From 403ea4bb9fdd18f09d4ba38086e7bd2374220f62 Mon Sep 17 00:00:00 2001
From: Keuin <keuinx@gmail.com>
Date: Tue, 12 Apr 2022 10:17:14 +0800
Subject: Add basic object hit rendering. Add NOPRINT environ switch. Add demo
 sphere rendering.

---
 main_simple_scanner.cpp | 84 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 77 insertions(+), 7 deletions(-)

diff --git a/main_simple_scanner.cpp b/main_simple_scanner.cpp
index 103cfab..bc4e279 100644
--- a/main_simple_scanner.cpp
+++ b/main_simple_scanner.cpp
@@ -4,19 +4,76 @@
 
 #include <cstdint>
 #include <iostream>
+#include <vector>
+#include <memory>
+#include <cstdlib>
 
 #include "vec.h"
 #include "ray.h"
 #include "bitmap.h"
 #include "timer.h"
 
+#define DEMO_BALL
+
+class object {
+public:
+    // Will the given ray hit.
+    virtual bool hit(const ray3d &r) const = 0;
+
+    // object color, currently not parameterized
+    virtual pixel8b color() const = 0;
+
+    // subclasses must have virtual destructors
+    virtual ~object() = default;
+};
+
+class sphere : public object {
+    vec3d center;
+    double radius;
+
+public:
+    sphere() = delete;
+
+    sphere(const vec3d &center, double radius) : center(center), radius(radius) {}
+
+    ~sphere() override = default;
+
+    bool hit(const ray3d &r) const override {
+        // Ray: {Source, Direction, time}
+        // Sphere: {Center, radius}
+        // sphere hit formula: |Source + Direction * time - Center| = radius
+        // |(Sx + Dx * t - Cx, Sy + Dy * t - Cy, Sz + Dz * t - Cz)| = radius
+
+        // A = D dot D
+        const double a = dot(r.direction(), r.direction());
+        // B = 2(S - C) dot D
+        const double b = 2 * dot(r.source() - center, r.direction());
+        const auto rel_src = r.source() - center; // relative position of ray source
+        // C = (S - C) dot (S - C) - radius^2
+        const double c = dot(rel_src, rel_src) - radius * radius;
+        return b * b - 4 * a * c >= 0;
+    }
+
+    pixel8b color() const override {
+        return pixel8b::from_normalized(1.0, 0.0, 0.0);
+    }
+};
 
 class viewport {
     double half_width, half_height; // viewport size
     vec3d center; // coordinate of the viewport center point
+    std::vector<std::unique_ptr<object>> objects;
 
     // Given a ray from the camera, generate a color the camera seen on the viewport.
-    static pixel8b color(const ray3d &r) {
+    pixel8b color(const ray3d &r) {
+        // Detect hits
+        for (const auto &obj: objects) {
+            if (obj->hit(r)) {
+                return obj->color();
+            }
+        }
+
+        // Does not hit anything. Get background color (infinity)
         const auto u = (r.direction().y + 1.0) * 0.5;
         return mix(
                 pixel8b::from_normalized(1.0, 1.0, 1.0),
@@ -32,6 +89,11 @@ public:
     viewport(double width, double height, vec3d viewport_center) :
             half_width(width / 2.0), half_height(height / 2.0), center(viewport_center) {}
 
+    // Add an object to the world.
+    void add_object(std::unique_ptr<object> &&obj) {
+        objects.push_back(std::move(obj));
+    }
+
     // Generate the image seen on given viewpoint.
     bitmap8b render(vec3d viewpoint, uint16_t image_width, uint16_t image_height) {
         bitmap8b image{image_width, image_height};
@@ -55,22 +117,30 @@ public:
     }
 };
 
-void generate_image(uint16_t image_width, uint16_t image_height, double viewport_width, double focal_length) {
+void generate_image(uint16_t image_width, uint16_t image_height, double viewport_width, double focal_length,
+                    double sphere_z, double sphere_r) {
     double r = 1.0 * image_width / image_height;
     viewport vp{viewport_width, viewport_width / r, vec3d{0, 0, -focal_length}};
+    vp.add_object(std::unique_ptr<object>{new sphere{vec3d{0, 0, sphere_z}, sphere_r}});
     timer tm;
     tm.start_measure();
     const auto image = vp.render(vec3d::zero(), image_width, image_height); // camera position as the coordinate origin
     tm.stop_measure();
-    image.write_plain_ppm(std::cout);
+    if (!std::getenv("NOPRINT")) {
+        image.write_plain_ppm(std::cout);
+    } else {
+        std::cerr << "NOPRINT is defined. PPM Image won't be printed." << std::endl;
+    }
 }
 
 int main(int argc, char **argv) {
-    if (argc != 5) {
-        printf("Usage: %s <image_width> <image_height> <viewport_width> <focal_length>\n", argv[0]);
+    if (argc != 7) {
+        printf("Usage: %s <image_width> <image_height> <viewport_width> <focal_length> <sphere_z> <sphere_r>\n",
+               argv[0]);
         return 0;
     }
-    std::string iw{argv[1]}, ih{argv[2]}, vw{argv[3]}, fl{argv[4]};
+    std::string iw{argv[1]}, ih{argv[2]}, vw{argv[3]}, fl{argv[4]}, sz{argv[5]}, sr{argv[6]};
     generate_image(std::stoul(iw), std::stoul(ih),
-                   std::stod(vw), std::stod(fl));
+                   std::stod(vw), std::stod(fl),
+                   std::stod(sz), std::stod(sr));
 }
\ No newline at end of file
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