Add simple perspective camera

2 files changed, 93 insertions, 1 deletions

diff --git a/src/camera/camera.rs b/src/camera/camera.rs
new file mode 100644
index 0000000..69fd4e0
--- /dev/null
+++ b/src/camera/camera.rs
@@ -0,0 +1,90 @@
+//! Generates rays from screen coordinates
+//!
+//! Generates rays in world space from screen coordinates.
+//! Future versions should also simulate depth of field.
+//!
+//! # Examples
+//!
+//! ```
+//! use pathtrace::camera::Camera;
+//! use pathtrace::core::{Vector3f, Vector2f};
+//!
+//! let cam = Camera::new(
+//!     Vector3f::new(10.0), 
+//!     Vector3f::new(0.0), 
+//!     Vector3f::new_xyz(0.0, 1.0, 0.0), 
+//!     90.0, Vector2f::new(10.0),
+//!     );
+//!
+//! let (r, _) = cam.generate_ray(&Vector2f::new(5.0));
+//! let dir = r.direction;
+//!
+//! assert!(
+//!     dir.x == -0.44792563 &&
+//!     dir.y == -0.659974 &&
+//!     dir.z == -0.6031559
+//!     );
+//!
+//! ```
+use crate::Float;
+use crate::core::{Vector3f, Vector2f, Ray};
+
+/// A simple perspective camera
+pub struct Camera {
+    /// The camera origin in the screen
+    origin: Vector3f,
+    /// Vector from camera origin to the screen lower left corner
+    screen_origin: Vector3f,
+    /// Scaling vectors from screen_origin
+    qx: Vector3f,
+    qy: Vector3f,
+}
+
+impl Camera {
+    /// Create a new camera look at a target
+    ///
+    /// The field of view specifies how wide the image should be.
+    /// Currently must be between [0; 180[.
+    pub fn new(origin: Vector3f, target: Vector3f, up: Vector3f, fov: Float, screensize: Vector2f) -> Camera {
+        // Calculate translation vectors
+        let forward = (target - origin).norm();
+        let right = up.cross(&origin).norm();
+        let newup = forward.cross(&right).norm();
+
+        // Calculate screen size from fov
+        let aspect = screensize.y / screensize.x;
+        let width = 2.0 * (fov / 2.0).to_radians().tan();
+        let height = aspect * width;
+
+        // Calculate screen scaling vectors
+        let qx = right * (width / (screensize.x - 1.0));
+        let qy = newup * (height / (screensize.y - 1.0));
+
+        let screen_origin = forward - (right * (width/2.0)) - (newup * (height/2.0));
+
+        Camera {
+            origin,
+            screen_origin,
+            qx,
+            qy,
+        }
+    }
+
+    /// Generates a ray a screen space point
+    ///
+    /// The point coordinates should be between [0,0] (lower left corner) and [screensize.x,
+    /// screensize.y] (upper right corner)
+    ///
+    /// Will return a ray and a weight
+    ///
+    /// The direction of the returned way is normalized
+    pub fn generate_ray(&self, point: &Vector2f) -> (Ray, Float) {
+        let mut dir = self.screen_origin + (self.qx * point.x) + (self.qy * point.y);
+        dir.norm_in();
+
+        (
+            Ray { origin: self.origin, direction: dir },
+            1.0
+            )
+    }
+}
diff --git a/src/camera/mod.rs b/src/camera/mod.rs
index 4865a36..b7c982b 100644
--- a/src/camera/mod.rs
+++ b/src/camera/mod.rs
@@ -7,4 +7,6 @@
 
 pub mod film;
 //pub mod filter;
-//pub mod camera;
+pub mod camera;
+
+pub use camera::Camera;