feat: project skeleton, core types and math with transform tests

include/plot/core/color.hpp

@@ -0,0 +1,22 @@
+#pragma once
+#include <plot/core/types.hpp>
+
+namespace plot {
+
+/// RGBA colour with components in [0,1].
+struct Color {
+  f32 r = 0.0f;
+  f32 g = 0.0f;
+  f32 b = 0.0f;
+  f32 a = 1.0f;
+
+  /// Build from a packed 0xRRGGBB literal, with an optional alpha override.
+  static constexpr Color hex(u32 rgb, f32 alpha = 1.0f) noexcept {
+    constexpr f32 kInv255 = 1.0f / 255.0f;
+    return Color{static_cast<f32>((rgb >> 16) & 0xFFu) * kInv255,
+                 static_cast<f32>((rgb >> 8) & 0xFFu) * kInv255,
+                 static_cast<f32>(rgb & 0xFFu) * kInv255, alpha};
+  }
+};
+
+}  // namespace plot

include/plot/core/rect.hpp

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+#pragma once
+#include <plot/core/types.hpp>
+
+namespace plot {
+
+/// Axis-aligned rectangle in pixels, origin at the top-left.
+struct Rect {
+  f32 x = 0.0f;
+  f32 y = 0.0f;
+  f32 w = 0.0f;
+  f32 h = 0.0f;
+
+  constexpr f32 right() const noexcept { return x + w; }
+  constexpr f32 bottom() const noexcept { return y + h; }
+
+  /// Half-open containment: the right/bottom edges are outside the rect.
+  constexpr bool contains(f32 px, f32 py) const noexcept {
+    return px >= x && px < right() && py >= y && py < bottom();
+  }
+};
+
+}  // namespace plot

include/plot/core/span.hpp

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+#pragma once
+#include <cstddef>
+#include <span>
+
+namespace plot {
+
+/// `std::span` re-exported so public headers and callers share one spelling.
+template <class T, std::size_t Extent = std::dynamic_extent>
+using Span = std::span<T, Extent>;
+
+}  // namespace plot

include/plot/core/status.hpp

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+#pragma once
+#include <plot/core/types.hpp>
+
+namespace plot {
+
+enum class ErrorCode {
+  Ok,
+  InvalidArgument,
+  OutOfMemory,
+  GLFailure,
+  Unsupported,
+  NotImplemented,
+};
+
+/// Never-null human-readable name of an error code.
+const char* to_string(ErrorCode code) noexcept;
+
+/// Result of a fallible operation. Falsy unless `code == ErrorCode::Ok`.
+struct Status {
+  ErrorCode code = ErrorCode::Ok;
+  const char* message = "";
+
+  constexpr explicit operator bool() const noexcept { return code == ErrorCode::Ok; }
+};
+
+}  // namespace plot

include/plot/core/types.hpp

@@ -0,0 +1,26 @@
+#pragma once
+#include <cstddef>
+#include <cstdint>
+
+namespace plot {
+
+using f32 = float;
+using f64 = double;
+using i32 = std::int32_t;
+using u32 = std::uint32_t;
+using u64 = std::uint64_t;
+using usize = std::size_t;
+
+/// Sentinel for "no index", e.g. an unmatched cursor id.
+constexpr u64 kInvalid = ~u64{0};
+
+/// Closed numeric interval on one axis.
+struct Range {
+  f64 min = 0.0;
+  f64 max = 1.0;
+
+  constexpr f64 span() const noexcept { return max - min; }
+  constexpr f64 clamp(f64 v) const noexcept { return v < min ? min : (v > max ? max : v); }
+};
+
+}  // namespace plot