 0.0F;
+    float y = 0.0F;
+    float pressure = 1.0F;
+    std::uint32_t time_ms = 0;
+};
+
+struct StrokeSample {
+    float x = 0.0F;
+    float y = 0.0F;
+    float pressure = 1.0F;
+    float distance = 0.0F;
+};
+
+struct StrokeSamplingConfig {
+    float spacing = 1.0F;
+    bool include_endpoint = true;
+    std::size_t max_samples = max_stroke_samples;
+};
+
+[[nodiscard]] pp::foundation::Result<std::vector<StrokeSample>> sample_stroke(
+    std::span<const StrokePoint> points,
+    StrokeSamplingConfig config) noexcept;
+
+}

tests/CMakeLists.txt

@@ -66,6 +66,16 @@ add_test(NAME pp_paint_blend_tests COMMAND pp_paint_blend_tests)
 set_tests_properties(pp_paint_blend_tests PROPERTIES
     LABELS "paint;desktop-fast")
 
+add_executable(pp_paint_stroke_tests
+    paint/stroke_tests.cpp)
+target_link_libraries(pp_paint_stroke_tests PRIVATE
+    pp_paint
+    pp_test_harness)
+
+add_test(NAME pp_paint_stroke_tests COMMAND pp_paint_stroke_tests)
+set_tests_properties(pp_paint_stroke_tests PROPERTIES
+    LABELS "paint;desktop-fast")
+
 add_executable(pp_document_tests
     document/document_tests.cpp)
 target_link_libraries(pp_document_tests PRIVATE

tests/paint/stroke_tests.cpp

@@ -0,0 +1,128 @@
+#include "paint/stroke.h"
+#include "test_harness.h"
+
+#include <array>
+#include <cmath>
+
+using pp::foundation::StatusCode;
+using pp::paint::StrokePoint;
+using pp::paint::StrokeSamplingConfig;
+using pp::paint::max_stroke_samples;
+using pp::paint::sample_stroke;
+
+namespace {
+
+bool near(float a, float b)
+{
+    return std::fabs(a - b) < 0.0001F;
+}
+
+void samples_straight_line_at_fixed_spacing(pp::tests::Harness& h)
+{
+    const std::array points {
+        StrokePoint { .x = 0.0F, .y = 0.0F, .pressure = 0.25F },
+        StrokePoint { .x = 10.0F, .y = 0.0F, .pressure = 0.75F },
+    };
+
+    const auto result = sample_stroke(points, StrokeSamplingConfig { .spacing = 2.5F });
+    PP_EXPECT(h, result.ok());
+    PP_EXPECT(h, result.value().size() == 5U);
+    PP_EXPECT(h, near(result.value()[0].x, 0.0F));
+    PP_EXPECT(h, near(result.value()[1].x, 2.5F));
+    PP_EXPECT(h, near(result.value()[2].x, 5.0F));
+    PP_EXPECT(h, near(result.value()[3].x, 7.5F));
+    PP_EXPECT(h, near(result.value()[4].x, 10.0F));
+    PP_EXPECT(h, near(result.value()[2].pressure, 0.5F));
+    PP_EXPECT(h, near(result.value()[4].distance, 10.0F));
+}
+
+void carries_spacing_across_segments(pp::tests::Harness& h)
+{
+    const std::array points {
+        StrokePoint { .x = 0.0F, .y = 0.0F, .pressure = 1.0F },
+        StrokePoint { .x = 3.0F, .y = 0.0F, .pressure = 1.0F },
+        StrokePoint { .x = 3.0F, .y = 4.0F, .pressure = 0.0F },
+    };
+
+    const auto result = sample_stroke(points, StrokeSamplingConfig { .spacing = 2.0F });
+    PP_EXPECT(h, result.ok());
+    PP_EXPECT(h, result.value().size() == 5U);
+    PP_EXPECT(h, near(result.value()[1].x, 2.0F));
+    PP_EXPECT(h, near(result.value()[1].y, 0.0F));
+    PP_EXPECT(h, near(result.value()[2].x, 3.0F));
+    PP_EXPECT(h, near(result.value()[2].y, 1.0F));
+    PP_EXPECT(h, near(result.value()[3].x, 3.0F));
+    PP_EXPECT(h, near(result.value()[3].y, 3.0F));
+    PP_EXPECT(h, near(result.value()[4].distance, 7.0F));
+}
+
+void can_skip_endpoint_and_clamps_pressure(pp::tests::Harness& h)
+{
+    const std::array points {
+        StrokePoint { .x = 0.0F, .y = 0.0F, .pressure = -1.0F },
+        StrokePoint { .x = 5.0F, .y = 0.0F, .pressure = 2.0F },
+    };
+
+    const auto result = sample_stroke(
+        points,
+        StrokeSamplingConfig {
+            .spacing = 2.0F,
+            .include_endpoint = false,
+        });
+    PP_EXPECT(h, result.ok());
+    PP_EXPECT(h, result.value().size() == 3U);
+    PP_EXPECT(h, near(result.value()[0].pressure, 0.0F));
+    PP_EXPECT(h, near(result.value()[2].pressure, 1.0F));
+    PP_EXPECT(h, near(result.value()[2].distance, 4.0F));
+}
+
+void rejects_invalid_sampling_inputs(pp::tests::Harness& h)
+{
+    const std::array one_point {
+        StrokePoint { .x = 0.0F, .y = 0.0F },
+    };
+    const std::array zero_length {
+        StrokePoint { .x = 1.0F, .y = 1.0F },
+        StrokePoint { .x = 1.0F, .y = 1.0F },
+    };
+    const std::array non_finite {
+        StrokePoint { .x = 0.0F, .y = 0.0F },
+        StrokePoint { .x = std::nanf(""), .y = 1.0F },
+    };
+    const std::array valid {
+        StrokePoint { .x = 0.0F, .y = 0.0F },
+        StrokePoint { .x = 10.0F, .y = 0.0F },
+    };
+
+    const auto missing_points = sample_stroke(one_point, StrokeSamplingConfig {});
+    const auto bad_spacing = sample_stroke(valid, StrokeSamplingConfig { .spacing = 0.0F });
+    const auto bad_limit = sample_stroke(valid, StrokeSamplingConfig { .max_samples = max_stroke_samples + 1U });
+    const auto no_distance = sample_stroke(zero_length, StrokeSamplingConfig {});
+    const auto bad_point = sample_stroke(non_finite, StrokeSamplingConfig {});
+    const auto too_many = sample_stroke(valid, StrokeSamplingConfig { .spacing = 1.0F, .max_samples = 2U });
+
+    PP_EXPECT(h, !missing_points.ok());
+    PP_EXPECT(h, missing_points.status().code == StatusCode::invalid_argument);
+    PP_EXPECT(h, !bad_spacing.ok());
+    PP_EXPECT(h, bad_spacing.status().code == StatusCode::invalid_argument);
+    PP_EXPECT(h, !bad_limit.ok());
+    PP_EXPECT(h, bad_limit.status().code == StatusCode::out_of_range);
+    PP_EXPECT(h, !no_distance.ok());
+    PP_EXPECT(h, no_distance.status().code == StatusCode::invalid_argument);
+    PP_EXPECT(h, !bad_point.ok());
+    PP_EXPECT(h, bad_point.status().code == StatusCode::invalid_argument);
+    PP_EXPECT(h, !too_many.ok());
+    PP_EXPECT(h, too_many.status().code == StatusCode::out_of_range);
+}
+
+}
+
+int main()
+{
+    pp::tests::Harness harness;
+    harness.run("samples_straight_line_at_fixed_spacing", samples_straight_line_at_fixed_spacing);
+    harness.run("carries_spacing_across_segments", carries_spacing_across_segments);
+    harness.run("can_skip_endpoint_and_clamps_pressure", can_skip_endpoint_and_clamps_pressure);
+    harness.run("rejects_invalid_sampling_inputs", rejects_invalid_sampling_inputs);
+    return harness.finish();
+}