LibGfx: Add Painter::draw_triangle_wave()

This patch adds support for drawing triangular waves.
For now those can only be horizontal, but as they are intended for
underlining text, it's an okay way to handle this.

2 files changed, 21 insertions, 0 deletions

diff --git a/Userland/Libraries/LibGfx/Painter.cpp b/Userland/Libraries/LibGfx/Painter.cpp
index d58b506e10..3576d32f5b 100644
--- a/Userland/Libraries/LibGfx/Painter.cpp
+++ b/Userland/Libraries/LibGfx/Painter.cpp
@@ -3,6 +3,7 @@
  * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
  * Copyright (c) 2021, Mustafa Quraish <mustafa@serenityos.org>
  * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2022, Tobias Christiansen <tobyase@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -1821,6 +1822,25 @@ void Painter::draw_line(IntPoint const& a_p1, IntPoint const& a_p2, Color color,
     }
 }
 
+void Painter::draw_triangle_wave(IntPoint const& a_p1, IntPoint const& a_p2, Color color, int amplitude, int thickness)
+{
+    // FIXME: Support more than horizontal waves
+    VERIFY(a_p1.y() == a_p2.y());
+
+    auto const p1 = thickness > 1 ? a_p1.translated(-(thickness / 2), -(thickness / 2)) : a_p1;
+    auto const p2 = thickness > 1 ? a_p2.translated(-(thickness / 2), -(thickness / 2)) : a_p2;
+
+    auto point1 = to_physical(p1);
+    auto point2 = to_physical(p2);
+
+    auto y = point1.y();
+
+    for (int x = 0; x <= point2.x() - point1.x(); ++x) {
+        auto y_offset = abs(x % (2 * amplitude) - amplitude) - amplitude;
+        draw_physical_pixel({ point1.x() + x, y + y_offset }, color, thickness);
+    }
+}
+
 static bool can_approximate_bezier_curve(FloatPoint const& p1, FloatPoint const& p2, FloatPoint const& control)
 {
     constexpr static int tolerance = 15;
diff --git a/Userland/Libraries/LibGfx/Painter.h b/Userland/Libraries/LibGfx/Painter.h
index 8b9e407846..e95be51324 100644
--- a/Userland/Libraries/LibGfx/Painter.h
+++ b/Userland/Libraries/LibGfx/Painter.h
@@ -59,6 +59,7 @@ public:
     void set_pixel(IntPoint const&, Color);
     void set_pixel(int x, int y, Color color) { set_pixel({ x, y }, color); }
     void draw_line(IntPoint const&, IntPoint const&, Color, int thickness = 1, LineStyle style = LineStyle::Solid, Color alternate_color = Color::Transparent);
+    void draw_triangle_wave(IntPoint const&, IntPoint const&, Color color, int amplitude, int thickness = 1);
     void draw_quadratic_bezier_curve(IntPoint const& control_point, IntPoint const&, IntPoint const&, Color, int thickness = 1, LineStyle style = LineStyle::Solid);
     void draw_cubic_bezier_curve(IntPoint const& control_point_0, IntPoint const& control_point_1, IntPoint const&, IntPoint const&, Color, int thickness = 1, LineStyle style = LineStyle::Solid);
     void draw_elliptical_arc(IntPoint const& p1, IntPoint const& p2, IntPoint const& center, FloatPoint const& radii, float x_axis_rotation, float theta_1, float theta_delta, Color, int thickness = 1, LineStyle style = LineStyle::Solid);