feat: add Cornell Box scene with orbit camera

- gfx::pipeline gains bind_vec3/bind_float for passing arbitrary
  uniforms to shaders (used for light position/color)
- scene base gains on_mouse_drag virtual hook; cuber.cpp polls
  left-mouse delta each frame and forwards it to the active scene
- cornell_box scene: 5-wall room (red/green/white), two pre-rotated
  white boxes with proportions from the original paper, an unlit
  ceiling light panel, and a point-light Lambert shader
- left-click drag orbits the camera around the scene origin;
  pitch is clamped to ±80° to prevent gimbal flip
- key 3 / --scene cornell_box selects the scene

cbt/gfx.cpp

@@ -34,6 +34,8 @@ struct pipeline::impl {
 
     auto build(pipeline_desc const& desc) -> bool;
     auto bind_texture(char const* sampler_name, std::uint32_t texture_id, std::uint32_t unit) const -> void;
+    auto bind_vec3(char const* name, glm::vec3 const& v) const -> void;
+    auto bind_float(char const* name, float v) const -> void;
 };
 
 auto pipeline::impl::build(pipeline_desc const& desc) -> bool {
@@ -105,6 +107,26 @@ auto pipeline::impl::build(pipeline_desc const& desc) -> bool {
 }
 
 
+auto pipeline::impl::bind_vec3(char const* name, glm::vec3 const& v) const -> void {
+    if (!m_prog.valid()) return;
+    m_prog.use();
+    GLint const loc = glGetUniformLocation(m_prog.id(), name);
+    if (loc != -1) {
+        glUniform3fv(loc, 1, glm::value_ptr(v));
+    }
+    m_prog.unuse();
+}
+
+auto pipeline::impl::bind_float(char const* name, float v) const -> void {
+    if (!m_prog.valid()) return;
+    m_prog.use();
+    GLint const loc = glGetUniformLocation(m_prog.id(), name);
+    if (loc != -1) {
+        glUniform1f(loc, v);
+    }
+    m_prog.unuse();
+}
+
 auto pipeline::impl::bind_texture(char const* sampler_name, std::uint32_t texture_id, std::uint32_t unit) const -> void {
     if (!m_prog.valid()) {
         return;
@@ -187,6 +209,18 @@ auto pipeline::bind_texture(char const* sampler_name, std::uint32_t texture_id,
     }
 }
 
+auto pipeline::bind_vec3(char const* name, glm::vec3 const& v) const -> void {
+    if (m_impl) {
+        m_impl->bind_vec3(name, v);
+    }
+}
+
+auto pipeline::bind_float(char const* name, float v) const -> void {
+    if (m_impl) {
+        m_impl->bind_float(name, v);
+    }
+}
+
 struct render_target::impl {
     GLuint m_fbo = 0;
     opengl::texture m_color{opengl::texture_target::_2d};

cbt/gfx.hpp

@@ -50,6 +50,8 @@ public:
     auto valid() const -> bool;
     auto draw(glm::mat4 const& model, glm::mat4 const& view, glm::mat4 const& proj) const -> void;
     auto bind_texture(char const* sampler_name, std::uint32_t texture_id, std::uint32_t unit = 0) const -> void;
+    auto bind_vec3(char const* name, glm::vec3 const& v) const -> void;
+    auto bind_float(char const* name, float v) const -> void;
 
 private:
     struct impl;

cbt/scene.cpp

@@ -10,4 +10,6 @@ auto scene::update(float) -> void {}
 
 auto scene::render(int, int) -> void {}
 
+auto scene::on_mouse_drag(double, double) -> void {}
+
 }

cbt/scene.hpp

@@ -11,6 +11,7 @@ public:
     virtual auto init() -> bool;
     virtual auto update(float delta_time) -> void;
     virtual auto render(int width, int height) -> void;
+    virtual auto on_mouse_drag(double dx, double dy) -> void;
 };
 
 }