From 01f5ff46d222ee137a87a69cae430421e50c21b5 Mon Sep 17 00:00:00 2001
From: Keuin <keuinx@gmail.com>
Date: Thu, 14 Apr 2022 13:43:28 +0800
Subject: Use flexible intermediate color depth when rendering. Note: further
 debugging is needed. The output image quality won't be improved when using
 16bit/32bit internal color depth.

---
 bitmap.h                | 17 +++++++++++++++--
 main_simple_scanner.cpp | 17 ++++++++++-------
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/bitmap.h b/bitmap.h
index b35bf81..a5b05e6 100644
--- a/bitmap.h
+++ b/bitmap.h
@@ -136,11 +136,25 @@ public:
             width(width), height(height), content{data} {}
 
     static bitmap<T> average(const std::vector<bitmap<T>> &images) {
+        using Acc = typename std::conditional<
+                (sizeof(T) <= 1),
+                uint_fast16_t,
+                typename std::conditional<
+                        (sizeof(T) <= 2),
+                        uint_fast32_t,
+                        typename std::conditional<
+                                (sizeof(T) <= 4),
+                                uint_fast64_t,
+                                uintmax_t
+                        >::type
+                >::type
+        >::type; // pick the smallest suitable type for accumulator
+        static_assert(sizeof(Acc) > sizeof(T), "accumulator may overflow");
         assert(!images.empty());
         bitmap<T> result{images[0].width, images[0].height};
         const auto m = images.size();
         const auto n = images[0].content.size();
-        uint_fast32_t acc_r, acc_g, acc_b;
+        Acc acc_r, acc_g, acc_b;
         for (size_t i = 0; i < n; ++i) {
             acc_r = 0;
             acc_g = 0;
@@ -197,7 +211,6 @@ public:
         bitmap<T> out{shape.first, shape.second};
         for (size_t i = 0; i < sz; ++i) {
             out[i] = pixel<T>::from(src[i]);
-            std::cerr << (int) out[i].r << ' ' << (int) out[i].g << ' ' << (int) out[i].b << std::endl;
         }
         return out;
     }
diff --git a/main_simple_scanner.cpp b/main_simple_scanner.cpp
index bd870d7..26518b1 100644
--- a/main_simple_scanner.cpp
+++ b/main_simple_scanner.cpp
@@ -17,6 +17,8 @@
 
 #define DEMO_BALL
 
+// T: intermediate color depth
+template<typename T>
 void generate_image(uint16_t image_width, uint16_t image_height, double viewport_width, double focal_length,
                     double sphere_z, double sphere_r, unsigned samples, const std::string &caption = "",
                     unsigned caption_scale = 1) {
@@ -26,13 +28,13 @@ void generate_image(uint16_t image_width, uint16_t image_height, double viewport
         std::cerr << "Antialiasing Samples: " << samples << std::endl;
     }
     double r = 1.0 * image_width / image_height;
-    viewport8b *vp;
+    viewport<T> *vp;
     if (samples == 1) {
-        vp = new basic_viewport8b{viewport_width, viewport_width / r, vec3d{0, 0, -focal_length}};
+        vp = new basic_viewport<T>{viewport_width, viewport_width / r, vec3d{0, 0, -focal_length}};
     } else {
-        vp = new aa_viewport8b{viewport_width, viewport_width / r, vec3d{0, 0, -focal_length}, samples};
+        vp = new aa_viewport<T>{viewport_width, viewport_width / r, vec3d{0, 0, -focal_length}, samples};
     }
-    hitlist8b world;
+    hitlist<T> world;
     world.add_object(std::make_shared<sphere>(
             vec3d{0, -100.5, -1},
             100)); // the earth
@@ -44,11 +46,12 @@ void generate_image(uint16_t image_width, uint16_t image_height, double viewport
     tm.stop_measure();
     if (!caption.empty()) {
         image.print(caption,
-                    pixel8b::from_normalized(1.0, 0.0, 0.0),
+                    pixel<T>::from_normalized(1.0, 0.0, 0.0),
                     10, 10, caption_scale, 0.8);
     }
+    const auto image8b = bitmap8b::from<T>(image);
     if (!std::getenv("NOPRINT")) {
-        image.write_plain_ppm(std::cout);
+        image8b.write_plain_ppm(std::cout);
     } else {
         std::cerr << "NOPRINT is defined. PPM Image won't be printed." << std::endl;
     }
@@ -71,7 +74,7 @@ int main(int argc, char **argv) {
         cap = std::string{argv[8]};
     }
     const auto image_width = std::stoul(iw);
-    generate_image(image_width, std::stoul(ih),
+    generate_image<uint16_t>(image_width, std::stoul(ih),
                    std::stod(vw), std::stod(fl),
                    std::stod(sz), std::stod(sr),
                    std::stoul(sp), cap,
-- 
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