From 6b75f48005c9e4ded84ef43a25ac1f1ae5c88971 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Wed, 4 Jul 2018 20:35:37 +0200
Subject: [PATCH] Factor out the RGB conversion code into a header file.

---
 flow.cpp   | 44 ++++++++++----------------------------------
 flow2rgb.h | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 34 deletions(-)
 create mode 100644 flow2rgb.h

diff --git a/flow.cpp b/flow.cpp
index 8e823e7..47cebba 100644
--- a/flow.cpp
+++ b/flow.cpp
@@ -16,6 +16,8 @@
 #include <assert.h>
 #include <stdio.h>
 
+#include "flow2rgb.h"
+
 #include <algorithm>
 #include <memory>
 
@@ -520,40 +522,14 @@ int main(void)
 			float dv = dense_flow[(yy * level_width + x) * 3 + 1];
 			float w = dense_flow[(yy * level_width + x) * 3 + 2];
 
-			du /= w;
-			dv /= w;
-
-			float angle = atan2(dv * level_width, du * level_height);
-			float magnitude = min(hypot(du * level_width, dv * level_height) / 20.0, 1.0);
-			
-			// HSV to RGB (from Wikipedia). Saturation is 1.
-			float c = magnitude;
-			float h = (angle + M_PI) * 6.0 / (2.0 * M_PI);
-			float X = c * (1.0 - fabs(fmod(h, 2.0) - 1.0));
-			float r = 0.0f, g = 0.0f, b = 0.0f;
-			if (h < 1.0f) {
-				r = c; g = X;
-			} else if (h < 2.0f) {
-				r = X; g = c;
-			} else if (h < 3.0f) {
-				g = c; b = X;
-			} else if (h < 4.0f) {
-				g = X; b = c;
-			} else if (h < 5.0f) {
-				r = X; b = c;
-			} else if (h < 6.0f) {
-				r = c; b = X;
-			} else {
-				// h is NaN, so black is fine.
-			}
-			float m = magnitude - c;
-			r += m; g += m; b += m;
-			r = max(min(r, 1.0f), 0.0f);
-			g = max(min(g, 1.0f), 0.0f);
-			b = max(min(b, 1.0f), 0.0f);
-			putc(lrintf(r * 255.0f), fp);
-			putc(lrintf(g * 255.0f), fp);
-			putc(lrintf(b * 255.0f), fp);
+			du = (du / w) * level_width;
+			dv = (dv / w) * level_height;
+
+			uint8_t r, g, b;
+			flow2rgb(du, dv, &r, &g, &b);
+			putc(r, fp);
+			putc(g, fp);
+			putc(b, fp);
 		}
 	}
 	fclose(fp);
diff --git a/flow2rgb.h b/flow2rgb.h
new file mode 100644
index 0000000..ca17530
--- /dev/null
+++ b/flow2rgb.h
@@ -0,0 +1,45 @@
+#ifndef _FLOW2RGB_H
+#define _FLOW2RGB_H 1
+
+#include <math.h>
+#include <stdint.h>
+
+#include <algorithm>
+
+// du and dv are in pixels.
+inline void flow2rgb(float du, float dv, uint8_t *rr, uint8_t *gg, uint8_t *bb)
+{
+	float angle = atan2(dv, du);
+	float magnitude = std::min(hypot(du, dv) / 20.0, 1.0);
+	
+	// HSV to RGB (from Wikipedia). Saturation is 1.
+	float c = magnitude;
+	float h = (angle + M_PI) * 6.0 / (2.0 * M_PI);
+	float X = c * (1.0 - fabs(fmod(h, 2.0) - 1.0));
+	float r = 0.0f, g = 0.0f, b = 0.0f;
+	if (h < 1.0f) {
+		r = c; g = X;
+	} else if (h < 2.0f) {
+		r = X; g = c;
+	} else if (h < 3.0f) {
+		g = c; b = X;
+	} else if (h < 4.0f) {
+		g = X; b = c;
+	} else if (h < 5.0f) {
+		r = X; b = c;
+	} else if (h < 6.0f) {
+		r = c; b = X;
+	} else {
+		// h is NaN, so black is fine.
+	}
+	float m = magnitude - c;
+	r += m; g += m; b += m;
+	r = std::max(std::min(r, 1.0f), 0.0f);
+	g = std::max(std::min(g, 1.0f), 0.0f);
+	b = std::max(std::min(b, 1.0f), 0.0f);
+	*rr = lrintf(r * 255.0f);
+	*gg = lrintf(g * 255.0f);
+	*bb = lrintf(b * 255.0f);
+}
+
+#endif  // !defined(_FLOW2RGB_H)
-- 
2.39.2