implement numerically unstable mass spring system

src/renderer.cpp

@@ -0,0 +1,57 @@
+#include "renderer.hpp"
+
+#include "config.hpp"
+#include "mass_springs.hpp"
+
+auto Renderer::Rotate(const Vector3 &a, const float cos_angle,
+                      const float sin_angle) -> Vector3 {
+  return Vector3(a.x * cos_angle - a.z * sin_angle, a.y,
+                 a.x * sin_angle + a.z * cos_angle);
+};
+
+auto Renderer::Translate(const Vector3 &a, const float distance) -> Vector3 {
+  return Vector3(a.x, a.y, a.z + distance);
+};
+
+auto Renderer::Project(const Vector3 &a) -> Vector2 {
+  return Vector2(a.x / a.z, a.y / a.z);
+}
+
+auto Renderer::Map(const Vector2 &a) -> Vector2 {
+  return Vector2((1.0 + a.x) / 2.0 * width, (1.0 - a.y) * height / 2.0);
+}
+
+auto Renderer::Transform(Edge2Set &edges, const MassSpringSystem &mass_springs,
+                         const float angle, const float distance) -> void {
+  edges.clear();
+
+  const float cos_angle = cos(angle);
+  const float sin_angle = sin(angle);
+
+  for (const auto &spring : mass_springs.springs) {
+    Vector2 at = Map(Project(Translate(
+        Rotate(spring.massA.position, cos_angle, sin_angle), distance)));
+    Vector2 bt = Map(Project(Translate(
+        Rotate(spring.massB.position, cos_angle, sin_angle), distance)));
+
+    edges.emplace_back(at, bt);
+  }
+}
+
+auto Renderer::Draw(const Edge2Set &edges) -> void {
+  BeginTextureMode(render_target);
+  ClearBackground(RAYWHITE);
+  for (const auto &[a, b] : edges) {
+    DrawLine(a.x, a.y, b.x, b.y, EDGE_COLOR);
+    DrawCircle(a.x, a.y, VERTEX_SIZE, VERTEX_COLOR);
+    DrawCircle(b.x, b.y, VERTEX_SIZE, VERTEX_COLOR);
+  }
+  EndTextureMode();
+
+  BeginDrawing();
+  DrawTextureRec(render_target.texture,
+                 Rectangle(0, 0, (float)width, -(float)height), Vector2(0, 0),
+                 WHITE);
+  DrawFPS(10, 10);
+  EndDrawing();
+}