From fe96c4d1e323ab8e93d6b0a6c8948626ab6a387c Mon Sep 17 00:00:00 2001
From: Alexander Kojevnikov <alexander@kojevnikov.com>
Date: Thu, 6 May 2010 19:55:21 +1000
Subject: [PATCH] Use the visible spectrum

---
 src/spek-spectrogram.vala | 57 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 4 deletions(-)

diff --git a/src/spek-spectrogram.vala b/src/spek-spectrogram.vala
index 045e735..a89d3f4 100644
--- a/src/spek-spectrogram.vala
+++ b/src/spek-spectrogram.vala
@@ -6,6 +6,8 @@ namespace Spek {
 
 		private Source source;
 
+		private struct Color { uchar r; uchar g; uchar b; }
+
 		public Spectrogram () {
 		}
 
@@ -22,12 +24,59 @@ namespace Spek {
 			for (int y = 0; y < values.length; y++) {
 				var i = (values.length - y - 1) * rowstride + x * 3;
 				var level = float.min (1f, Math.log10f (101f + values[y]) / 2f);
-				var value = (uchar) (level * 255f);
-				pixels[i] = value;
-				pixels[i + 1] = value;
-				pixels[i + 2] = value;
+				var color = get_color (level);
+				if (sample < 20) {
+					// TODO: allocate additional space for this.
+					color = get_color (((float) y) / values.length);
+				}
+				pixels[i] = color.r;
+				pixels[i + 1] = color.g;
+				pixels[i + 2] = color.b;
 			}
 			queue_draw_area (allocation.x + sample, allocation.y, 1, allocation.height);
 		}
+
+		// Modified version of Dan Bruton's algorithm:
+		// http://www.physics.sfasu.edu/astro/color/spectra.html
+		private Color get_color (float level) {
+			float r = 0.0f, g = 0.0f, b = 0.0f;
+			if (level >= 0f && level < 0.15f) {
+				r = (0.15f - level) / (0.15f + 0.075f);
+				g = 0.0f;
+				b = 1.0f;
+			} else if (level >= 0.15f && level < 0.275f) {
+				r = 0.0f;
+				g = (level - 0.15f) / (0.275f - 0.15f);
+				b = 1.0f;
+			} else if (level >= 0.275f && level < 0.325f) {
+				r = 0.0f;
+				g = 1.0f;
+				b = (0.325f - level) / (0.325f - 0.275f);
+			} else if (level >= 0.325f && level < 0.5f) {
+				r = (level - 0.325f) / (0.5f - 0.325f);
+				g = 1.0f;
+				b = 0.0f;
+			} else if (level >= 0.5f && level < 0.6625f) {
+				r = 1.0f;
+				g = (0.6625f - level) / (0.6625f - 0.5f);
+				b = 0.0f;
+			} else if (level >= 0.6625 && level <= 1.0f) {
+				r = 1.0f;
+				g = 0.0f;
+				b = 0.0f;
+			}
+
+			// Intensity correction.
+			float cf = 0.0f;
+			if (level >= 0 && level < 0.1f) {
+				cf = 0.3f + 0.7f * (level + 0.075f) / (0.1f + 0.075f);
+			} else if (level >= 0.1f && level <= 0.8f) {
+				cf = 1.0f;
+			} else if (level > 0.8f && level <= 1.0f) {
+				cf = 0.3f + 0.7f * (1.0f - level) / (1.0f - 0.8f);
+			}
+			cf *= 255f;
+			return { (uchar) (r * cf + 0.5f), (uchar) (g * cf + 0.5f), (uchar) (b * cf + 0.5f) };
+		}
 	}
 }
\ No newline at end of file