From 4eb33aef1e9827cfb4ec7b12e9c843a01d8d9a91 Mon Sep 17 00:00:00 2001
From: Mike Walters <mike@flomp.net>
Date: Fri, 11 Sep 2015 00:16:55 +0100
Subject: [PATCH] Pre-calculate color map

Huge time savings in spectrogram generation.
Bit hacky at the moment with hard-coded size scattered everywhere.
Plan is to rejig this for custom color maps in the future, ref #4
---
 spectrogram.cpp | 7 ++++++-
 spectrogram.h   | 1 +
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/spectrogram.cpp b/spectrogram.cpp
index e6e1ec4..640937d 100644
--- a/spectrogram.cpp
+++ b/spectrogram.cpp
@@ -16,6 +16,11 @@ Spectrogram::Spectrogram()
 	zoomLevel = 0;
 	powerMax = 0.0f;
 	powerMin = -50.0f;
+
+	for (int i = 0; i < 256; i++) {
+		float p = (float)i / 256;
+		colormap[i] = QColor::fromHsvF(p * 0.83f, 1.0, 1.0 - p).rgba();
+	}
 }
 
 Spectrogram::~Spectrogram()
@@ -68,7 +73,7 @@ void Spectrogram::paintEvent(QPaintEvent *event)
 				float normPower = (line[x] - powerMax) * -1.0f / powerRange;
 				normPower = clamp(normPower, 0.0f, 1.0f);
 
-				image.setPixel(x, y, QColor::fromHsvF(normPower * 0.83f, 1.0, 1.0 - normPower).rgba());
+				image.setPixel(x, y, colormap[(uint8_t)(normPower * (256 - 1))]);
 			}
 		}
 
diff --git a/spectrogram.h b/spectrogram.h
index d9cc36e..bad1d79 100644
--- a/spectrogram.h
+++ b/spectrogram.h
@@ -37,6 +37,7 @@ private:
 	FFT *fft = nullptr;
 	std::unique_ptr<float[]> window;
 	fftwf_complex *lineBuffer = nullptr;
+	uint colormap[256];
 
 	int sampleRate;
 	int fftSize;