From 8296be848319eecd43f94900d4d12414ec189166 Mon Sep 17 00:00:00 2001
From: Julian T <julian@jtle.dk>
Date: Wed, 3 Feb 2021 15:34:17 +0100
Subject: Add simple perspective camera

---
 src/camera/camera.rs | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/camera/mod.rs    |  4 ++-
 src/core/vector3.rs  | 29 ++++++++++++++++-
 src/lib.rs           |  4 ++-
 src/main.rs          | 13 ++++++++
 5 files changed, 137 insertions(+), 3 deletions(-)
 create mode 100644 src/camera/camera.rs

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;
diff --git a/src/core/vector3.rs b/src/core/vector3.rs
index 915765d..6f4d6ab 100644
--- a/src/core/vector3.rs
+++ b/src/core/vector3.rs
@@ -2,7 +2,8 @@
 //!
 //! Also add more 3d math things needed for shading and 3d calculations.
 use crate::{Float, Number};
-use std::ops::{Sub, Add, DivAssign};
+use std::ops::{Mul, Sub, Add, DivAssign};
+use std::fmt;
 
 #[derive(Clone, Copy)]
 pub struct Vector3<T: Number> {
@@ -49,6 +50,17 @@ impl<T: Number> Add for Vector3<T> {
     }
 }
 
+impl<T: Number> Mul<T> for Vector3<T> {
+    type Output = Self;
+    fn mul(self, op: T) -> Self::Output {
+        Self::Output::new_xyz(
+            self.x * op,
+            self.y * op,
+            self.z * op,
+            )
+    }
+}
+
 impl<T: Number> DivAssign<T> for Vector3<T> {
     fn div_assign(&mut self, op: T) {
         self.x /= op;
@@ -57,6 +69,12 @@ impl<T: Number> DivAssign<T> for Vector3<T> {
     }
 }
 
+impl<T: Number> fmt::Display for Vector3<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_fmt(format_args!("[{}, {}, {}]", self.x, self.y, self.z))
+    }
+}
+
 impl Vector3f {
     /// Calculates the length times itself
     ///
@@ -97,4 +115,13 @@ impl Vector3f {
         new.norm_in();
         new
     }
+
+    pub fn cross(&self, op: &Self) -> Self {
+        Self::new_xyz(
+            self.y * op.z - self.z * op.y,
+            self.z * op.x - self.x * op.z,
+            self.x * op.y - self.y * op.x,
+            )
+
+    }
 }
diff --git a/src/lib.rs b/src/lib.rs
index df9bc1d..c3025b3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,6 +4,7 @@ mod scene;
 
 use std::ops::{Add, Sub, Mul, DivAssign};
 use std::cmp;
+use std::fmt;
 
 /// Trait used to implement generics
 ///
@@ -14,7 +15,8 @@ pub trait Number:
     Sub<Output = Self> +
     Add<Output = Self> +
     Mul<Output = Self> +
-    DivAssign
+    DivAssign +
+    fmt::Display
 {}
 
 impl Number for i32 {}
diff --git a/src/main.rs b/src/main.rs
index 524f613..22998dd 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,17 @@
+use pathtrace::camera::Camera;
+use pathtrace::core::{Vector3f, Vector2f};
 
 
 fn main() {
+
+    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));
+
+    println!("r: {}, norm: {}", r.direction, r.direction.norm());
 }
-- 
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