Use std::clog instead of std::cerr to log progress

Fixes #935

Author: hollasch

CHANGELOG.md

@@ -20,7 +20,7 @@ Change Log -- Ray Tracing in One Weekend
   - Fix: CSS fix for cases where code listing overflow; change to fit content (#826)
   - Change: `hittable` member variable `ptr` renamed to `object`
   - Change: general rename of `mat_ptr` to `mat` (material)
-  - Change: hittable::bounding_box() signature has changed to always return a value (#859)
+  - Change: `hittable::bounding_box()` signature has changed to always return a value (#859)
   - Fix: Enabled compiler warnings for MSVC, Clang, GNU. Cleaned up warnings as fit (#865)
   - Change: replaced random vector in `isotropic` with `random_unit_vector`
   - Delete: `box`, `xy_rect`, `yz_rect`, `xz_rect` classes. Now replaced with new `quad` primitive
@@ -29,6 +29,7 @@ Change Log -- Ray Tracing in One Weekend
   - Added: New 2D `quad` primitive of arbitrary orientation (#756)
   - Added: New `box()` utility function returns `hittable_list` of new `quad` primitives (#780)
   - Fix: Add `\mathit` to italic math variables to fix slight kerning issues in equations (#839)
+  - Change: Use std::clog instead of std::cerr to log scanline progress (#935)
 
 ### In One Weekend
   - Added: More commentary about the choice between `double` and `float` (#752)

src/InOneWeekend/scene.h

@@ -27,7 +27,7 @@ class scene {
         std::cout << "P3\n" << image_width << ' ' << image_height << "\n255\n";
 
         for (int j = image_height-1; j >= 0; --j) {
-            std::cerr << "\rScanlines remaining: " << j << ' ' << std::flush;
+            std::clog << "\rScanlines remaining: " << j << ' ' << std::flush;
             for (int i = 0; i < image_width; ++i) {
                 color pixel_color(0,0,0);
                 for (int s = 0; s < samples_per_pixel; ++s) {
@@ -40,7 +40,7 @@ class scene {
             }
         }
 
-        std::cerr << "\nDone.\n";
+        std::clog << "\nDone.\n";
     }
 
   public: