From fefb5de652f3f07eda7bfb79ebb0134b64e5bd19 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Fri, 20 May 2016 23:53:22 +0200
Subject: Implement unit circle example

`unit_circle.sh` generates a animated GIF of the circle states between
p=1 and p=3.
---
 CMakeLists.txt | 12 ++++++++++++
 example.cc     |  2 +-
 src/color.h    |  2 ++
 unit_circle.cc | 39 +++++++++++++++++++++++++++++++++++++++
 unit_circle.sh | 17 +++++++++++++++++
 5 files changed, 71 insertions(+), 1 deletion(-)
 create mode 100644 unit_circle.cc
 create mode 100644 unit_circle.sh

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ccbfde7..6aeef3a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -17,8 +17,20 @@ add_executable(
 		src/ppm_pixel_stream.cc
 )
 
+add_executable(
+	unit_circle
+		unit_circle.cc
+		src/imgen.cc
+		src/ppm_pixel_stream.cc
+)
+
 target_link_libraries(
 	example
 		m
 		pthread
 )
+
+target_link_libraries(
+	unit_circle
+		m
+)
diff --git a/example.cc b/example.cc
index 294c86a..8e4eee8 100644
--- a/example.cc
+++ b/example.cc
@@ -64,7 +64,7 @@ void generate_minkowski_voronoi(
 				];
 
 				if ( *minimal_distance <= 5 ) {
-					return imgen::color(0, 0, 0);
+					return imgen::black();
 				} else {
 					return std::get<2>(nearest);
 				}
diff --git a/src/color.h b/src/color.h
index 514c739..dcad5cf 100644
--- a/src/color.h
+++ b/src/color.h
@@ -7,6 +7,8 @@ namespace imgen {
 
 using color = std::tuple<std::uint8_t, std::uint8_t, std::uint8_t>;
 
+constexpr color black()   { return color{  0,   0,   0}; }
+constexpr color white()   { return color{255, 255, 255}; }
 constexpr color red()     { return color{255,   0,   0}; }
 constexpr color lime()    { return color{  0, 255,   0}; }
 constexpr color blue()    { return color{  0,   0, 255}; }
diff --git a/unit_circle.cc b/unit_circle.cc
new file mode 100644
index 0000000..283fb53
--- /dev/null
+++ b/unit_circle.cc
@@ -0,0 +1,39 @@
+#include <imgen.h>
+
+#include <cmath>
+#include <vector>
+#include <algorithm>
+
+int p_norm(double p, int x, int y) {
+	return static_cast<int>(std::nearbyint(
+		std::pow(
+			std::pow(std::abs(x), p) + std::pow(std::abs(y), p),
+			1.0 / p
+		)
+	));
+}
+
+void generate_p_unit_circle(
+	const double lower,
+	const double upper,
+	const double epsilon
+) {
+	for ( double p = lower; p < upper + epsilon; p = p + epsilon ) {
+		imgen::write_ppm(
+			"unit_circle_" + std::to_string(p) + ".ppm",
+			128,
+			128,
+			[p](std::ptrdiff_t x, std::ptrdiff_t y) -> imgen::color {
+				if ( p_norm(p, x, y) <= 32 ) {
+					return imgen::black();
+				} else {
+					return imgen::white();
+				}
+			}
+		);
+	}
+}
+
+int main(int, char*[]) {
+	generate_p_unit_circle(1.0, 3.0, 0.05);
+}
diff --git a/unit_circle.sh b/unit_circle.sh
new file mode 100644
index 0000000..40c834f
--- /dev/null
+++ b/unit_circle.sh
@@ -0,0 +1,17 @@
+#! /usr/bin/fish
+
+mkdir unit ^/dev/null
+cd unit
+rm *.ppm *.gif ^/dev/null
+
+../unit_circle
+
+for f in unit_circle_*
+	convert $f -annotate +75+120 (echo "p =" (echo $f | grep -o "[0-9].[0-9]\{2\}" | head -n 1)) $f
+end
+
+convert -delay 8 -loop 0 *.ppm circle.gif
+convert -reverse circle.gif circle_reversed.gif
+convert circle.gif circle_reversed.gif circle_cycle.gif
+
+cd ..
-- 
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